Integrated circuits take the cams out of cameras

Microelectm~nics and Reli~bility, Vol.18, pp. 35-47. Pergamon Press, 1978. Printed in Great Britain

INTEGRATED CIRCUITS TAKE THE CAMS OUT OF CAMERAS David Anderson Siemens A.G., WIS TE 121, Balanstrasse 73,8000 Milnchen 80, West Germany

Over the past five years the camera industry, once the exclusive domain of precision mechanics, has undergone a quiet revolution. From small beginnings with a few passive components and the odd transistor, the trend to electronics progressed rapidly to include standard ICs and, with the boom in the pocket-camera industry, new concepts and specialised ICs for cameras were developed. These techniques are today being applied to more sophisticated cameras where the complexity and special requirements of the camera sub-system are proving a test for the very latest in IC technology. Considerable experience in this field has been gathered in the development laboratories of Siemens in Munich and this paper explains the problems encountered, reviews the capabilities of present integrated circuits, and looks briefly into the future. Introduction The first selenium photo-sensors were introduced into cameras over 40 years ago but it was not until 1957 before more sensitive, battery-powered cadmium sulphide photo-sensors began to be used in camera exposure meters. It was, however, the introduction of "electronic" shutters around 1965 which marked the take-off point of a quiet revolution toward electronification which has not yet reached its climax and may culminate with production of a compact, totally electronic camera, and the disappearance of the mechanical marvels as we know them today. Early Circuit Techniques Up until recently, the cadmium sulphide photoconductive cell has been the most widely used type of light sensor. Early circuits made use of a bridge connection to balance a meter when the aperture was correctly set. For this fixed-point matching system the photo-cell was mounted behind the aperture and filmspeed compensation was achieved by a step wedge or by means of a variable resistor in one arm of the bridge. In automatic cameras discrete transistors were used to trigger a miniature relay after a delay time which was determined by integrating the light-dependent current from a photo-cell on a capacitor until a preset trigger level was reached. The introduction of bipolar operational amplifiers not only offered the camera manufacturer noteable space advantages but also, by virtue of their smaller input currents, increased measurement sensitivity making longer automatic exposure times possible. Some operational amplifiers such as the TCA 335, are capable of driving a relay directly without an additional external transistor. In such circuits it is usually necessary to provide a small amount of hysteresis as shown in fig. I to prevent possible oscillation of the relay and the direct use of an integrated schmitt-trigger, (figs. I and 2), was an obvious transition. 35

36

D. Anderson

f c r

R,

:

_

2"

L

_

S 1=shutter release button Fig.

i.

Simple

circuits

for

automatic

exposure-time

control

o2

~4 1"13 D1 [D2

~-~ Fig.

2.

Circuit

of

Schmitt

Trigger

IC:TCA345

The rapid g r o w t h of the p o c k e t - c a m e r a i n d u s t r y in the mid 1970~ b r o u g h t with it a g r e a t e r d e m a n d for f o o l - p r o o f cameras with m o r e a u t o m a t i c features. The IC shown in fig. 3 provides, in a d d i t i o n to a u t o m a t i c time exposure, a light check and a b a t t e r y c h e c k facility. A f u r t h e r e v o l u t i o n is d e p i c t e d by the IC shown in fig. 4, w h i c h m a y be used to c o m b i n e the a d v a n t a g e s both of a f i x e d - p o i n t m a t c h i n g s y s t e m for a p e r t u r e a d j u s t m e n t and fully a u t o m a t i c e x p o s u r e time. In its b a si c form the IC c o n t r o l s a r e l a y d u r i n g the l i g h t - c h e c k m o d e to select the smaller of two a p e r t u r e s w h e n light levels p e r m i t and, in addition, a r e d / g r e e n i n d i c a t i o n w a r n s the user of long e x p o s u r e times and the need to use a tripod. If a f u r t h e r LED is c o n n e c t e d to the o u t p u t n o r m a l l y u s e d for the a p e r t u r e relay the IC m a y be e m p l o y e d in c a m e r a s w h e r e the p h o t o - c e l l is m o u n t e d b e h i n d the lens to p r o v i d e the user w i t h a r e d / g r e e n / o r a n g e i n d i c a t i o n as to w h e t h e r the ideal a p e r t u r e has been m a n u a l l y selected. In e i t h e r case the i n f o r m a t i o n is stored in the IC at the m o m e n t of s h u t t e r - r e l e a s e and e x p o s u r e time is fully automatic.

