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UBC Theses and Dissertations

Image isocon television system for the detection of astronomical spectra Buchholz, Vernon Lawrence 1972

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C I IMAGE ISOCON TELEVISION SYSTEM FOR THE DETECTION OF ASTRONOMICAL SPECTRA by VERNON LAWRENCE BUCHHOLZ B . S c , S t . Lojuis U n i v e r s i t y , 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department o f GEOPHYSICS AND ASTRONOMY We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA September, 1972 In present ing t h i s thes is in p a r t i a l f u l f i l m e n t o f the requirements for an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I fu r ther agree that permission for extensive copying o f th is t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h is representa t ives . It is understood that copying or p u b l i c a t i o n o f t h i s thes is f o r f i n a n c i a l gain s h a l l not be allowed without my wr i t ten permiss ion . Department of Geophysics and A s t r o n o m y The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date g p p t p m h P r ? R r 1972 i ABSTRACT A complete system f o r the d e t e c t i o n and r e c o r d i n g of a s t r o n o m i c a l s p e c t r a has been c o n s t r u c t e d using an image isocon (E.E.V. P850) t e l e v i s i o n tube as d e t e c t o r . The d e t e c t o r w i l l accomodate two s p e c t r a 80 m i l l i m e t e r s i n l e n g t h and has the s p e c t r a l response of an S-20 photocathode. Recording i s onto IBM-compatible magnetic tape v i a an o n - l i n e computer. The user i s a l s o provided with a r e a l time d i s p l a y of the s p e c t r a on an o s c i l l o s c o p e v i a the computer. A d e s c r i p t i o n of the video s i g n a l c i r c u i t s i s g i v e n . Schematic diagrams of the c o n t r o l u n i t c o n s t r u c t e d by the author and the modified camera are shown. A method of determining the modulation t r a n s f e r f u n c t i o n of the d e t e c t o r , based on the F o u r i e r a n a l y s i s of the s i g n a l output f o r a known s i g n a l i n p u t , i s d e s c r i b e d . The MTF as a f u n c t i o n of l i g h t l e v e l , exposure time, and t a r g e t temperature i s i n v e s t i g a t e d . It can be seen that the best MTF f o r a p a r t i c u l a r exposure time occurs at the lowest t a r g e t temperature. The MTF f a r exceeds that p r e d i c t e d as the maximum by d i r e c t a p p l i c a t i o n of the a n a l y s i s of Krittman (1962). I t i s i i assumed that the Krittman a n a l y s i s can not be a p p l i e d to the P850 image isocon with i t s l a r g e t a r g e t mesh-to-t a r g e t spacing and t h i n t a r g e t . i i i TABLE OF CONTENTS Page INTRODUCTION 1 THE ISOCON TUBE AND CAMERA 5 THE VIDEO SIGNAL CIRCUITS 9 THE MODULATION TRANSFER FUNCTION 13 CONCLUSION 50 BIBLIOGRAPHY 52 APPENDIX A (SYSTEM SCHEMATICS) 53 APPENDIX B (COMPUTER PROGRAMS) 60 LIST OF FIGURES Figure Page 1 System block diagram 2 2 Isocon tube schematic 6 3 Video signals 10 4 Video signal c i r c u i t 11 5 Typical detector MTF 14 6 Signal output versus separation of l i n e 17 scans 7 Krittman t h e o r e t i c a l maximum MTF 20 8 MTF test set-up 22 9 Test pattern 23 10 Test pattern output 26 11 MTF measurement process 28 12 MTF as a function of l i g h t l e v e l 31 13 MTF at -15 #C 33 14 MTF at 0*C 38 V LIST DF TABLES Tab le Page 1 MTF at - 1 5 ° C , Exposure time 17 s e c o n d s , 41 low l i g h t l e v e l 2 MTF at - 1 5 ° C , Exposure time 17 s e c o n d s , 42 medium l i g h t l e v e l 3 MTF at - 1 5 ° C , Exposure time 35 s e c o n d s , 43 medium l i g h t l e v e l 4 MTF at - 1 5 ° C , Exposure time 77 s e c o n d s , 44 medium l i g h t l e v e l 5 MTF at - 1 5 ° C , Exposure time 151 s e c o n d s , 45 medium l i g h t l e v e l 6 MTF at - 1 5 ° C , Exposure time 298 s e c o n d s , 46 medium l i g h t l e v e l 7 MTF at 0 ° C , Exposure time 17 s e c o n d s , 47 medium l i g h t l e v e l 8 MTF at 0 ° C , Exposure time 35 s e c o n d s , 48 medium l i g h t l e v e l 9 MTF at 0 * C , Exposure time 77 s e c o n d s , 49 medium l i g h t l e v e l v i ACKNOWLEDGEMENTS I would l i k e to acknowledge the he lp and e n c o u r -agement of the f a c u l t y and s t a f f of the Department o f Geophys ics and Astronomy. In p a r t i c u l a r I would l i k e to thank the f o l l o w i n g people and i n s t i t u t i o n s . D r s . J . R . Auman, T . J . U l r y c h , and G . A . H . Walker , my a d v i s o r s , o f f e r e d much he lp and i n s p i r a t i o n . M e s s r s . R. C o u t t s , B . A . G o l d b e r g , B. Isherwood, and R „ Knight gave t e c h n i c a l a d v i c e and he lp i n c o n s t r u c t i o n o f the equ ip tment . Ms. Jean E i l e k o f f e r e d much he lp wi th the computer programming. T h i s work was f i n a n c e d by a s c h o l a r s h i p from the U n i v e r s i t y o f B r i t i s h Columbia and a grant from the N a t i o n a l Research C o u n c i l o f Canada. 1 INTRODUCTION Recent advances i n t e l e v i s i o n techno logy have brought about new methods of d e t e c t i o n of a s t r o n o m i c a l s p e c t r a , to r e p l a c e the much u s e d , but o f t e n u n s a t i s f a c t o r y , p h o t o -g r a p h i c p l a t e or p h o t o m u l t i p l i e r image s c a n n e r . But to be a u s e f u l a l t e r n a t i v e , any t e l e v i s i o n d e t e c t o r must combine the i n t e g r a t i n g c a p a c i t y o f the pho tograph ic p l a t e and the p h o t o -e l e c t r i c p r e c i s i o n o f the p h o t o m u l t i p l i e r , wi th as h igh a s p a t i a l r e s o l u t i o n as p o s s i b l e . In view of these r e q u i r e m e n t s , a system f o r the d e t e c t i o n and r e c o r d i n g of a s t r o n o m i c a l s p e c t r a has been c o n s t r u c t e d at the I n s t i t u t e of Astronomy and Space S c i e n c e at the U n i v e r s i t y o f B r i t i s h C o l u m b i a . The system uses as a d e t e c t o r an E . E . V . PB50 image i s o c o n t e l e v i s i o n t u b e , c o o l e d by f o r c e d a i r to about 0 ° C , i n a g r e a t l y m o d i f i e d Marconi TF1709 camera. The data a c q u i s i t i o n and r e c o r d i n g system c o n s i s t s of a B iomat ion 12 b i t a n a l o g - t o - d i g i t a l c o n v e r t e r , I n t e r d a t a Model 4 computer w i th o s c i l l o s c o p e d i s p l a y , and a PEC magnet ic tape t r a n s p o r t . The whole system i s shown i n b lock diagram form i n F igure 1. Two s p e c t r a are imaged onto the face of the i s o c o n t u b e . A f t e r s u f f i c i e n t l i g h t has f a l l e n on the i s o c o n to p r o -duce a u s e f u l s i g n a l , an e l e c t r o n r e a d i n g beam scans the t a r -get of the tube with a t e l e v i s i o n - t y p e r a s t e r of up to 999 S Y S T E M B L O C K D I A G R A M I S O C O N C A M E R A M A S T F R C O N T R O L U N I T VIDEO SIGNAL ZF G A T E I  G A T E 2 I N T E G R A T O R I I N T E G R A T O R 2 M U L T I -P L E X E R -7 L O G I C C O N T R O L UN I T C O M P U T E R O S C I L L O -S C O P E M/ D l S P L A Y L I G H T S F I G U R E I 3 n o n - i n t e r l a c e d l i n e s . The l i n e scan i s normal to the s p e c t r a l d i s p e r s i o n . The tube thus produces a c u r r e n t v e r s u s time o u t -put s i g n a l which i s a map of the l i g h t i n t e n s i t y v e r s u s p o s i t i o n i n p u t . Each time the r e a d i n g beam c r o s s e s spectrum 1, an e l e c t r o n i c gate sw i tches on i n t e g r a t o r 1 which produces and ho lds a s i g n a l p r o p o r t i o n a l to the l i g h t i n t e n s i t y i n the spec t rum, i n t e g r a t e d over the h e i g h t of the spec t rum. The same t h i n g happens wi th spectrum 2 and i n t e g r a t o r 2. Thus , i n one f u l l r a s t e r scan each i n t e g r a t o r produces up to 999 v o l t a g e p u l s e s , and the ampl i tude of each p u l s e c o r r e s p o n d s to the i n t e n s i t y of l i g h t f a l l i n g w i t h i n one s p e c t r a l e lement . The ampl i tude of each of the v o l t a g e p u l s e s i s d i g i t i z e d by the A/D c o n v e r t e r , and t h i s d i g i t i z e d output i s s t o r e d i n the core of the computer . The computer ou tputs the data onto magnet ic t a p e , p r o v i d e s an o s c i l l o s c o p e d i s p l a y of e i t h e r spectrum or t h e i r sum or d i f f e r e n c e , and r e l a y s v i t a l i n f o r -mation to the o b s e r v e r v i a the l i g h t d i s p l a y p a n e l . A f t e r one se t o f s p e c t r a i s r e c o r d e d , the r e a d i n g beam i s swi tched o f f f o r a v a r i a b l e p e r i o d o f time (the exposure t ime) to a l l o w l i g h t to aga in accumulate on the i s o c o n . A f t e r t h i s t i m e , the r e a d i n g beam aga in e x t r a c t s the s i g n a l , and the p r e c e d i n g p r o c e s s o c c u r s a g a i n . In t h i s way, enough s p e c t r a can be taken and e v e n t u a l l y added to produce a h igh s i g n a l - t o - n o i s e r a t i o . The i s o c o n thus has an i n t e g r a t i n g c a p a c i t y , s i n c e a l l the l i g h t f a l l i n g on the tube face d u r i n g the exposure 4 time c o n t r i b u t e s to the s i g n a l . The s a t u r a t i o n l e v e l can be c a l c u l a t e d from the data g iven by P . D . Nelson (1969) to be approx imate ly 1500 p h o t o - e l e c t r o n s per p i c t u r e e lement , where the p i c t u r e element i s 0.01 square m i l l i m e t e r . Assuming an e f f e c t i v e 10% quantum e f f i c i e n c y at 4000 A, t h i s means approx imate ly 15,000 photons are r e q u i r e d to s a t u r a t e one p i c t u r e e lement . G . A . H . Walker e t . a l . (1971) have d i s c u s s e d the no ise of the sys tem, and have shown i t to be comparable to p h o t o m u l t i p l i e r n o i s e . It i s p o s s i b l e to add s u c c e s s i v e exposures and o b t a i n a N^ improvement i n the s i g n a l - t o - n o i s e r a t i o , where N i s the number of e x p o s u r e s . It i s the purpose of t h i s t h e s i s to d e s c r i b e the image i s o c o n and a s s o c i a t e d e l e c t r o n i c s which were c o n -s t r u c t e d f o r i t s o p e r a t i o n by the a u t h o r , and to i n v e s t i g a t e the modula t ion t r a n s f e r f u n c t i o n of the s y s t e m . 5 THE ISOCON TUBE AND CAMERA The i s o c o n tube i s shown i n schematic form i n Figu r e 2. It i s d i v i d e d i n t o three main s e c t i o n s : the image s e c t i o n , the reading beam generation and scanning sec-t i o n , and the m u l t i p l i e r s e c t i o n . The image s e c t i o n c o n t a i n s a c i r c u l a r S-20 photo-cathode upon which the two s p e c t r a are imaged. Primary p h o t o - e l e c t r o n s , given o f f by the photocathode, are imaged onto the g l a s s t a r g e t by a c t i o n of the a x i a l e l e c t r i c and magnetic f i e l d s ( a 2.4:1 de m a g n i f i c a t i o n takes place onto the t a r g e t ) . The primary p h o t o - e l e c t r o n s cause the emission of secondary e l e c t r o n s from the t a r g e t . These secondary e l e c t r o n s are a t t r a c t e d to the t a r g e t mesh, l e a v i a q the t a r g e t with a p o s i t i v e charge p a t t e r n corresponding to the l i g h t i n t e n s i t y p a t t e r n on the photocathode« I t was found that i f the t a r g e t area i s cooled,to about 0°C. the charge p a t t e r n does not spread and the image remains sharp f o r exposure times of s e v e r a l minutes. The reading beam generation and scanning s e c t i o n c o n s i s t s of an e l e c t r o n gun, a c c e l e r a t i n g and f o c u s i n g e l e c t r o d e s , s t e e r i n g p l a t e s and separator, f o c u s i n g and alignment c o i l s , and x and y scanning c o i l s . The e l e c t r o n gun produces a beam of e l e c t r o n s which i s centered and focused onto the t a r g e t by a c t i o n of I S O C O N T U B E S C H E M A T I C F IELD 1/VV///////////77/FOCUS S ING COILS ///////////7777T/ l I U U R E 2 7 the alignment and f o c u s i n g c o i l s . The v a r i a b l e magnetic f i e l d of the x and y scanning c o i l s causes the e l e c t r o n beam to scan a square t e l e v i s i o n r a s t e r on the t a r g e t . T h i s e l e c t r o n beam i s turned on f o r one read-out frame (while data i s gathered) and remains on f o r s e v e r a l subsequent " e r a s i n g " frames (to f u l l y discharge the t a r g e t ) . Then the beam i s turned o f f f o r the exposure p e r i o d (while a charge p a t t e r n i s b u i l d i n g up on the t a r g e t ) . A -170 v o l t p o t e n t i a l on g r i d 1 accomplishes t h i s t u r n i n g o f f of the beam. Upon s t r i k i n g the t a r g e t , three t h i n g s happen to the e l e c t r o n s i n the beam: some land and n e u t r a l i z e the charge p a t t e r n ; some are d i r e c t l y r e f l e c t e d (the amount i n i n v e r s e p r o p o r t i o n to the charge on the t a r g e t ) ; and some are s c a t t e r e d (the amount i n d i r e c t p r o p o r t i o n to the charge on the t a r g e t ) . In the is o c o n scan, i t i s t h i s s c a t t e r e d r e t u r n beam which i s picked up by the e l e c t r o n m u l t i p l i e r , and the modulation of t h i s r e t u r n beam co n t a i n s the i n f o r -mation of the o r i g i n a l l i g h t p a t t e r n : the higher the s c a t -t e r e d r e t u r n beam the higher was the i n t e n s i t y of the l i g h t i n t h a t p a r t i c u l a r s e c t i o n of the scan. The f o u r s t e e r i n g p l a t e s and separator are used to separate the s c a t t e r e d p o r t i o n of the r e t u r n beam from the r e f l e c t e d p o r t i o n i n the f o l l o w i n g manner. A f t e r l e a v i n g the e l e c t r o n gun the e l e c t r o n beam t r a v e l s through the r a d i a l 8 e l e c t r i c f i e l d set up by the p o t e n t i a l d i f f e r e n c e on the s t e e r i n g p l a t e s . T h i s causes the forward beam to move i n a h e l i c a l t r a j e c t o r y toward the t a r g e t . A f t e r s t r i k i n g the t a r g e t , the r e f l e c t e d p o r t i o n o f the beam r e t u r n s i n a h e l i x o f o p p o s i t e p i t c h . The s c a t t e r e d p o r t i o n r e t u r n s i n a n o n -h e l i c a l p a t h . A f t e r aga in p a s s i n g through the s t e e r i n g p l a t e s on r e t u r n i n g from the t a r g e t , the r e f l e c t e d beam s t r i k e s the s e p a r a t o r wh i le the s c a t t e r e d beam passes through a ho le i n the s e p a r a t o r and s t r i k e s dynode 1 of the m u l t i p l i e r . The m u l t i p l i e r s e c t i o n i s a seven-dynode e l e c t r o n m u l t i p l i e r . The dynode m u l t i p l i c a t i o n produces a v i r t u a l l y n o i s e - f r e e a m p l i f i c a t i o n of the s c a t t e r e d beam s i g n a l . F i n a l output at the anode i s up to 10 microamperes . T h i s e l e c t r o n m u l t i p l i e r a m p l i f i c a t i o n a l l o w s f o r the use o f a l e s s s e n s i t i v e e x t e r n a l a m p l i f i e r . A f u l l e r d e s c r i p t i o n of the o p e r a t i o n o f the i s o c o n i s g iven by P . D . Nelson (1969) . The complete schemat ic diagrams o f the m o d i f i e d Marconi TF1709 camera and the master c o n t r o l u n i t c o n s t r u c t e d by the author f o r t h i s camera are g iven i n Appendix A . 