~3

ICs take the Cams out of Cameras

$1

iL

I

$2'

37

relay 171 4

s

LED

3S258' CI

"z"

2

7

1

8

RTr ~

S 1-power on

S 2-te: d/shutter release S 3-fla

S 4--fil, advance control Fig.

3

Circuit diagram light-check and

for automatic battery-check

camera with facilities

Further Applications of Camera ICs Although designed specifically for operation inside cameras, most ICs of this type may be used in a variety of associated applications, including light-to-frequency converters, hand-held light meters, automatic exposure systems for photographic enlargers, light-sensitive switches and, in conjunction with the appropriate sensors and filters, for the automatic processing of colour films. The scope of this presentation does not enable in-depth descussion of these applications.

"Sll

'

4

S2

shutter i relay r"~'l

I' 10~ C~o,tro~ !

~OV relayl--r-L" 'J' ;~dII f.no.I

_L_C,

_L.

..T. _T.

T

l l

,-

,,,,

;

OV

I

"

I

9 OV Fig. 4.

Block diagram of a pocket-camera IC with automatic exposure time and f-number selection

Test and Manufacture of Camera ICs Bipolar camera its may be manufactured and tested using very similar processes to those required for other bipolar linear

I

38

D. Anderson

circuits. A l t h o u g h the t e s t i n g of s u c h ICs on the s l i c e and in t h e p a c k a g e is f u l l y a u t o m a t i c , a probl-em a r i s e s w i t h the c a m e r a m a n u f a c t u r e r w h o is o f t e n n o t e q u i p p e d w i t h e x p e n s i v e t e s t and electrical diagnosis equipment. H o w e v e r , it is p o s s i b l e to t<:s< a n u m b e r of c i r c u i t f u n c t i o n s w i t h a v e r y s i m p l e t e s t c i r c u i t . Fig. 5 s h o w s two c u r v e s o b t a i n e d by c o n n e c t i n g an a u t o m a t i c c a m e r a IC to a t r a n s i s t o r c u r v e - t r a c e r . C u r r e n t , v o l t a g e and s w i t c h i n g l e v e l s m a y be c h e c k e d and, by c o n n e c t i n g a high--v~]~, r e s i s t o r in t h e b a s e c o n n e c t i o n line, the e f f e c t of e x c e s s i v e i n p u t c u < r e n t m a y be o b s e r v e d .

Light-Check Mode

Exposure Mode

~

Rt

E

J

c

1 mA/div. A

f

Ec

m/~/div.

G H~'

,J],,~ F E ---~

1 Volt/div.

A --=,- battery-check voltage B - - ~ LED trigger level BC --=" LED current Fig,

5.

Simple using

--~

E --=~ IC current consumption EF - - ~ built-in hysteresis test method a transistor

for a camera curve-tracer

IC

S p a c e is at a p r e m i u m in c a m e r a s and in g e n e r a l s p e c i a l l y designc~:] b a s e - b o a r d s a r e s c a t t e r e d a r o u n d the s p a c e s i n s i d e the c a m e r a , o f t e n c o n n e c t e d to o n e a n o t h e r by f l e x i b l e p r i n t e d c i r c u i t b o a r d s . E v e n t h e s t a n d a r d d u a l - i n - l i n e p a c k a g e p r o v e s to be u n n e c e s s a r : i ] v bulky and for this reason the micropacYage s h o w n in fig. 6, is i d e a l for u s e in c a m e r a s .