9 THE VIDEO SIGNAL CIRCUITS The v ideo s i g n a l which appears at the anode of the e l e c t r o n m u l t i p l i e r i s a c u r r e n t s i g n a l wi th a t y p i c a l fo rm, as shown i n F i g u r e 3a . Only two l i n e scans are shown. There can be up to 999 l i n e s i n one f u l l v ideo f rame, depending on the s e t t i n g of the l o g i c c o n t r o l u n i t . The two p u l s e s i n each l i n e cor respond to the l i g h t i n t e n s i t y i n the two s p e c t r a . The p e d e s t a l on which the s p e c t r a l p u l s e s s i t c o r r e s p o n d s to the dark c u r r e n t from the f u l l photoca thode . Dur ing the r e t r a c e , the beam i s b lanked so there i s no c u r r e n t at these t i m e s . A l i n e scan takes 36.8 microseconds wi th about 8 microseconds of that t ime i n r e t r a c e . The d u r a t i o n o f the two s p e c t r a l p u l s e s depends on the he igh t o f each s p e c t r u m . The complete s i g n a l c i r c u i t i s shown i n F i g u r e 4 . The b a s i c v ideo a m p l i f i e r i s a Motoro la MC 1552 s e t at a v o l t a g e ga in of 100. I ts input , impedance i s 10K ohms. The anode s i g n a l i s coup led v i a c a p a c i t o r C , thus the low f r e -quency c u t - o f f f^ o f the a m p l i f i e r i s g iven by: f | " 2ttC x 10 4 Because the anode of the i s o c o n i s at +1400 v o l t s , c a p a c i t o r C must be a h igh v o l t a g e c a p a c i t o r and i t s c a p a c i t y must t h e r e f o r e be s m a l l ( l e s s than 0.05 m i c r o f a r a d ) . T h i s r e s u l t s i n a r e l a t i v e l y poor low f requency r e s p o n s e , with a t y p i c a l output v ideo s i g n a l as shown i n F i g u r e 3b. S ince no v i d e o clamp i s u s e d , there i s some " c r o s s - t a l k " from the spectrum 1 10 I S C C O N O U T P U T F I G U R E 3 A A M P L I F I E R O U T P U T F I G U R E 3B G A T E S FIGURE 3C I N T E G R A T O R O U T P U T FIGURE 3D VIDEO SIGNAL C IRCUIT FIGURE 4 12 pulse to the spectrum 2 pulse, because of the negative over-shoot in the spectrum 1 pulse. This i s e a s i l y held to a minimum (less than 1%) by appropriate choice of capacitor C and spectrum separation. The input diodes l i m i t the input voltage excursions during the turning on of the 1400 vo l t supply. The amplifiers T l and T2 are impedance matching emitter followers. T l couples the signal to the 75 ohm main cable. T2 couples the signal via two 50 ohm cables to the integrators. Their coupling time constants are set equal 4 to C x 10 seconds. The integrators, or "area detectors", are Chronetics Model 166. During the duration of each spectrel pulse, we open electronic gates which turn on these two signal integrators. The output of each integrator, which i s proportional to the area of i t s respective spectral pulse, i s held for 12 microseconds while i t i s d i g i t i z e d . The gates are shown in Figure 3c. Their duretion and separation can be set at the l o g i c control unit. The output of the integrators i s shown in Figure 3d. Since the logic control unit contains a l l TTL c i r c u i t r y , i t was necessary to modify the integrators s l i g h t l y to accept the +5 volt gate pulses, rather than the normal -700 m i l l i v o l t pulses. 13 THE MODULATION TRANSFER FUNCTION Of great significance in any spectral detection system i s resolution. But a more important and useful concept i s the modulation transfer function (MTF) or ampli-tude response as a function of input sine wave s p a t i a l frequency (cycles/millimeter). An easily understood method of measurement of MTF, which i l l u s t r a t e s the concept, i s as follows. Project test patterns which sinusoidally vary i n i n t e n s i t y onto the detector. Then plot the amplitude of the signal output of the detector as a function of the s p a t i a l frequency of the input test pattern. Figure 5a i l l u s t r a t e s the i n t e n s i t y input at three s p a t i a l frequencies, and Figure 5b i l l u s t r a t e s three corresponding t y p i c a l signal outputs. In Figure 5c, we see the MTF for the t y p i c a l detector, normalized to the largest s p a t i a l frequency. In almost a l l detectors, response decreases with increasing s p a t i a l frequencies. This method i l l u s t r a t e s the p r i n c i p l e s , but i s d i f f i c u l t to accomplish in practice. A more sati s f a c t o r y i n d i r e c t method w i l l be described l a t e r . The isocon, as with most detectors, has a decreasing response with increasing s p a t i a l frequencies. There are four main reasons for t h i s : imaging of photo-electrons onto the target, f i n i t e width of the reading beam, charge 14 T Y P I C A L D E T E C T O R M T F FIGURE 5A \J VJ \J i l l ! i ; i ; I* ! i MTF .0-FIGURE 5B 1.0 2.0 3.0 4.0 5.0 CYC./MM. FIGURE 5C 15 spread on the t a r g e t , and the t h e o r e t i c a l r e s o l u t i o n of the storage t a r g e t . The image s e c t i o n i s operated e x a c t l y as Marconi designed i t . The focus c o i l c u r r e n t i s 198 mi l l i a m p e r e s and the image focus c o i l c u r r e n t i s 68 m i l l i a m p e r e s . The o r b i t i n g c o i l s are connected as i n the camera diagram i n Appendix A i n order to center the image on the t a r g e t . We make adjustments i n the photocathode and g r i d 6 p o t e n t i a l s to provide the best r e s o l u t i o n . We must then r o t a t e the yoke s l i g h t l y so that our h o r i z o n t a l s p e c t r a are e x a c t l y p e r p e n d i c u l a r to the l i n e scans. A s l i g h t d i s t o r t i o n near the edges of the t a r g e t causes the s p e c t r a to appear 5-shaped, but t h i s i s because we scan the f u l l t a r g e t , and t h e r e f o r e see the more d i s t o r t e d edges which a smal l e r commercial scan does not see. The f u l l t a r g e t scan i s done to discharge the e n t i r e t a r g e t to prevent charge b u i l d - u p . The scanning c o i l s i n the reading beam s e c t i o n are l e f t running during the exposure time when the beam i s blanked. It was suggested t h a t perhaps t h i s o s c i l l a t i n g magnetic f i e l d was " s p i l l i n g " i n t o the image s e c t i o n causing a d e t e r i o r a t i o n of r e s o l u t i o n . We ran t e s t s to determine i f t h i s was t r u e . A t e s t p a t t e r n was p r o j e c t e d onto the isoc o n at a low l i g h t l e v e l and exposed f o r 150 seconds. During 8 frames we manually switched o f f the scanning c o i l s during the l i g h t exposure time, and switched them back 16 on f o r the reading and e r a s i n g of the t a r g e t . During another B frames with the same t e s t p a t t e r n on the i s o c o n , the scanning c o i l s were l e f t running as u s u a l . No d i f f e r e n c e between the two sets of output could be seen. Because of the d i f f i c u l t y of designing an automatic scan switch, we leave the scanning c o i l s o p e r a t i n g c o n t i n u o u s l y . Because of our method of sampling the t a r g e t with the reading beam, a d e f i n i t e upper l i m i t on the s p a t i a l frequency that can be detected i s set by the Nyquist c r i t e r i a . No frequency g r e a t e r than one-half the sample ra t e ( i . e . , the number of scan l i n e s per m i l l i m e t e r ) may be detected without a l i a s i n g . However, the e l e c t r o n beam which does t h i s sampling i s not i n f i n i t e s i m a l l y s m a l l , but of f i n i t e width. Now i f the sample r a t e i s set so that the width of the reading beam i s g r e a t e r than the l i n e s e p a r a t i o n , then t h i s broad reading beam w i l l act as an analog f i l t e r . The exact s p a t i a l frequency c h a r a c t e r i s t i c s of t h i s e f f e c t i v e f i l t e r are d i f f i c u l t to analyze t h e o r e t i c a l l y , s i n c e they are dependent on the energy d i s t r i b u t i o n i n the beam. A reasonable i d e a of the beam width can be gotten from examining Figure 6. This i s a graph of s i g n a l output from the isocon f o r a constant l i g h t i n p u t , versus s e p a r a t i o n of the l i n e scans on the t a r g e t and photocathode. As the l i n e scan s e p a r a t i o n i n c r e a s e s , the s i g n a l w i l l a l s o i n c r e a s e R E L A T I V E SIGNAL 5 4 3-2 30 SCAN SEPARATION ON PHOTOCATHODE 60 90 120 |&o 180 210 240 ( uM) i i i i i i i ' i • • i 20 40 60 80 100 (yuM) SCAN SEPARATION ON TARGET F I G U R E 6 18 ( s i n c e each scan discharges a l a r g e r p o r t i o n of the t a r g e t ) , u n t i l the beam no longer o v e r l a p s the area scanned by the previous beam. At t h i s s e p a r a t i o n , an i n c r e a s e i n the scan s e p a r a t i o n does not in c r e a s e the s i g n a l . Over the f u l l range of separations p o s s i b l e with our c o n t r o l set-up, however, no l e v e l l i n g o f f i n s i g n a l was n o t i c e d , which i n d i -c ates that the beam width i s g r e a t e r than 90 microns on the t a r g e t (220 microns on the photocathode). Since the maximum l i n e scan s e p a r a t i o n which i s used i n normal o p e r a t i o n i s 170 microns on the photocathode, i t i s u n l i k e l y that a l i a s i n g w i l l o ccur. Charge spread and consequent image smearing can occur on the t a r g e t because the g l a s s of which the t a r g e t i s made has a l e s s - t h a n - i n f i n i t e r e s i s t a n c e . I t i s t h i s charge spread which sets the maximum exposure time p o s s i b l e with the i s o c