Photo-Sensors

and Circuit

Input

Configurations

In e a r l y e l e c t r o n i c e x p o s u r e m e t e r s s e l e n i u m p h o t o - s e n s o r s found widespread application. T h e o p t i c a l r e s p o n s e of s e l e n i u m c o r r e s p o n d s c l o s e l y to t h a t of the h u m a n eye a n d the o u t p u t is s u f f i c i e n t to d r i v e a m e t e r w i t h o u t a b a t t e r y . The n e e d for greater photo-sensitivity at low c o s t a n d t h e a v a i l a b i l i t y of miniature button-cells led to the w i d e s p r e a d u s e of c a d m i u m sulphide photo-sensitive r e s i s t o r s . The o p t i c a l r e s p o n s e of CdS (fig. 7), a l t h o u g h n o t i d e n t i c a l to t h a t of the e y e p r o v e s to be acceptable and photo-sensitivity m a y e x t e n d d o w n to less t h a n I lux. H o w e v e r , some c h a r a c t e r i s t i c s of C d S p h o t o - s e n s o r s are less t h a n i d e a l as s h o w n in fig. 8. T h e v a r i a t i o n of r e s i s t a n c e w i t h l i g h t is n o t e n t i r e l y l i n e a r , c h a n g e s w i t h t e m p e r a t u r e ( e s p e c i a l l y at low l i g h t i n t e n s i t y ) and, w o r s t of all, it e x h i b i t s a s t r o n g m e m o r y e f f e c t w h i c h is m o s t p r o n o u n c e d at low l i g h t intensities. Silicon exhibit

1 Volt/div.

photo-sensors, on the o t h e r hand, are fast, v e r y l i n e a r , c l o s e l y p r e d i c t a b l e t e m p e r a t u r e d r i f t s , and m a y be

ICs take the Cams out of Cameras

39

Max. Nr. of pins-20 Max, size of chip-3.2X 1.9 mm Overall dimensions--8.0 X 4.2 X0,6 mm Fig.

6.

A typical

micropackage--format

8 nun lilm

% 100 Relative Sensitivity

t

90 80

I

/

\

-oaA,sp

,4,

human eye-

\,

70

f/

/

60 5040

p,

.,;r

10 0

4OO

50O

\

t1, \ \

/

3O 20

700

600

800 ~ w

h_ ~Iml-Vl

All "

~la I

,Si

it.

., ~ I ~ F T T

kmA w•

.

900

1000 nm

Wavelength ~,

II " i

.I

violet blue green |orange red yellow Fig.

7.

Relative

spectral

sensitivities

of various

photo-detectors

s e n s i t i v e to light i n t e n s i t i e s less than 100 mlx. The o p t i c a l r e s p o n s e of s i l i c o n is not ideal, however, w i t h a strong l e a n i n g to the i n f r a - r e d f r e q u e n c i e s so that m o s t c a m e r a s fitted w i t h Si p h o t o - s e n s o r s m a k e use of o p t i c a l filters w h i c h can reduce the u s a b l e s e n s i t i v i t y by a factor of 4. Silicon p h o t o - d i o d e s n e v e r t h e l e s s , offer the n o t a b l e a d v a n t a g e that they m a y be i n t e g r a t e d on the same chip as a b i p o l a r amplifier, thus extending the useful range of s e n s i t i v i t y and freeing the c a m e r a m a n u f a c t u r e r from the p r o b l e m of a n a l y s i n g c u r r e n t s in the n a n o a m p range. One such device, the TFA 1001W a m p l i f i e d photos e n s o ~ is c o m p a r e d in fig. 9 to a n o r m a l silicon p h o t o - d i o d e .

40

D. Anderson

Light resistance as a function of illuminance RH=f (Ev) (spread)

Ri 7106 1~

Light resistance as a function

RHT=f (Tamb) of temperature R---~-~5o

~~k

3 RH25°I ] & 2'RHT

65%

10:, i : 103~risetime

lilx

104

Rise and fall time of the photocurrent to of the final value as a function of illuminance t - f (Ev)

x RP

103 0 100 101 102 1031x--50 --~E v Fig.

8.

0

100°C 100

50

--~Tam b

Characteristies

of

a typical

Relative spectral sensitivity Sr,l=f (~,)

100 %

,o.///

TFA~ ~B

101 10° 10-1 . ~

2O

TFA1001

o

I p 25°

PX 63

i I

I

ip

i~=f (Tamb)

TFA1001 102 1.2 mA 101 Ip

BPX 63

102

l-l/

photo-resistor

Photocurrent

max. sensitivit' of eye

101 Ix 102 ----z,-Ev

100 ~0.8 10-1 0.6 BPX63andTFA1001 10-2 0.4 10-3 0.2

-20 0 20 40 °C 80 400 600 800 nm 1200 10-1100 101 10210Zlx --i,~,% Tamb -----~Ev 0,0050,05 0,5 5 mW/cm 2 !

a

I

I

a

--"-~'Ee Fig.

9.

Comparison

of p h o t o - d i o d e

BPX63

and photo-amplifier

TFA

In its b a s i c f o r m the d e v i c e ]s a l i g h t - t o - c u r r e n t converter w i t h a l i n e a r r a n g e e x t e n d i n g o v e r f i v e d e c a d e s of l i g h t i n t e n s i t y variation. A c o n s i d e r a t i o n of v a r i o u s i n p u t c i r c u i t c o n f i g u r a t i o n s is d e p i c t e d in fig. 10. In t h e s i m p l e s t of c i r c u i t c o n n e c t i o n s , n u m b e r I, a light-dependent c u r r e n t is i n t e g r a t e d on a c a p a c i t o r to a p r e s e t t r i g g e r level, Vtr, to p r o v i d e a n e x p o s u r e t i m e te g i v e n by.

iOOlW

ICs take the Cams out of Cameras

t i

~

"

I

41

RF

0

,lXl or,,

Fig.

i0.

-

Various p h o t o - s e n s i t i v e

t e = -RfC Ln

l-

,

input c o n f i g u r a t i o n s

Vtrl

Input c i r c u i t number 2 c o m b i n e s the basic e x p o s u r e time delay c i r c u i t w i t h a simple l i g h t - s e n s i t i v e p o t e n t i a l d i v i d e r to trip a s c h m i t t - t r i g g e r in the case of low light intensity. The photor e s i s t o r is t i m e - s h a r e d b e t w e e n both functions by a l t e r n a t e l y s h o r t i n g the other two components. In circuit number 3 a silicon p h o t o - d i o d e d i s c h a r g e s a small c a p a c i t o r at a rate p r o p o r t i o n a l to the light intensity. A j u n c t i o n FET is e m p l o y e d as a sourcef o l l o w e r to prevent loading of the input by the f o l l o w i n g (bipolar) circuit. Input c o n f i g u r a t i o n n u m b e r 4 d e m o n s t r a t e s the s i m p l i c i t y of a p p l i c a t i o n of the TFA I001W a m p l i f i e d photo-sensor. In both circuits, 3 and 4, p h o t o - c u r r e n t is largely i n d e p e n d e n t of the v o l t a g e across the d e v i c e and the e x p o s u r e time, t e, is g i v e n by te = C[Vtr - Vo] if

if

=

photo-current

Vtr

=

trigger v o l t a g e

Vo

=

starting v o l t a g e

It Will be o b v i o u s that e a c h of these input circuits may be u s e d as the basis of l i g h t - t o - f r e q u e n c y c o n v e r t e r s when c o n n e c t e d to a m u l t i v i b r a t o r - t y p e circuit. In general, however, for a p p l i c a t i o n s where a v e r y large dynamic range is required, a current output is easier to a c c u r a t e l y e v a l u a t e than a f r e q u e n c y output.