o n . In order to i n c r e a s e the r e s i s t a n c e o f the t a r g e t , we must r e f r i g e r a t e the tube, e s p e c i a l l y i n the t a r g e t area. A c l o s e d , f o r c e d convection c o o l i n g system i s used which passes a i r cooled by dry i c e between the tube and the f o c u s i n g c o i l s . Temperatures at the t a r g e t area of the isocon tube can be maintained between 4°C and -15°C. The MTF as a f u n c t i o n of temperature w i l l be seen l a t e r i n t h i s chapter* Because the reading beam i s s c a t t e r e d by the p o t e n t i a l p a t t e r n on the beam side of the t a r g e t , there i s a t h e o r e t i c a l l i m i t of r e s o l u t i o n due to the t r a n s f o r m a t i o n 19 of the charge p a t t e r n on the photocathode s i d e of the t a r -get to the p o t e n t i a l p a t t e r n on the r e a d i n g beam s i d e . T h i s l i m i t i n g r e s o l u t i o n i s d i s c u s s e d by I .M. Kr i t tman (1963) . He g i v e s the s i n e wave response (MTF), n o r m a l i z e d to a s p a t i a l f requency o f 0, as a f u n c t i o n o f f u l l c y c l e s / m i l l i m e t e r (N): -2 Nt , -2 N ( t , + 2 t , ) MTF (N) = e - e x * 4 N t 2 where: t^ = t a r g e t t h i c k n e s s ( in m i l l i m e t e r s ) t 2 = t a r g e t m e s h - t o - t a r g e t s p a c i n g ( i n m i l l i m e t e r s ) . _3 For the i s o c o n with a t a r g e t t h i c k n e s s of 2 x 10 m i l l i m e t e r s and a t a r g e t m e s h - t o - t a r g e t s p a c i n g of 0.75 m i l l i m e t e r , the t h e o r e t i c a l upper l i m i t of MTF i s shown i n F i g u r e 7. In t h i s p l o t we n o r m a l i z e d the MTF to u n i t y at a s p a t i a l f r e -quency of 0.046 c y c l e s / m i l l i m e t e r . Because of the wide t a r -g e t - t o - t a r g e t mesh s p a c i n g and t h i n t a r g e t , a very low MTF would r e s u l t , i f one c o n s i d e r e d o n l y the Kr i t tman a s s u m p t i o n s . The f i n a l MTF i s a composi te o f the above f o u r f a c t o r s . The t h e o r e t i c a l r e s o l u t i o n o f the t a r g e t i s a f u n c t i o n o f tube geometry a lone and s e t s a b a s i c upper l i m i t on the MTF, a l t h o u g h , as we s h a l l s e e , the upper l i m i t i s much h i g h e r than tha t suggested by a s imple Kr i t tman a n a l y s i s . Beam width and image s e c t i o n r e s o l u t i o n are a f u n c t i o n of both tube geometry and o p e r a t i n g c o n d i t i o n s , but are assumed to be independent o f t a r g e t temperature and exposure t i m e . It i s t h e r e f o r e the p r a c t i c e to s e t up the tube p o t e n t i a l s f o r the bes t r e s o l u t i o n f o r a s h o r t exposure 20 F I G U R E 7 21 time (when there i s l i t t l e charge spread), and assume t h a t the lowering of MTF with exposure time i s p r i m a r i l y a r e s u l t of charge spread. I t i s the charge spread which shows i t s e f f e c t as a f u n c t i o n of time and temperature. A method of measuring the MTF of the isocon was designed which would e l i m i n a t e the need f o r d i f f i c u l t - t o -produce t e s t p a t t e r n s and high q u a l i t y o p t i c s . F i g u r e 8 i l l u s t r a t e s the t e s t set-up. The l e n s i s at a d i s t a n c e equal to i t s f o c a l length from the p i n h o l e , which has a diameter of 0.5 m i l l i m e t e r . T h i s r e s u l t s i n almost p a r a l l e l l i g h t at the photocathode of the i s o c o n . The t e s t p a t t e r n i s f i x e d d i r e c t l y to the face p l a t e , and the face p l a t e i s 2.49 m i l l i m e t e r s t h i c k . Thus the photocathode i l l u m i n a t i o n i s p r o p o r t i o n a l to the t e s t p a t t e r n transparency. The e n t i r e t e s t set-up was placed i n a l i g h t - t i g h t box„ The t e s t p a t t e r n c o n s i s t s of four p a i r s of s l i t s . The dimensions are given i n Figure 9a. One s l i t i n each p a i r was covered with a f i l m . Thus the "spectrum" pro-duced appeared as four p a i r s of emission l i n e s , with the l i n e s t r e n g t h r a t i o of each p a i r a c o n s t a n t . The l i n e p a i r s are assumed to have the i n t e n s i t y p r o f i l e of Figure 9b. T h i s p r o f i l e as a f u n c t i o n of p o s i t i o n i s i ( x ) . Now i ( x ) i s convolved with the t r a n s f e r f u n c t i o n of the isocon d e t e c t i o n system h(x) to produce the output o ( x ) . M T F T E S T S E T T E S T P A T T E R N L E N S I S O C O N C A M E R A P H O T O C A T H O D E FIGURE 8 P I N H O L E L A M P DI F F U S I N G S C R E E N 23 <X> vc ro rO T E S T P A T T E R N ( M M . U N I T S ) CD — fO i 1 2 . 6 4 0 in rO CM in 1 2 . 6 4 5 o r-1 2 . 7 0 9 2 . 2 1 7 2 . 0 6 0 2 . 5 3 4 2 . 4 7 4 F I G U R E 9 A I N T E N S I T Y P A T T E R N n >- x F I G U R E 9 B 24 i ( x ) * h(x) = o(x) Now taking F o u r i e r transforms and appl y i n g the c o n v o l u t i o n theorem: I(N) x H(N) = 0(N) where the c a p i t a l s denote the transform and N i s the s p a t i a l frequency. Remember that these transforms are complex. The MTF of the system i s simply the amplitude p o r t i o n (or modulus), of the complex transform H(N). So we can f i n d the MTF by the f o l l o w i n g : M T F = M 0 D (H(N)) . «gg The general experimental procedure went as f o l l o w s . The isocon was set up i n the l i g h t - t i g h t box with the t e s t p a t t e r n , and cooled to a s p e c i f i c temperature. The temper-ature was held constant and monitored on a ch a r t r e c o r d e r . The l i g h t was turned on and adjusted to give the d e s i r e d s i g n a l l e v e l at the p a r t i c u l a r exposure time used. Gate 2 was set at 1.2 microseconds d u r a t i o n and timed to c o i n c i d e with the cente r of the 3.2 microsecond s i g n a l pulse (from the 9.1 m i l l i m e t e r high s l i t s ) . The s i g n a l from i n t e g r a t o r 1 during gate 1 was not used. The s i g n a l was read i n the usual manner and the data recorded on magnetic tape at the end of each exposure time. The beam remained on f o r an a d d i t i o n a l f i v e frames a f t e r read-out, to f u l l y discharge the t a r g e t . A block of data of up to 50 read-outs was taken f o r each p a r t i c u l a r exposure time, temperature, and l i g h t l e v e l used. A f t e r each block of data was taken, the 25 pinhole was covered and a block of about 50 read-outs of the "dark c u r r e n t " was taken. The tapes of data were read, each block was averaged, and the a p p r o p r i a t e averaged "dark c u r r e n t " was s u b t r a c t e d , using e x i s t i n g programs, on the IBM 360 computer at the computer c e n t e r of the U n i v e r s i t y of B r i t i s h Columbia. Each averaged block was s t o r e d i n a f i l e on the data c e l l . Only the center 450 l i n e s were s t o r e d (out of 990 l i n e s used). Figure 10 shows a p l o t of the output of a t y p i c a l f i l e . The sample r a t e can be found by counting the number of p o i n t s between the c e n t e r s of the s l i t s . We a l s o assume that the l i g h t i n t e n s i t y was i n the l i n e a r range of the i s o c o n , i f the r a t i o of the pulse heights i n a pulse p a i r was the a p p r o p r i a t e constant. As the l i g h t i s i n t e n s i f i e d , and t a r g e t s a t u r a t i o n occurs, t h i s r a t i o becomes u n i t y . F o l l o w i n g the p r e v i o u s l y o u t l i n e d method, two computer programs were w r i t t e n to determine the MTF from the data i n f i l e s . The f i r s t program generated an input pulse p a i r i ( x ) i n accordance with the t e s t p a t t e r n s l i t dimensions and d e n s i t i e s , and c a l c u l a t e d the d i s c r e t e F o u r i e r transform, I(N). In order to avoid a l i a s i n g , a sample r a t e ten times g r e a t e r than that used on the output o ( x ) , was used on i ( x ) . The modulus of I(N) f o r a l l values of N up to the Nyquist frequency of the b a s i c sample 26 T E S T P A T T E R N O U T P U T 0.0 10.0 20.0 30JJ L I N E ( X l O 1 ) 40.0 50 F I G U R E 10 27 r a t e was s t o r e d i n a f i l e . The second program read from the data f i l e s a s e l e c t e d output pulse p a i r o(x) and c a l c u l a t e d i t s d i s c r e t e F o u r i e r transform 0(N), and took i t s modulus. Th i s same program a l s o smoothed the r e a l p a r t s of both I(i\!) and 0(N) by c o n v o l v i n g each with a smoothing f u n c t i o n ( i n a l l cases a seven p o i n t wide t r i a n g l e ) and d i v i d e d Mod 0(N) by Mod I(N) to produce a smooth MTF. T h i s MTF was then normalized to the lowest non-zero value of N and s t o r e d i n a f i l e . F i g u r e 11 i l l u s t r a t e s with p l o t s the e n t i r e p r o c e s s . In a l l cases, transforms were taken over 128 p o i n t s i n the data. The sample r a t e f o r the c e n t e r two pulse p a i r s (pulse p a i r s 2 &. 