M p r e c S g p h i s t i c a t e d Camera ICs In a p p l y i n g the above c i r c u i t t e c h n i q u e s to a u t o m a t i c c a m e r a s it is n e c e s s a r y to u n d e r s t a n d the r e l a t i o n s h i p of film-speed, aperture and e x p Q s u r e time, t e, at a given light intensity. This r e l a t i o n s h i p is shown g r a p h i c a l l y in fig. 11, in terms of socalled "light values". Good a u t o m a t i c cameras have an o p e r a t i n g range of over 2 'g ~ t y p i c a l l y from light value 1 to 18. It will be obvious that a dynamic range of this m a g n i t u d e poses a severe p r o b l e m for the e l e c t r o n i c control circuit. In the s o l u t i o n of this p r o b l e m three d i f f e r e n t a p p r o a c h e s are possible:

42

D. Anderson

°DIN "~' 42

39 36 33 30

Exposure time 27 24 21 18 15 12 9 6 A ' 1/2 1/4 1/8

l

1/15 1/30 1/60 1/125 1/250 1/500 1/1000

Ape

t

I

-6-5-4-3-2-1 Fig.

ii.

0 1 2 2; 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 , z,- Light value Relationship

a)

Program

b)

Logarithmic

c)

Digital

- Controlled

between

film speed/f-number/exposure

time

Shutters

Compression

Techniques

Fig. 12 s h o w s the p r i n c i p l e of a p r o g r a m m e d s h u t t e r as u s e d in a n u m b e r of m i d d l e r a n g e a u t o m a t i c c a m e r a s . In p r i n c i p l e , the s y s t e m s e l e c t s the s m a l l e s t a p e r t u r e and s h o r t e s t t i m e p o s s i b l e in a c c o r d a n c e w i t h l i g h t c o n d i t i o n s b u t b a s e d o n a "pre-program~rned :' relationship. Thus, long exposure times with small apertures (or v i c e v e r s a ) a r e i m p o s s i b l e , b u t a l a r g e r a n g e is a c h i e v e d at a modest outlay.

Bright

Dark f 2.8

k _ _ radiant

radiant

"°xt

""xt

/ ~

/

f221~0 ]f22 0 I

~

20ms

0 !<<

.,'I i

mechanical and electrical time periods 12.

I

of

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teff=l/30sl

I

II,I L

1{)

2()

3'0

4()

5'0

mechanical time period electrical time period

Principle

!'

IL

•

f22 j~"

te.=l/100s

Fig.

'7i

closing

a programmed-shutter

6'0 ms I --'~t )t I .I

,I

.,

ICs take the Cams out of Cameras

43

L o g a r i t h m i c c o m p r e s s i o n allows a p h o t o - c u r r e n t w h i c h may vary over five decades to be r e p r e s e n t e d on a small v o l t a g e scale. The voltage across a diode varies a c c o r d i n g to the w e l l - k n o w n equation: V d ....

Ln

is

- I

i#

= idealised saturation current

k

=

Boltzman§ c o n s t a n t

q

= charge on e l e c t r o n

If the diode is c o n n e c t e d in the feed-back loop of an o p e r a t i o n a l a m p l i f i e r and, further, if a p h o t o - s e n s o r is c o n n e c t e d to the input such that ij becomes ~ (the value of photo-current), the output of the a m p l i f i e r is a voltage w h i c h increases by about 18mV for each d o u b l i n g of the light intensity. Thus, five decades of light v a r i a t i o n may be r e p r e s e n t e d on a voltage scale of only 300mY w h i c h may be suitably scaled and a m p l i f i e d according to a p e r t u r e and f i l m - s p e e d settings. The third a p p r o a c h involves the use of digital techniques. The a v a i l a b i l i t y of c o m p a t i b l e bipolar and I L processes has opened the door to a n a l o g u e / d i g i t a l circuits integrated together on the s a m e chip. The r e q u i r e m e n t s of camera circuits are ideal for such processes - low current consumption, low supply v o l t a g e and low speed. Fig. 13 shows the block d i a g r a m of an a n a l o g u e / d i g i t a l a u t o m a t i c camera circuit which drives a LED dot display to indicate exposure time and may operate with any of the three d i f f e r e n t types of photo--sensors as shown.