3) was 5.95 - 0.05 samples per m i l l i m e t e r . Because of a s l i g h t n o n - l i n e a r i t y i n the scanning c i r c u i t s , the sample r a t e was about Q% g r e a t e r f o r the outer two pulse p a i r s . Thus f o r pulse p a i r s 2 &. 3, the Nyquist frequency was 2.97 c y c l e s per m i l l i m e t e r and the lowest frequency examined was 0.046 c y c l e s per m-illimeter. In order to e l i m i n a t e the e f f e c t s of systematic e r r o r s i n t h i s method, the t r a n s f e r f u n c t i o n s found i n the above manner f o r the center two pulse p a i r s were averaged at each s p a t i a l frequency. T h i s averaged MTF i s assumed to be the t r a n s f e r f u n c t i o n over the c e n t r a l r e g i o n of the photocathode. A t h i r d program was w r i t t e n to do t h i s averaging, give standard d e v i a t i o n s , and make p l o t s of the r e s u l t s with the standard d e v i a t i o n e r r o r bars. The outer M T F M E A S U R E M E N T P R O C E S S T A K E N F R O M T A P E S O F I S O C O N O U T P U T M O D (O(N)) M O O T H E D M O D (O(N)) t i uurtt I I 29 two pulse p a i r s were not examined i n d e t a i l , because the gr e a t e r sample rate made comparison d i f f i c u l t . The most important r e s u l t s are shown i n F i g u r e s 12-14 and l i s t e d i n Tables 1-9. The MTF as a f u n c t i o n of s p a t i a l frequency i s given f o r v a r i o u s temperatures, exposure times, and l i g h t l e v e l s , out to the s p a t i a l frequency at which the standard d e v i a t i o n i n MTF became 25%, F i g u r e 12a (Table 1) shows the MTF taken at a l i g h t l e v e l of about h a l f the s a t u r a t i o n l e v e l . F i g u r e 12b (Table 2) i s the MTF at a s i g n a l l e v e l of about one-quarter of that i n Figure 12a (but at the same exposure time and t a r g e t temperature). The MTF at the low l i g h t l e v e l i s s i g n i f i c a n t l y d e t e r i o r a t e d . T h i s produces a n o t i c a b l e broadening near the base of the emission l i n e s , i n l i n e s p e c t r a . T h i s dependence of MTF on s i g n a l l e v e l made i t necessary to measure a l l MTFs at the same s i g n a l l e v e l i n order to i n s u r e a proper comparison among v a r i o u s temperatures and exposure times. T h e r e f o r e , a l l the f o l l o w i n g t r a n s f e r f u n c t i o n s were measured at the same s i g n a l l e v e l , corresponding to about h a l f the s a t u r a t i o n v a l u e . Figure 13 (Tables 1, 3-6) shows the MTF at v a r i o u s exposure times, from 17.0 seconds to 298 seconds, with the t a r g e t temperature at -15°C. Thi3 i s the lowest t a r g e t 30 temperature that can be reached. Figure 14 (Tables 7-9) shows the MTF at three exposure times, from 17.0 seconds to 77 seconds, with the t a r g e t temperature at 0°C. 31 M T F A S A FUNCTION CF LIGHT L E V E L o i 03 a ' to 2 1 a CM a ' a a i I I I i :-l ' I ' I . . 'Hi... 1 n 1 1 i 0.0 0.4 0.8 1.2 1.6 2.0 CYC /MM FIGURE I2A 32 M T F A S A F U N C T I O N O F L I G H T L E V E L o to I I I I 2 H M i l l Q 1 1 1 1 1 1 0.0 0.4 0.8 1.2 1.6 2.0 CYC /MM F I G U R E I2B 3 3 M T F AT -15° C EXP. TIME 17 SEC. o i x 0 3 I I I I in a I CM o ' CD — -I J T ''Hi.,, o | I | 1 1 1 0-0 0.4 0.8 1.2 1.6 2.0 C Y C / M M F IGURE I3A 34 0 3 U 3 a ' I I I r i MTF AT - I 5 ° C E X P . T I M E 35 S E C . • i I 1 1 1 1 1 0.0 0.4 0.8 1.2 1.6 2.0 CYC /MM FIGURE I3B 35 M T F AT - I 5 ° C E X P . T I M E 77 S E C . » » ' 1 I T 1 I I I * ' 1 1 1 0.8 K2 CYC/MM FIGURE I3C 36 oo U3 21 a CM ''1 a I I 0 .0 0 .4 M T F A T -I5°C E X P . T I M E 151 S E C . 0 .8 1.2 crc/MM F I G U R E I 3 D 37 cn 10 o - A 1 2 1 ° I j I I I • a ' a a M T F AT -I5°C EXP. TIME 298 SEC. 1 i . 1 11 1 1 1 1 1 0.0 0.4 0.8 1.2 1.6 2.0 CYC /MM FIGURE I3E 38 M T F A T 0°C E X P . TIME 17 S E C . I I I I 1 \ i i i ' 11 i • • • * 1 1 1 1 1 0.0 0.4 0.8 1.2 1.6 ZJJ CYC /MM F I G U R E I4A MTF AT C°C EXP TIME 3 5 S E C as a ' 10 i tM I I f ' l , ' M I 1 1 1 1 1 0.0 0.4 0.8 1.2 1.6 2.0 C Y C / M M FIGURE I4B 40 M T F AT C°C E X P . T I M E 77 S E C . 0 3 to 21 a CN I a i i 1 « I i . . . . i , , 1 1 1 0.0 0.4 0.8 1.2 1.6 2.0 CYC /MM FIGURE I4C TABLE 1 MTF a t - 1 5 ° C , Exposure time 17. seconds , medium l i g h t l e v e l . FREQUENCY PULSE2 MTF PULSE3 MTF AVERAGE MTF S T A N D . D E V . 1 0 .046492 1.000000 I . 0 0 0 0 0 0 I . 0 0 0 0 0 0 0 . 0 2 0 .092984 0 .964462 3 . 9 7 8 7 3 5 0 . 9 7 1 5 9 9 0 . 0 1 0 0 9 2 3 0.139477 0 .914994 0 . 9 2 9 4 6 5 0 . 9 2 2 2 2 9 0 . 0 1 0 2 3 2 4 0 . 1 8 5 ? 6 9 0 .838861 0 . 8 4 7 2 3 6 0 . 8 4 304 8 0 . 0 0 5 9 2 2 5 0 .232461 0 .809816 3 . 7 8 8 7 0 6 D.799261 0 . 0 1 4 9 2 8 6 0 .278953 0 . 7 7 8 1 4 5 0 . 7 4 4 3 1 4 0 . 7 6 1 2 3 0 0 . 0 2 3 9 2 2 7 0 . 3 2 5 4 4 5 0 . 7 4 2 5 0 3 0.715650 0 . 7 2 9 0 7 6 3 . 0 1 8 9 8 8 8 0 . 371937 0 . 7 0 5 7 8 2 0 . 6 9 1 3 6 3 0 . 6 9 8 5 7 2 0 . 0 1 0 1 9 6 9 0 . 4 1 8 * 3 0 0 . 6 6 5 9 2 9 0 . 6 6 4 5 2 4 0 . 6 6 5 2 2 6 0 . 0 0 0 9 9 4 10 0 . 4 6 4 9 2 2 0 .629864 0 . 6 3 1 8 8 7 0 . 6 3 0 8 7 5 3 . 0 0 1 4 3 0 11 0 . 5 1 1 4 1 4 0 .599172 0 . 5 8 5 9 6 3 0 . 5 9 2 5 6 7 0 . 0 0 9 3 4 0 12 0 .557906 0 .579031 3 . 5 4 1 5 7 0 3 . 5 6 0 3 0 5 0 . 0 2 6 4 8 3 13 0 .604398 0 .561270 0 . 5 0 9 5 6 2 0 . 5 3 5 4 1 6 0 . 0 3 S 5 S 3 14 0 .650890 0 . 5 2 9 1 3 8 0 . 4 8 7 9 6 7 0 . 5 0 8 5 5 2 0 . 0 2 9 1 1 2 15 0 .697383 0 .487151 3 . 4 7 0 7 3 1 3 . 4 7 8 9 4 1 0 . 0 1 1 6 1 1 16 0 .743875 0 . 4 4 3 1 7 7 0 . 4 5 6 8 7 8 3 . 4 5 0 0 2 8 0 . 0 0 9 6 8 8 17 0 . 7 9 0 3 6 7 0 . 4 0 2 6 9 9 0 . 4 4 4 7 3 4 0 . 4 2 3 7 1 6 3 . 0 2 9 7 2 3 18 0 . 8 3 6 8 5 9 0 . 3 6 9 6 4 8 0 . 4 2 0 7 4 7 0 . 3 9 5 1 9 7 0 . 0 3 6 1 3 3 19 0 .883351 0 .345104 3 . 3 9 3 8 1 4 0 . 3 6 9 4 5 9 0 . 0 3 4 4 4 3 20 0 . 9 2 9 8 4 4 0 . 3 3 1 5 6 6 0 . 3 6 9 5 6 8 0 . 3 5 0 5 6 7 3 . 0 2 5 B 7 2 21 0 . 9 7 6 3 3 6 0 . 3 2 8 9 6 7 3 . 3 4 4 6 3 9 0 . 3 3 6 8 0 3 0 . 0 1 1 0 8 2 22 I. 022027 0 .313 906 3 . 3 2 2 6 2 9 3 . 3 1 8 2 6 8 0 . 0 0 6 1 6 9 23 1 .069320 0 . 2 8 4 6 0 9 0 . 3 0 3 8 7 3 0 .294241 0 . 0 1 3 S 2 1 24 1. 115812 0 . 2 5 2 6 4 9 0 . 2 9 5 1 0 0 0 . 2 7 3 8 7 5 0 . 0 3 0018 25 1 .162304 0 .219551 3 . 2 9 8 1 4 9 3 . 2 5 8 8 5 0 0 . 0 5 5 5 7 7 26 1 .208797 0 .197473 0 . 29443 9 0 . 2 4 5 9 5 6 0 . 0 6 8 5 6 5 2 7 I . 255288 0 . 1 8 9 0 6 6 0 . 2 8 1 5 0 4 0 . 2 3 5 2 8 5 3 . 0 6 5 3 ' J 4 28 1. 301 781 0 . 1 8 7 6 5 5 0 . 2 5 2 9 7 9 0 . 2 2 0 3 1 7 0 . 0 4 6 1 9 I 29 1 .348272 0 .200158 0 . 2 1 2 8 3 1 0 . 2 0 6 4 9 4 0 . 0 0 8 9 6 I 30 I . 394765 0 .208032 0.187666 0 .197 84 9 3 .014401 31 1 .441257 0 . 1 9 2 2 3 6 0 . 187384 ' 0 . 189810 0 . 0 0 3 4 31 32 1 .487749 0 .172211 3 . 217992 3 . 1 9 5 1 0 1 0 . 0 3 2 3 7 2 33 1 .534242 U . L4t>964 0 . 2 6 5 2 0 0 0 . 2 0 5 5 8 2 D.0843 12 TABLE 2 MTF a t - 1 5 ° C , E x p o s u r e t ime 17 s e c o n d s , low l i g h t l e v e l . FREQUENCY PULSE2 MTF PULSE3 MTF AVE* AGE MTF STAND. DEV, 1 0 .046492 1.000000 I . 0 0 0 0 0 0 1 .000000 0 .0 2 0 .092984 0 .930168 0 .934666 3 .932417 3 .003181 3 0. 139<.77 0 .819016 3 . 8 0 9 8 3 8 0 .814427 0 . 0 0 6 4 9 0 4 0. 185969 0 .646437 3 .620855 3 .6336^6 0 . 0 1 8 0 8 9 5 0 .232461 0.569363 0 . 5 2 9 0 2 9 3.549196 3.328521 6 0 .278953 0 .512162 3 .471195 0 .491678 0 .028 95K 7 0 .325445 0 .478026 3 . 4358^9 3 .456938 3 .029824 8 0 .371937 0 .451969 0 .410622 0 .431296 3.029236 9 0 .418430 0 .423622 0 . 3 6 5 4 B 7 0 .404554 0 .026965 10 0.464922 0.40 32 63 3 .366028 3 .384645 3 . 0 2 6 3 2 9 11 0 .511414 0.381951 0 .33870? 3 .360327 0 .030582 12 0 .557906 0 .363929 0 . 3 0 8 5 1 7 3 .336223 3 .339192 13 0.604398 0 .349310 3 . 2 8 3 3 8 9 0 . 3 1 6 3 4 9 3 .046613 14 0 .650890 0 .3176 73 3 .260432 3 .289053 0 .040475 15 0 .697383 0.2 8 702 8 0 .245493 0 .2662S I 3 .029370 16 0 .743875 0 .260561 3 . 2 3 7 9 1 4 0 .249238 0 .016014 17 0 .790367 0.231563 3 .241161 3 .23636? 3 .006787 18 0 .836859 0 .213464 0 . 2 3 8 5 0 6 0 .2?5935 3 .017707 19 0.883351 0 .203745 0 . 2 2 7 4 1 0 0 .215577 0 .016733 20 0.929844 0.195961 3 .214577 3 .205269 0 .013164 21 0 .976336 0 .200939 0 . 2 0 4 4 8 0 3 .202709 3 .002504 22 1.022827 0.192861 0 .200296 3 .196579 3 .005258 23 1 . 069320 0 .173336 0 . 196464 0. 184900 3 .016354 24 1.115812 0.152722 3.191 712 3 .172217 3 . 027570 25 I. 162304 0 .137860 0 . 1 7 6 0 9 ? 3 .156975 3 .327034 26 1.208797 0 .124789 3 .160612 0. 142700 0 .025 331 27 1.255288 0 .112655 3 .14963 5 3 .131145 0 . 0 2 6 1 4 9 28 1.301781 0 .108739 0 .146882 0.1 2781 I 3 .02S9 7 1 29 1.348272 0 .102325 0 . 1 5 8 0 7 5 0 . 1 3 0 2 0 0 0.03 94 21 30 1.394765 0.102821 3 .18383 I 3 .143326 0 .057282 31 1.441257 0.106041 0 .235012 3 .170526 0 . 0 9 1 1 9 6 TABLE 3 MTF at - 1 5 ° C , Exposure time 35 seconds , medium l i g h t l e v e l . FREQUENCY PULSE2 MTF PULSE 3 MTF AVE* AGE MTF STAND. DE Vi 1 0.046492 1.000000 I.000000 I .000000 0.0 2 0.092984 0.938162 0.936862 0.937511 3.000919 3 0 . 139477 0.841406 0.825208 0.833307 0.01 1454 4 0.185969 0.707416 3.688902 3.698159 0.013092 5 0.232461 0.637697 0.622279 3.629988 0.010902 6 0.278953 0.586706 0.584147 0.585426 0.0018 09 7 0.325445 0.547267 3.560257 3.553762 0.009186 8 0.371937 0.511547 0.53 4216 3.522881 0.016030 9 0.418430 0.473967 0.503873 0.488920 3.021147 10 0.464922 0.442054 3.464240 0.453147 0.015688 11 0.511414 0.414175 3.418193 3.416184 0.002841 12 0.557906 0.388847 0.378587 3.3 83 717 3.007255 13 0.604398 0.362293 3.351984 0.357139 0.0072B9 14 0.650890 0.331014 3.334780 3.332897 3.002663 15 0.697383 0.303670 3.315437 0.309554 0.003321 16 0.743875 0.277957 0 .295508 0.286732 0.012410 17 0.790367 0.256241 0 .273694 3.264967 0.012341 18 0.836859 0.235397 0.239688 3.237542 0.003034 19 0.883351 0.212153 0.214879 3.213516 3.001927 20 0.929844 0.189884 0.198896 0. 194390 0.006372 21 0.976336 0.172671 3.181158 3.176915 0.006001 22 1.022827 0. 156953 0. 172181 3.164557 3 .0107S8 23 1.069320 0.142383 0.165564 0.153974 0.016392 24 1.115812 0.126236 3 .159785 3.143011 0.023723 25 1.162304 0. 103542 0.159951 3.131746 0.039887 26 1.208797 0.083526 0.161888 0. 12270 7 0.055410 27 1.255288 0.065001 0.161140 3.113070 3.067980 TABLE 4 MTF at - 1 5 ° C , Exposure time 77 seconds , medium l i g h t l e v e l . FREQUENCY PULSE2 MTF PUL SF3 MTF AVERAGE MTF ST AMD.DEV 1 0 .046492 1 .000000 I . 0 0 0 0 0 0 I . 000000 0 . 0 2 0 .0929a4 0 . 9 30 8 82 0 . 9 4 7 8 0 1 3 . 9 3 9 3 4 1 3 . 0 1 1 9 6 3 3 0 . 139477 0 . 8 2 4 1 1 9 0 .842 03 0 3 .833074 0 . 0 1 2 6 6 5 4 U .185969 0 .664921 0 .687761 3 .676341 3 . 0 1 6 1 5 0 5 0 .232461 0 . 6 0 4 1 5 7 0 . 6 1 0 4 4 0 0 . 6 0 72 98 0 . 0 0 4 4 4 3 6 0 .278953 0 . 5 5 0 1 5 9 3 . 5 5 6 9 8 4 3 . 5 5 3 5 7 1 0 . 0 0 4 8 2 6 7 0 . 3 2 5 4 4 5 0 .511162 0 . 5 2 5 2 7 5 3 . 5 1 8 2 1 8 3 . 0 0 9 9 7 9 8 0 . 3 7 1 9 3 7 0 .477435 D . 4 9 8 2 6 7 0 . 4 8 7 8 5 1 0 . 0 1 4 7 3 1 9 0 .418430 0 .438461 3 . 4 5 9 5 8 6 3 . 4 4 9 0 2 3 3 . 0 1 4 9 3 7 10 0 .464922 0 .402983 0 . 4 1 2 1 5 5 0 . 4 0 7 5 S 9 0 .OOS485 11 0 . 5 1 1 4 1 4 0 .368262 0 . 3 5 5 9 6 0 0 . 362111 0 . 0 0 8 6 9 9 12 0 .557906 0 . 3 3 7 4 8 7 0 . 3 0 7 2 9 6 3 . 3 2 2 3 9 1 3 . 0 2 1 3 4 8 13 0 .604398 0 . 3 0 3 6 3 9 0 .274581 3 . 2 8 9 1 1 0 0 . 0 2 0 5 4 7 14 0 . 6 5 0 8 9 0 0 .274621 0 .2 5302 2 0 . 2 6 3 8 2 2 3 . 0 1 5 2 7 2 15 0 .697383 0 . 2 4 4 0 9 3 0 .231 709 0 . 2 3 7901 3 . 0 0 8 7 5 7 16 0 . 7 4 3 8 7 5 0 . 2 1 3 5 1 6 3 . 2 1 2 8 8 9 3 . 2 1 3 2 0 2 0 . 0 0 0 4 4 3 17 0 . 7 9 0 3 6 7 0 .189934 0 . 1 9 3 6 7 7 3 . 1 9 1 8 0 6 3 . 0 0 2 6 4 5 18 0 . 8 3 6 8 5 9 0 . 1 6 8 0 7 8 3 . 1 7 2 0 9 1 0 . 1 7 0 0 8 4 0 . 0 0 2 8 3 8 19 0 .883351 0 . 1 5 1 9 8 7 3 . 1 5 7 5 1 8 3 . 1 5 4 75 3 0 . 0 0 3 9 1 1 20 0 .929844 0 . 143325 0 . 1 4 8 2 2 6 3 . 145775 3 . 0 0 3 4 b 6 21 0 . 9 7 6 3 3 6 0 . 1 3 52 64 0 . 144397 0 . 1 3 9 8 3 0 0 . 0 0 6 4 5 8 22 1. 022827 0 .124021 3 . 139122 3 . 1 3 1 5 7 2 0 . 0 1 0 6 7 7 23 1 .069320 0. 107491 0 . 1 3 3 4 6 2 3 . 1 2 0 4 7 6 0 . 0 1 8 3 6 5 24 1 .115412 0 . 0 8 9 2 9 7 3 . 1 2 6 3 7 4 3 .107835 3 . 0 2 5 2 1 7 25 1.162 304 0 .080230 0 . 112638 0 . 0 9 6 4 3 4 0 . 0 2 2 9 1 6 26 1 .208797 0 .074843 3 . 1 0 8 4 2 4 3 . 0 9 1 6 3 3 0 . 0 2 3 7 4 6 27 1 .255288 0 . 0 7 6 5 5 0 3 . 1 0 6 5 8 3 3 . 0 9 1 5 6 6 3 . 0 2 1 2 3 7 28 1.301781 0 . 0 8 7 3 7 4 0 . 1 0 0 5 2 2 0 . 093948 0 . 0 0 9 2 9 7 29 1 .348272 0 .093258 3 . 100652 3 . 0 9 6 9 5 5 0 . 0 0 5 2 2 8 30 I .394765 0 . 0 9 3 7 2 9 0 . 1 0 5 3 3 9 3 . 0 9 9 5 3 4 3 . 0 0 8 2 1 0 31 1 .441257 0 . 0 7 8 6 4 7 3 . 118530 0 . 0 9 8 5 8 9 0 . 028201 32 1 .487749 u . 0 6 0 9 1 7 3 . 146083 3 . 1 0 3 5 0 0 0 . 0 6 0 2 2 1 / TABLE 5 MTF at -15 °C, Exposure time 151 seconds, medium l i g h t l e v e l . FREUUEMCY PULSF2 MTF PULSE3 MTF AVERAGE MTF ST AMD.DEV 1 0.046492 1.000000 I .000000 1.000000 0.0 2 0.092984 0.953566 0.952424 3.952995 3.000807 3 0.139477 0.869226 0.853038 3.861132 0.011447 4 0.185969 0.730865 0.711359 0.721112 3.013/93 5 0.232461 0.632821 0.619852 0.626337 0.009171 6 0.278953 0.549979 3 .559223 3.554601 0.006536 7 0.325445 0.494991 0.521677 3.5083 34 3.3188/0 8 U.371937 0.450959 3.488894 0.469926 0.026824 9 0.418430 0.410542 3.451035 3.430789 3.028633 10 0.464922 0.375655 0.407670 3.391662 0.022S38 l l 0.511414 0.342477 3.356813 0.34964 5 0.010137 12 0.557906 0.312342 0.31072 5 3.311534 3.001144 13 0.604398 0.281950 0.281011 3.281481 0.000664 14 0.650890 0.248280 0.262777 3.255528 0.0102>1 15 0.697383 0.213463 0.247288 0.230376 0.02 3918 16 0.743875 0.184206 3.236979 3.210592 0.037316 17 0.790367 0.155491 0.228912 3.192201 3 .051915 18 0.836859 0.130319 0.209263 0.169791 0.055822 19 0. 883351 0.113515 3.189475 3.151495 0.053712 TABLE 6 MTF a t - 1 5 ° C , E x p o s u r e t i m e 298 s e c o n d s , medium l i g h t l e v e l . FREQUENCY PUL SE 2 MTF PUL SE 3 MTF AVERAGE MTF S T A N D . D E V 1 0 . 0 4 6 4 9 2 1 . 0 0 0 0 0 0 1 . 0 0 0 0 0 0 1 . 0 0 0 0 0 0 0 . 0 2 0 . 0 9 2 9 8 4 0 . 9 3 0 9 7 2 3 . 9 3 6 4 7 5 3 . 9 3 3 7 2 3 0 . 0 0 3 8 9 1 3 0 . 1 3 9 4 7 7 0 . 8 0 7 5 8 2 0 . 8 0 3 3 7 5 3 . 8 0 5 4 7 8 0 . 0 0 2 9 7 5 4 0 . 1 8 5 9 6 9 0 . 6 3 5 8 6 2 0 . 6 2 9 2 5 3 0 . 6 3 2 5 5 7 0 . 0 0 4 6 7 3 5 0 . 232461 0 . 4 9 7 6 8 3 3 .5063.3 I 3 . 5 0 2 0 0 7 0 . 0 0 6 1 1 5 6 . 0 . 2 7 8 9 5 3 0 . 4 0 6 6 5 1 0 . 4 3 5 5 9 1 3 . 4 2 1 1 2 1 0 . 0 2 0 4 6 4 7 0 . 3 2 5 4 4 5 0 . 3 5 3 9 4 5 0 . 3 9 3 7 0 5 3 . 3 7 3 8 2 5 3 . 0 2 8 1 1 4 8 0 . 371 937 0 . 3 1 3 6 8 3 3 . 3 5 4 3 7 7 0 . 3 3 4 0 3 0 3 . 0 2 8 7 7 5 9 0 . 4 1 8 4 3 0 0 . 2 7 6 6 8 7 3 . 3 0 9 6 2 6 3 . 2 9 3 1 5 7 0 . 0 2 3 2 9 1 10 0 . 4 6 4 9 2 2 0 . 2 4 3 8 2 1 0 . 2 6 1 5 3 8 3 . 2 5 2 5 8 0 3 . 0 1 2 ^ 2 7 11 0 . 5 1 1 4 1 4 0 . 2 1 3 1 0 9 3 . 2 1 5 4 2 I 0 . 2 1 4 2 6 5 0 . 0 0 1 6 3 5 12 0 . 5 5 7 9 0 6 0 . 1 8 5 5 0 4 3 . 1 8 0 6 7 0 3 . 1 8 3 0 8 7 0 . 0 0 3 4 18 13 0 . 6 0 4 3 9 8 0 . 1 5 8 3 9 3 0 . 1 5 9 5 2 4 3 . 1 5 8 9 5 8 3 . 0 0 0 3 3 0 14 0 . 6 5 0 8 9 0 0 . 1 3 5 4 4 2 0 . 1 4 3 1 4 1 0 . 1 3 9 2 9 1 0 . 0 0 5 4 4 4 15 0 . 6 9 7 3 8 3 0 . 1 1 5 7 6 5 3 . 1 2 6 6 0 4 3 . 1 2 1 185 3 . 0 0 7 6 6 4 16 0 . 7 4 3 8 7 5 0 . 0 9 9 0 5 4 0 . 1 1 0 7 4 3 3 . 1 0 4 8 9 9 0 . 0 0 8 2 6 5 17 0 . 7 9 0 3 6 7 0 . 0 8 4 6 5 5 0 . 0 9 5 4 1 3 3 . 0 9 0 0 3 4 3 . 0 0 7 6 0 7 18 0 . 8 3 6 8 5 9 0 . 0 72313 0 . 0 8 3 6 0 1 0 . 0 7 7 9 5 7 0 . 0 0 7 9 H 1 19 0 . 8 8 3 3 5 1 0 . 0 6 1 5 1 5 3 . 0 7 4 2 8 1 3 . 0 6 7 8 9 8 0 . 0 0 9 0 2 7 20 0 . 9 2 9 8 4 4 0 . 0 5 4 1 1 3 0 . 0 6 7 9 6 5 0 . 0 6 1 0 3 9 0 . 0 0 9 7 9 5 21 0 . 9 7 6 3 3 6 0 . 0 4 9 2 9 8 0 . 0 6 2 3 1 7 0 . 0 5 5 8 0 8 0 . 0 0 9 2 0 5 22 1. 0 2 2 8 2 7 0 . 0 4 3 8 3 2 3 . 3 5 6 2 5 2 3 . 0 5 0 0 4 2 0 . 0 0 8 7 8 2 23 1 . 0 6 9 3 2 0 0 . 0 4 0 5 9 1 0 . 0 5 4 6 9 7 0 . 0 4 7 6 4 4 0 . 0 0 9 9 7 4 24 1 . 1 1 5 8 1 2 0 . 0 3 6 0 7 9 0 . 0 5 3 2 4 8 0 . 0 4 4 6 6 3 0 . 0 1 2 1 4 0 25 1 . 1 6 2 3 0 4 0 . 0 3 2 4 9 8 3 . 3 5 1 1 7 5 3 . 0 4 1 8 3 6 0 . 0 1 3 2 06 26 1 . 2 0 8 7 9 7 0 . 0 3 1 0 7 6 0 . 0 4 9 9 9 8 3 . 0 4 0 5 3 7 0 . 0 1 3 3 8 0 MTF at O d C . Exposure FREQUENCY I 0.046492 2 0.092984 3 0. 139477 4 0.185969 5 0.232461 6 0.278953 7 0.325445 8 0.371937 9 0.418430 10 0.464922 11 0.511414 12 0.557906 13 0.604398 14 0.650890 15 0.697383 16 0.743875 17 0.790367 18 0.836859 19 0.883351 20 0.929844 21 0.976336 22 1.022827 23 1.069320 24 I.115812 25 1. 162304 26 1 .208797 27 1.255288 28 1.301781 29 1 . 