Sensor input circuits ",'e,t

o./1,~

Exp°se°'4Circuit~- JSt~'""r~ "]ch*ckl = I

Vstab~

OR

Hold eley

,.q,,e,,,. ] control

- %

flash

o

o,e,e.do

,

| Output | ~Time Driver |~ °~ Indicator .

exposure

o dehq.,d exp.

J

*

t ~

sensor trigger level

~

:

°'""

~_~o

"

exp. OR

LED.Strip

| I

Enable

J

~

o

o

I

current sink Aperture/Film Speed.information

I Fig.

13.

Shutter Relay 1

Block d i a g r a m of an a n a l o g u e - d i g i t a l IC for (preferred-aperture) automatic cameras

Other P h o t o g r a p h i c A p p l i c a t i o n s The t e c h n i q u e s and circuits d e s c r i b e d above may also be applied to c i n e - c a m e r a s w i t h the n o t e a b l e d i f f e r e n c e that e x p o s u r e times are fixed by the f i l m - t r a n s p o r t speed and automatic e x p o s u r e is usually c o n t r o l l e d from the aperture. Fig. 14 shows a s i m p l i f i e d block d i a g r a m of a m u l t i - f e a t u r e c i n e - c a m e r a which contains three separate IC's:- a b i p o l a r w i n d o w - d i s c r i m i n a t o r to s e n s e light

.o Shutter Relay 2

44

D. Anderson

/ ./

pw

.%

\ \

FilmTranspoM "I" Motor [

lg Ape tur(

forwards/reverse forsuperimpose

~b~ttery. _.1level

indicator

sup ape

Fig.

14.

Simplified

circuit diagram of~ a "trick" automatic aperture-control

cine

camera

1

with

variations and control a stepping motor ganged to the aperture, an MOS circuit which generates the switching signals for the stepping motor and controls the various delays and sequences, and a bipolar motor-speed regulator which maintains a constant filmtransport speed and monitors battery level. In the field not yet found

of "computer" widespread

flash devices, integrated application. Fig. 15 shows

energyin capacitor

circuits have the principle

charging _... _ current v I choke

i

4~ flashtube choke ~x firing" ~l quench. ~ thyristor "~ thyristor

energy.storage capacitor

T!,

r I computer [

Ifiring-puisel |generalor I I

I

5.

dischargetimet Fig.

15.

Principle

of

a modern

"computer"

flash

device

ICs take the Cams out of Cameras

45

of a m o d e r n c o m p u t e r flash device and a typical circuit is shown in more detail in fig. 16. Gone is the q u e n c h - t u b e w h i c h e x p e n d e d excess energy w h e n s u f f i c i e n t light has been generated. In its

TXC02A50

1 ~J'''v'. ,,

II

SSiB0640

6,8 ~F

|flHhtube

Ik

chargingcurrent 1000 FF/350V

:2605

10

firingthyristor ~ ~BSt E()433T ~] 5SIC2605 10k

~m

~6 ~.1 BStC0233T( 0.1 FF

22

330 lk i

, ezx55.

~"

c,.,

II

w,

~ ' I 11 k

470

-.45 BP103 B 47k

Fig.

16.

Circuit

diagram of (high-voltage

a modern charging

"computer" flash circuit omitted)

I BCY58/VIII

device

place two thyristors are used w h i c h g u a r a n t e e fast, a c c u r a t e firing and save unused energy in the storage capacitor, thus e n a b l i n g a more rapid recharge cycle for most flash applications. With the use of fast silicon p h o t o - c e l l s in cameras, the p o s s i b i l i t y arises of c o n t r o l l i n g flash exposures using the automatic e x p o s u r e control in the camera itself, thus saving the need for a separate "computer" circuit in the flash device. In p r a c t i c e this proves to be very d i f f i c u l t due to the m e c h a n i c a l delays a s s o c i a t e d w i t h the shutter cycle as shown in fig. 17. Flash devices vary w i d e l y in their c h a r a c t e r i s t i c s and this gives rise to a v a r i e t y of s y n c h r o n i s a t i o n requirements, the two most i m p o r t a n t being shown. The d u r a t i o n of an e l e c t r o n i c flash, for example, is so short that no normal m e c h a n i c a l shutter could respond quickly enough to regulate film exposure.