3482 72 30 I.394765 31 1. 44125 7 3 2 1 . 4 8 / i H 9 PULSE2 MTF I.000000 0.920133 0.788966 0.606371 0.498396 0.428170 0.380793 0.339577 0.295767 0.258842 0.229983 0.213858 0.205574 0.184153 0. 1560 70 0. 128300 0. 10 5240 0.090645 0.084804 0.086010 0.088897 0.080606 0.064258 0.048455 0.037892 0.033719 0.035563 0.041909 0.047246 0.049740 0.3 43636 0.035941 TABLE 7 time 17 seconds , medium l i g h t l e v e l . PULSE3 MTF 1.000000 0.92929? 0.798 03 6 3.637285 0.534735 0.469612 0.426055 0.381752 0.340250 0.307441 3.269887 0.231630 0.196702 3.16653 6 0.141547 0.12513 9 0.120962 0-114072 0.101031 3.086532 3.372205 0.063572 0.0 6095 7 3.063485 0.059748 0.054543 0.047213 0.04 3686 0.042316 ;> .0 44173 3 .354961 0.071410 AVE*AGE MTF 1 .000000 0.924712 0.793500 3.621828 3.516566 0.440891 3.403424 3 .360664 0.318009 0.283141 3 .249935 3.222744 0.201138 3.175345 3.148808 0.126719 3.113101 3.10235 9 0.09291 B 0.08 62 71 3.080551 0.072089 0.062608 3.054470 0.048820 0.044131 3.341388 3.042798 0.044781 0.046957 3.049299 0.053676 STAND.DEV. 0.0 3 .00S476 0.006413 0.021860 0.025695 0.029304 0.032005 0.02 98 2 2 3.031455 0.034365 0.0282 17 3-012557 0.0062 7 3 3.012457 0.0102S9 0.002235 0. 011 11 1 0.016565 3.011474 0.000369 0.011803 3.012044 0.002334 0.008507 0.015455 0.014724 0.008238 0.001257 3.003486 0.003937 0 . "J U b U U rl 3.025030 TABLE 8 MTF a t Q°C, Exposure time 35 seconds, medium l i g h t l e v e l . FREQUENCY PULSE2 MTF . P J L S E 3 MTF A V E * AGE MTF STAND. DEV, 1 0 .046492 1 .000000 I . 0 0 0 0 0 0 1 . 0 0 0 0 0 0 0 . 0 2 0 . 0 9 2 9 8 4 0 . 9 3 6 9 1 9 0 .935041 0 . 9 3 5 9 8 0 3 .001323 3 0 . 139477 0 . 8 2 0 5 4 3 0 . 8 0 6 0 4 4 0 . 8 1 3 2 93 0 . 0 1 0 2 5 3 4 0. 185969 0 . 6 5 6 9 4 9 3 . 6 4 6 5 8 0 3 . 6 5 1 7 6 4 0 . 0 0 7 3 3 2 5 0 .232461 0 .524772 0 . 5 3 4 7 1 0 3 . 5 2 9 7 4 1 0 . 0 0 7 0 2 7 6 0 .278953 0 . 4 3 9 1 1 3 0 . 4 6 3 1 7 6 0 . 4 5 1 1 4 4 0 . 0 1 7 0 1 5 7 0 .325445 0 .389172 0 . 4 1 6 4 1 7 3 . 4 0 2 7 9 5 0 . 0 1 9 2 6 5 8 0 . 3 7 1 9 3 7 0 . 3 4 9 5 6 7 0 . 3 6 8 8 6 0 3 . 3 5 9 2 1 3 0 . 0 1 3 6 4 3 9 0 . 4 1 8 4 3 0 0 . 3 0 8 8 4 5 3 . 3 2 2 0 7 8 3 .3154 SI 3 . 0 0 9 3 5 7 10 0 .464922 0 .270922 3 . 2 8 2 7 8 8 0 . 2 7 6 8 5 5 0 . 0 0 8 3 9 1 11 0 . 5 1 1 4 1 4 0 .236004 3 . 2 4 6 3 3 7 3 . 2 4 1 1 7 1 0 . 0 0 7 3 0 7 12 0 . 5 5 7 9 0 6 0 .204050 0 . 2 1 2 5 0 4 0 . 2 0 8 2 7 7 3 .005973 13 0 .604398 0 . 1 7 8 2 8 0 0 . 183337 0 . 1 8 0 8 0 9 0 . 0 0 3 5 7 6 14 0 .650890 0 . 1 5 4 6 2 9 3 . 1 5 H 3 1 8 3 . 1 5 6 4 7 3 0 . 0 0 2 6 0 8 15 0 .697383 0 . 132816 0 . 1 3 5 0 4 3 3 . 133930 0 . 0 0 1 5 7 5 16 0 .743875 0 . 1 1 4 0 9 3 0 . 1 1 8 0 7 7 0 . 1 1 6 0 8 5 0 . 0 0 2 8 1 7 17 0 .790367 0 . 0 9 5 9 9 5 0 . 1 1 1 8 8 0 3 . 103937 0 . 0 1 1 2 3 2 18 0 .836859 0 . 0 8 1 8 7 5 0 . 1 0 2 8 7 4 3 . 0 9 2 3 7 4 0 . 0 1 4 8 4 8 19 0 .883351 0 . 0 7 0 7 7 5 0 . 0 9 1 7 6 5 0 . 0 8 1 2 7 0 0 . 3 1 4 B 4 2 20 0 .929844 0 . 0 6 2 8 7 3 0 . 0 8 0 3 7 6 0 .071 625 0 . 0 1 2 3 7 6 21 0 .976336 0 .056817 3 . 367434 3 . 0 6 ? 125 0 . 0 0 7 5 0 8 22 1 .022827 0 .048478 0 .06052 3 3 . 0 5 4 5 0 0 3 . 0 0 3 5 1 7 23 1 .069320 0 .041021 0 . 0 5 8 8 5 6 0 . 0 4 9 9 3 9 0 .012611 24 1.115812 0 .034722 3 . 3 5 8 9 3 1 3 . 0 4 6 8 2 7 0 . 0 1 7 1 1 8 25 1 .162304 0 .030774 0 . 0 5 9 2 9 3 0 . 0 4 5 0 3 4 0 . 0 2 0 1 6 6 TABLE 9 MTF at 0 ° C , Exposure time 77 seconds , medium l i g h t l e v e l . FRFUUEMCY PUL SE 2 MTF P U L S E 3 MTF A V E R A G E MTF STAND.DEV. 1 0 . 0 4 6 4 9 2 1 . 0 0 0 0 0 0 I . 0 0 0 0 0 0 I . 0 0 0 0 0 0 0.0 2 0 . 0 9 2 9 8 4 0 . 9 0 2 3 6 1 0 . 8 9 9 5 5 5 3 . 9 0 0 9 5 8 0 . 0 0 1 9 8 4 3 0 . 1 3 9 4 7 7 0 . 7 3 2 8 1 2 0 . 7 0 5 3 8 7 3 . 7 1 9 1 0 0 0 . 0 1 9 3 9 3 4 0 . 1 8 5 9 6 9 0 . 5 0 1 0 2 0 0 . 4 6 0 9 7 8 0 . 4 8 0 9 9 9 3 . 0 2 8 3 1 4 5 0 . 2 3 2 4 6 1 0 . 3 3 8 8 3 4 3 . 3 1 9 9 4 5 0 . 3 2 9 3 8 9 0 . 0 1 3 3 5 6 6 0 . 2 7 8 9 5 3 0 . 2 4 5 9 7 8 3 . 2 4 9 1 6 5 3 . 2 4 7 5 7 2 0 . 0 0 2 2 5 3 7 0 . 3 2 5 4 4 5 0 . 2 0 1 7 5 0 0 . 2 1 2 0 6 4 0 . 2 0 6 9 0 7 3 . 0 0 7 2 9 3 8 0 . 3 7 1 9 3 7 0 . 1 7 1 5 0 7 0 . 1 8 0 75 0 0 . 1 7 6 1 2 9 0 . 0 0 6 5 3 6 9 0 . 4 1 8 4 3 0 0 . 1 4 5 0 6 1 3 . 1 4 7 6 8 7 3. 1 4 6 3 7 4 0 . 0 0 1 8 5 7 10 0 . 4 6 4 9 2 2 0 . 1 2 2 2 4 9 0 . 1 1 8 7 5 4 3. 1 2 0 5 0 1 0 . 0 0 2 4 7 1 11 0 . 5 1 1 4 1 4 0 . 1 0 3 5 5 3 0 . 0 9 5 3 5 8 0 . 0 9 9 4 5 5 0 . 0 0 5 7 9 5 12 0 . 5 5 7 9 0 6 0 . 0 8 5 9 8 4 0 . 0 7 6 0 0 0 0 . 0 8 0 9 9 2 0.00 7 0 6 0 13 0 . 6 0 4 3 9 8 0 . 0 6 9 9 0 4 0 . 0 6 5 6 0 6 3 . 0 6 7 7 5 5 0 . 0 0 3 0 3 9 14 0 . 6 5 0 8 9 0 0 . 0 5 7 4 1 5 0 . 0 5 9 1 1 8 0 . 0 5 8 2 6 6 3 . 0 0 1 2 0 4 15 0 . 6 9 7 3 8 3 0 . 0 4 5 4 9 5 3 . 0 5 4 4 7 6 0 . 0 4 9 9 8 5 0 . 0 0 6 3 51 1 6 0 . 7 4 3 8 7 5 0 . 0 4 0 5 2 1 3 - 0 5 3 0 9 4 3 . 0 4 6 8 0 8 0 . 0 0 8 8 9 1 17 0 . 7 9 0 3 6 7 0 . 0 3 4 5 4 5 0 . 0 5 2 5 3 1 0 . 0 4 3 5 3 8 3 . 0 1 2 7 18 18 0 . 8 3 6 B 5 9 0 . 0 3 2 3 2 5 0 . 0 4 5 6 7 7 0 . 0 3 9 0 0 1 0 . 0 0 9 4 4 I 19 0. 8 8 3 3 5 1 0 . 0 3 3 0 0 9 3 . 3 3 7 4 5 8 3 . 0 3 5 2 3 3 0 . 0 0 3 146 20 0 . 9 2 9 8 4 4 0 . 0 3 2 4 1 7 0 . 0 3 2 8 5 0 0 . 0 3 2 6 3 4 3 . 0 0 0 3 0 6 21 0 . 9 7 6 3 3 6 0 . 0 3 3 7 6 3 0 . 0 2 9 8 7 8 0 . 0 3 1 8 2 0 0 . 0 0 2 7 4 8 22 1 . 0 2 2 8 2 7 0 . 0 3 0 7 1 9 3 . 0 3 2 9 4 4 3 . 0 3 1 8 3 2 0 . 0 0 1 5 7 3 2 3 1 . 0 6 9 3 2 0 0 . 0 2 6 8 2 2 0 . 0 4 0 5 5 5 3 . 0 3 3 6 8 9 0 . 0 0 9 7 10 2 4 1 . 1 1 5 8 1 2 0 . 0 2 4 9 3 7 0 . 0 4 6 3 6 3 0 . 0 3 5 6 5 0 3 . 3 1 5 1 5 0 50 CONCLUSION It i s d i f f i c u l t to i s o l a t e the v a r i o u s mechanisms which c o n t r i b u t e to the MTF of the i s o c o n d e t e c t o r . But at s h o r t exposure t imes the f i n i t e width of the r e a d i n g beam ( 220 microns on the photocathode) a c t s as an ana log f i l t e r wi th a d e f i n i t e h igh f requency c u t - o f f . T h i s p revents a l i a s i n g or u n d e r - s a m p l i n g p r o v i d e d tha t the scan s e p a r a t i o n i s l e s s than the beam w i d t h . By comparing F i g u r e 7 and F i g u r e 13a, we see tha t the maximum MTF se t by the assumpt ions of Kr i t tman (1962) r e g a r d i n g the c h a r g e - t o - p o t e n t i a l t r a n s f e r at the t a r g e t i s exceeded i n the P850 i s o c o n . I t i s c o n c l u d e d , t h e r e f o r e , tha t the Kr i t tman formula does not apply i n our case because of the very l a r g e t a r g e t m e s h - t o - t a r g e t s p a c i n g and t h i n t a r g e t . An examinat ion of F i g u r e s 13 and 14 w i l l r e v e a l the e f f e c t s of charge spread at the t a r g e t on r e s o l u t i o n . For l o n g e r exposure t imes i t i s obv ious tha t a low t a r g e t temperature i s r e q u i r e d . S e v e r a l t h i n g s can be suggested f o r improvement of r e s o l u t i o n i n the i s o c o n s y s t e m . The most obv ious i s a l o w e r i n g of t a r g e t t e m p e r a t u r e . However, because of the grea t d i f f i c u l t y i n u n i f o r m l y r e f r i g e r a t i n g the very l a r g e 51 t u b e , and the danger of thermal s t r e s s e s o c c u r r i n g i f un i fo rm c o o l i n g i s not a c h i e v e d , lower t a r g e t temperatures cannot be o b t a i n e d wi thout g rea t d i f f i c u l t y and some r i s k . Some improvement i n r e s o l u t i o n c o u l d be had by s c a n n i n g a long the s p e c t r a r a t h e r than normal to the s p e c t r a . Because of the s e l f - " s h a r p e n i n g " e f f e c t d i s c u s s e d by C H . Schade, S r . (1967) there would be an i n c r e a s e i n r e s o l u t i o n a long the l i n e scan d i r e c t i o n . However because o f the tremendous data r a t e r e q u i r e d by scann ing i n t h i s d i r e c t i o n (sample r a t e of at l e a s t 10 samples per m i c r o -second) t h i s method i s at p r e s e n t c o n s i d e r e d u n f e a s i b l e . The i s o c o n system as i t now s tands has been used f o r over one y e a r . It has proved to be a u s e f u l and v e r s a t i l e t o o l f o r the o b s e r v a t i o n o f a s t r o n o m i c a l s p e c t r a . 52 BIBLIOGRAPHY K r i t t m a n , I .M . , R e s o l u t i o n of E l e c t r o s t a t i c Storage T a r g e t s , IEEE T r a n s a c t i o n s on E l e c t r o n D e v i c e s , V o l . ED-10 , p. 404, The I n s t i t u t e of E l e c t r i c a l and E l e c t r o n i c Eng ineers I n c . , New York , 1963. L a t h i , B . P . , S i g n a l s . Systems and Communicat ion, John Wi ley and Sons , New York , 1965. r Mauser, D . P . , The Image Isocon—A Low-L igh t L e v e l T e l e v i s i o n Tube, IEEE T r a n s a c t i o n s on B r o a d c a s t i n g , V o l . BC-15, No. 2, p. 39, The I n s t i t u t e of E l e c t r i c a l and E l e c t r o n i c E n g i n e e r s I n c . , New York , 1969. N e l s o n , P . D . , Advances i n E l e c t r o n i c s and E l e c t r o n P h y s i c s , e d . by J . D . McGee, D.McMullen and E . Kaham, V o l . 28A, p. 209, Academic P r e s s , London, 1969. Schade , O . H . , The R e s o l v i n g - P o w e r F u n c t i o n gnd Quantum P r o c e s s e s of T e l e v i s i o n Cameras, RCA Review, V o l . 28, p. 460, RCA L a b o r a t o r i e s , P r i n c e t o n , New J e r s e y , 1967. Walker , G . A . H . , Auman, J . R . , B u c h h o l z , V . L . , G o l d b e r g , B . A . , Gower, A . C , Isherwood, B . C . , K n i g h t , R . , W r i g h t , D . , A p p l i c a t i o n o f an Image Isocon and Computer to D i r e c t D i g i t i z a t i o n o f A s t r o n o m i c a l S p e c t r a , Advances i n E l e c t r o n i c s and E l e c t r o n P h y s i c s , i n p r i n t , Academic P r e s s , London. 53 APPENDIX A SYSTEM SCHEMATICS Schemat ic Page Board I, V ideo F o l l o w e r 54 Isocon Rear Socket I n t e r c o n n e c t i o n 55 Board J 56 Board H 57 V ideo A m p l i f i e r 58 Focus C o i l C u r r e n t R e g u l a t o r 59 Master C o n t r o l U n i t (In Pocket ) Isocon Camera Main Frame (In Pocket ) L i n e Scan Un i t (In Pocket ) o 54 VIDEO FOLLOWER S K B C • 1400 V ISOCON REAR SOCKET INTERCONNECTION BOARD J LINEARITY 5 0 0 1 L - O : _ O . Qu BOARD H • u v Q CD VIDEO AMPLIFIER F O C U S C O I L C U R R E N T R E G U L A T O R 60 APPENDIX B COMPUTER PROGRAMS 61 N( 1) DIMENSION AM T F M ( 4 5 3 ) DIMENSION D(451) , 3 S 3 E C (2000) , AS? 1 ( 2 0 0 0 ) , AMTF( 4 5 3 ) , F * EQ ( 4 5 0 ) RE AL STARl 4000) , i> [ 400 0) , XP( 4 0 0 3 ) S IMPLEX TRAN< 2033 ) , W O R M 2 0 0 0 ) READ ( 5 , 1 1 0 0 ) L 3 E 5 , L N u V W I D T H 1 , SE P , WI DTH2 , HL , HH , SR 1100 FDRMAT ( 2 I 5 , 5 F 6 . 3 ) L I = I F I X ( W I D T H 1 * S R * 1 3 . 0 + 1 . 5 ) L2=I= IX( ( tl I DT HI +SE 3 ) *=S R * 10 . 0+ I . 5 ) t 3 = I c I X ( ( W I D T H l + S E ' + W I D T H 2 ) * S R * 1 0 . 0 + 1 . 5 ) E Q U I V A L E N C E ( S T A R . T R A N ) t H \ ' 0 0 = L N O / 2+1 L ^ 3 = 1 0 * L N 0 L H N D = L N 0 / 2 + l 3 0 29 J = i , L l 29 STAR(J )=HL 3 3 501 J = L 1 . U 2 5 0 1 S T A R ( J ) = 0 . 0 3 3 5 0 3 J = L 2 , L 3 5 0 3 S T A R ( J ) = r H 3 0 5 0 5 J = L 3 , L N 0 505 S T A R ( J ) = 0 . 0 C * * N 3 R M A L I Z I N G TO 103 AT MAX 17 X X = S T A R ( l ) M ( 1 ) = L N O 3 3 1 5 J = 1 , L N 0 IF ( S T A R ( J ) . G E . X O 5 0 T O 15 XX = S T A R . ( J ) 15 : D N T I N U E 3 0 1 6 J = l , L N O 16 S T A R l J ) = S T A R ( J ) - < X XX = S T A R U ) 3 3 12 J = 1 , L N 0 IF ( S T A R ( J ) . L E . X O 3 0 T O 12 XX = S T A R ( J ) 1 2 : 0 N T I N U 6 FAC = 1 0 0 . 0 / XX 3D 1 3 J = i , L N 0 S T A R ( J ) = FAZ * S T A U J ) 1 3 C O N T I N U E C * * U N F I L T E R E D S C A ^ O U T P U T W R I T E ( 6 , 1 0 8 ) 10B F D R M A T ( • O S I G ^ A L M W R I T E ( 6 , 1 0 0 ) ( S T A R ( J ) , J = 1,L^1D) 1 0 0 F D R M A T ( • • , 2 0 F 6 . 2 ) 2 2 W R I T E ( 6 , 1 0 1 ) 1 0 1 F D R M A T I • OAM PL I TUD E S P E C T R J * 1 ) C * * T R A N S F O R M I N 5 : A L L F O U R T ( S T A R , ^ , 1 , - 1 , 0 , W O R K , 2 0 0 0 ) 3 3 2 0 J = 1 , L F N D P S P E C ( J ) = S Q R T ( R E A L ( T \ A N ( J ) * C 0 ^ J G ( T R A N U ) ) ) ) 2 0 : 0 N T I N U E W R I T E ( 6 , 1 0 6 ) ( P S ' E C t J ) , J = 1 , L H N 3 ) 1 0 6 F D R M A T ( » • , 5 F 1 3 . 5 ) W R I T E ( 8 ) ( P S P E 3 ( J ) , J = l , L H N 0 0 ) 9999 STOP END C * * 4 CONTAINS AMP SPEC DF INPJT P J L S E S C * * 5 CDNTAIN'S L B E G , L ^ D , S * ( 2 I 5 , 1 F 6 . 3 ) C * * 7 CONTAINS NWIND M D . OF POINTS IN WINDOWU5)) C AND WIND (WINDOW VALUES ( 8 F 1 0 . 5 ) ) c**a CONTAINS OJTPUT J U L S E S IN TE J E R. N i l ) 3 I ME NSI ON AMTFN( 453 ), K IND150) 3 I MENS I ON D( 451) , ? S ? E C ( 2 000) , A S? 1 (2 OO 0 ). A MT F ( 4 53 ), F I E3( 450) REAL STAR(4 0 0 0 ) , 40 0 0 ) , X P ( 4 0 3 3 ) COMPLEX TRAN( 2033 ),WO*K( 2000) READ ( 8, 1000) ( 3 ( L ) , L = 1 , 4 5 1 ) 1C00 FDR MAT ( 5 0 F 5 . 0 ) READ ( 5 , 1 1 0 0 ) L 3 E G» LNO, SR 1100 FORMAT ( 2 I 5 , 1 F 6 . 3 ) READ ( 7 , 5 ) NrfIND READ 1 7,503) ( W H 3 { J ) • J = 1, HA I ) 5 FORMAT (15) 503 FDRMAT ( 8 F 1 0 . 5 ) ^HWIND=NWIND/2 DD 500 J = i , L N O S T A R ( J ) = C (LB EG) LBEG = LBEG«-1 500 CONTINUE N ( 1 ) = L N 0 LHND=LN0/2 f1 L^OO=LNO LHNOO=LHNO EQUIVALENCE ( S T A R , A N ) L=0 M=0 : A L L PLOTS C**NDR,MALI ZI NS TO 103 AT MAX 17 XX=STA!U 1) >I(1)=LN0 DD 15 J = 1 , L N 0 IF { S T A % ( J ) . G E . X < ) SO TO 15 XX = STA iU J ) 15 CONTINUE DO 16 J = 1 . L N 0 16 S T A R ( J ) = S T A R ( J )-XX XX = S T A R ( l ) D3 12 J = i , L N O IF ( S T A * ( J ) . L E . X < ) 30 TO 12 XX = S T A R ( J ) 12 CONTINUE FAC = 1 0 0 . 0 / XX DD 13 J = i , L N O S T A R ( J ) = FA3 * S T A U J ) 13 CONTINUE C * * U N F I L T E * E D SCAN OUTPUT WRITE ( 6 , 1 0 8 ) 108 FDRMAT C O S I G ^ A L M WRITE ( 6 , 1 0 0 ) ( S T A U J ) , J = l , L S 3 ) 100 FDRMAT ( » « , 2 X , 2 D F 6 . 2 ) DD 21 J = 1 , LM3 X = > ( J ) = ( . 1 0 * J ) - . l 3 21 CONTINUE DD 14 J = 1 , LM3 Y ? ( J ) = S T A R ( J ) / 2 0 . 0 I- 2 . 0 1 4 CONTINUE 63 CALL L INE ( X P . Y P , L N O , I ) A = IF IX ( XP(LNO) +2.0 J CALL PLOT ( A , 0 . 3 , - 3 ) C * * T R A N S F D * M I N J CALL FQU^T (STAR,N,1, -1,0,WORK,2000) 33 20 J = 1, LHN3 PSPEC( J ) = SQRT( REALI T* AN( J )*CON J G ( T R A N ( J ) ) ) ) 20 CONTINUE C* *AMPL ITUDE SPECTRUM 3UTPUT. 22 WRITE ( 6 , 101) 101 FDRMAT ( •OAMPL ITUDE SPECTRJM* ) WRITE (6 , 1 0 6 ) ( ? S 5 E C ( J ) , J = 1 , L H N 3 ) 106 FDRMAT (• • , 5 F 1 3 . 5 ) 3D 2 5 J= 1,LHN0 X 3 ( J )= ( . l * J ) - . 1 Y ? ( J ) = ( P S P E C l J ) / ' S ? E C ( 1 ) ) * 1 3 . 0 IF ( Y P ( J ) . G T . 1 0 . 3 ) r P ( J ) = 10.D 25 CONTINUE A=IF I X U P ( L H N D D ) +2.0) CALL L INE ( X P , Y P , L H N O O , 1 ) C A L L PLOT ( A , 0 . 3 , - 3 ) L = L + i IF ( L . E 3 . 2 . 0 R . L . E D . 4 ) 30 TQ 704 C**SM03THIN3 3D 31 J=l,NHWIND 31 STAR(J )=PSPEC(NHWIND+2-J ) DD 701 J=1 ,LHN0 701 STAR(NHWIND+J)=PSP=C(J) 3D 702 J = l ,LHNO P S P E C ( J ) = 0 . 0 DD 703 NN=1,NWIND 703 P S P E C ( J ) = P S P E C ( J ) + S T A R I J - U N N ) *W IND ( NN) 702 CDNTINUE G3 TO 22 70 4 CONTINUE M = H+1 IF ( M . N E . l ) GO TD 505 C**READIN3 AMP SPEC DF INPUT P J L S E 9 DD 2 8 J =1,LH*10 28 A S P K J ) = P S P E C ( J ) READ (4) ( PSPEC< J ) , J = 1,LHN0) GO TO 2-2 5 05 CDNTINUE ' C**ND RM AL I ZE AND OUTPUT MTF CALL AXIS ( 0 . 0 , D . O , •CYC /MM 1 , - 6 , 1 0 . 0 , 0 . 0 , 0 . 0 , 3 . 2 ) C A L L AXIS ( 0 . 0 , 3 . 0 , • M T F ' , 3 , 1 0 . 3 , 9 3 . 0 , 0 . 0 , . 1 2 5 1 WRITE (6,801) 801 FDRMAT ( » 0 FREQUENCY NDR MALI I ED MTF»] 33 601 J=2 ,LHN03 AMTF ( J ) = A S P K J ) / ' S ^ E C U ) F R E D { J ) = F L O A T ( J - l ) * S * / L N O O AMTF N ( J ) = AMT F ( J ) / A M T F ( 2 ) WRITE (6, 1200) J , F * E O ( J ) , A M T F M ( J ) 1200 FDRMAT ( I 5 ,2F20 . 6 ) WRITE (3 ) FREQ( J) , A M T F N U ) 601 CONTINUE DD 602 J=2,LHND3 IF ( F R E Q ( J ) . G T . 2 . 0 ) 30 TO 603 IF ( A M T F N ( J ) . G T . l . l 875 ) AMT FN ( J) =1 .25 X 3 ( J ) = F* EQ(J)*5.D Y?(J)=AMTFNfJ}*3.0 CALL SYMBOL ( XP( J ) , i? ( J ) , . 01 , 3,D .0 , -1 ) 602 CONTINUE 603 CALL PLOTNO 9999 STOP E^O 65 D I MENS I CN AMTFH 233 ), AMTF2( 200) , PRE 3 (200) : A L L PLOTS L=0 LHN0=65 WRITE (6.14) 14 FDRMAT ( • 1 » / / / / / / / / / / 15X, •FREQUENCY», 7X» • PJ_S - F « , 6 X , 'AVERAGE M T= • , SX, • S T i \ 'D . DE V . •) : A L L AXIS ( 0 . 0 , 3 . 3 , » M T F • , 3 , 1 0 . 3 , 9 3 . 0 , 0 . 0 , . 1 ) SALL AXIS (0. 0 , 3 . 3 , 'CYC/MM* , - 6 , 13 . 0 , 0 . 0 , 0 . 0 , 0 3D 11 J=l ,LHNO READ (3) FREQ< J) , AMTFIIJ ) READ (4) FREQl* J) , AMTF2 t J ) AV=( AMTF l ( J ) « - A « T F 2 ( J ) ) / 2 . 0 SD = ( ( AV- AMT f 1 ( J) )**2+( AV-A1TF2I J ) ) * *2 ) * *0 . 5 WRITE (5,12) J , F R E 3 1 J ) , A M T F 1 ( J) , AMTF2 (J ) , W , S 12 FDRMAT ( I 8 , 5 F 1 7 . 6 ) AV=10.0*AV SD=10.0*SD F R E 3 ( J ) = F R E Q ( J ) * 5 . 3 : = S D / A V IF ( C . 3 T . 0 . 2 5 ) L=L+t IF ( L . E Q . 3 ) GO TD 13 IF (FREQ( J ). GT. 13.3 ) 30 TO 13 CALL SYMBOL ( F R E 3 ( J > , A V , S D , 1 3 , 3 . 3 , - l ) 11 CONTINUE 13 WRITE (6,15) 15 FDRMAT ( » 1 » ) 2ALL PLOTNO STOP END 

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