Advanced Camera Applications One of the most topical p r o j e c t s at the p r e s e n t time, is the d e v e l o p m e n t of a cheap, reliable, sensitive and compact s y s t e m for auto-focussing. Many systems have been p r o p o s e d but the most p r o m i s i n g at present, involves the t r a n s l a t i o n of the familiar s p l i t - i m a g e f o c u s s i n g system to a fully e l e c t r o n i c basis as s u g g e s t e d by the circuit c o n f i g u r a t i o n in Fig. 18 (right). In this e l e c t r o n i c s p l i t - i m a g e c o n f i g u r a t i o n the two images (one of w h i c h is d e p e n d e n t on the lens setting) are p r o j e c t e d onto two identical p h o t o arrays and the c o r r e s p o n d i n g elements are c o m p a r e d in a b r i d g e - t y p e circuit, w h i c h is in balance only when the two images are identical. An a l t e r n a t i v e method o p e r a t e s on the p r i n c i p l e that an in-focus image e x h i b i t s a m a x i m u m c o n t r a s t ratio or, in other words, if the image is scanned by some m e c h a n i c a l means such as the grati,g shown in Fig. 18 (left), a m a x i m u m in the h i g h - f r e q u e n c y content of the output signal indicates an in-focus image. A d i f f e r e n t i a l c o n f i g u r a t i o n helps to cancel out u.R. 18-~I/2--D

46

D. Anderson

4

relative 100 brightress A 75,

av~fiashpe~}0d i

mlm 3 2

/

,

r

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0

k 50 40

20

10

,,,umination characteristic of a magnesium flash .bulb

I

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50 25 0

msec

Illumination characteristic of an electronic flash .lamp

!

/ 0.1 0.2 0.3 0.4 --m,- msec

)j tl/4--t2-.--)j~-t3-~l

radiant flux 0 A

1

_ teff _

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>2.5 ms 14--

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17.

shutter fully open

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Flash synchronisation for betrween-ihe-lens shutters

l

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6 (from Deutsche Offenlegungsschrift 2156 617) Fig.

18.

Automatic

focussing

-

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the background DC content of the image. Further, if the furrowed gratin 9 in Fig. 18 is oscillated in the image plane at a fixed frequency, it is possible to obtain a quantitive focussing error by comparing the phases of the photo-sensor output signals.

"%."

ICs take the Cams out of Cameras

The p o s s i b i l i t y of e l i m i n a t i n g aperture and shutter m e c h a n i s m s by the use of p o l a r i z i n g lenses is not likely to be a c h i e v e d w i t h i n the near future, a l t h o u g h a c o m b i n e d e l e c t r i c a l / m e c h a n i c a l lens and shutter could o v e r c o m e some of the p r o b l e m s a s s o c i a t e d with response time and m a x i m u m opacity. More p r o m i s i n g is the d e v e l o p m e n t of an e l e c t r o - m a g n e t i c storage camera w i t h a solid-state imaging device w h i c h will store p i c t u r e s in the form of m a g n e t i c i n f o r m a t i o n on cards or tape. Solid-state cameras e m p l o y i n g ccd image displays have already been d e m o n s t r a t e d but, the high price of such units at present, prohibits their w i d e s p r e a d a p p l i c a t i o n in the n o n - m i l i t a r y field. W h a t e v e r the realities and p r a c t i c a l i t i e s of such systems, it seems certain that e l e c t r o n i c s will continue to find e x c i t i n g new a p p l i c a t i o n s in the field of p h o t o g r a p h y for some time to come.

47