Projection apparatus for automatic correction of non-uniform illuminance distribution in image area of imaging plane

The present invention provides an apparatus for projecting the image of an original on the projection surface of a screen or photosensitive member, the apparatus having an illumination correction device for changing a distribution of illuminance on the projected surface, the illumination correction device being adapted to process a difference between the amount of a light passing near the center of the projection optical path and the amount of a light passing near the marginal portion of the same optical path to obtain the results on which the illumination correcting device will be controlled to correct any irregularity of the illuminance distribution on the projected surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a projection apparatus for projecting an 
image of an original such as a microfilm, document, book or the like on a 
projection plane in a reader or copying machine. 
2. Description of the Prior Art 
In microfilm readers or reader-printers, an image recorded on a microfilm 
is projected on a screen through a projection lens in an increased 
magnification, this projected image being read as it is or further 
projected on a photosensitive member through the reader printer to obtain 
the copy thereof. 
Since different rates of reduction are generally used when images are 
recorded on microfilms, the magnification of projection must be adjusted 
depending on the microfilms used. 
The prior art variable magnification projection apparatus has such a 
disadvantage that when the magnification is changed to vary the rate of an 
optical path length across a lens, the distribution of light (illuminance) 
on the projected surface of a screen or photosensitive member will vary so 
that fluctuations are brought about with respect to the quality of image 
and the characteristics of the photosensitive member. In order to overcome 
this problem, a slit-exposure type copying machine has been proposed in 
which one of different slit plates is adapted to be inserted across the 
optical path on each change of magnification. Such a copying machines has, 
however, various disadvantages in that a mechanical structure, for 
example, the one for detecting the change of magnification, becomes more 
complicated and is increased in size, and in that the copying machine as a 
whole becomes more complicated since the shape of each slit plate must 
delicately be varied, and that the copying machine becomes expensive. 
It has been also proposed that the distribution of light emission in an 
original illuminating lamp is changed depending on the change of 
magnification. However, this proposal does not provide the sufficient 
correction. 
It has been also proposed that the distribution of illuminance on the 
projected surface be corrected by moving a condenser lens or lamp in 
connection with the change of magnification. Such a proposal also includes 
a disadvantage in that various mechanisms for detecting the changed 
magnification and for moving the lens or lamp in connection with the 
change of magnification will increasingly be complicated and increased in 
size as the number of selectable magnifications increases. 
It has been further proposed that the magnification can be changed by 
selecting one of different lenses. In this case, it is required to utilize 
a so-called Kohler illumination for imaging the filament of an 
illumination lamp on the film-side pupil of a projection lens to 
effectively illuminate a group of exchangeable lenses. If the illumination 
is not proper, the light illuminating the projection lens may extremely be 
reduced in amount or unevenness may be brought about in the amount of 
light. 
For such a reason, if the difference between one magnification and another 
magnification is smaller on projection, the distance of the film-side 
pupil from the surface of a film can be designed to be invariable for 
various different lenses to be used. If the difference in magnification is 
larger on projection, however, the pupil of the projection lens cannot be 
designed in the same manner. This also results in an increase in cost. A 
method is normally carried out in which the image of the filament in the 
illumination lamp is formed at the position of the film-side pupil in the 
projection lens by moving the condenser lens depending on the properties 
of the projection lens. 
Such a method has, however, disadvantages in that a proper matching is hard 
to obtain since the position of the condenser lens is determined by 
eye-measurement, that an unskilled person may fail to match the position 
of the condenser lens to the property of the projection lens so that an 
obscure image will be observed with an effort, and that an unevenness may 
be produced in the density of copied images due to the unevenness of 
illumination to take wasteful copies in a printer. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the above 
disadvantages in the prior art. 
Another object of the present invention is to enable an image having less 
unevenness in brightness for observation and to obtain a copy having less 
irregularity in density. 
A further object of the present invention is to provide an illumination 
suitable to a magnification to be used, even if the magnification is 
changed on projection. 
A further object of the present invention is to provide a projection 
apparatus of a simple construction which can automatically equalize the 
distribution of illuminance even if the magnification on projection is 
more broadly changed. 
The present invention will now be described with reference to embodiments 
which are illustrated in the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a reader-printer according to the present invention, which 
includes an upper casing 101 and a lower casing 102. Within the lower 
casing 102 are disposed a spherical reflection mirror 99, a lamp 103, a 
filter 100, a condenser lens 104, a reflector 105 and another condenser 
lens 106, all of which define an illuminating system. Within the upper 
casing 101 are disposed an optical system including a projection lens 107 
and a half mirror 108; a reflection type screen receiving the light 
reflected by the mirror 108; a copy sheet supply cassette 110; a charger 
112; copy sheet feeding means comprising feed rollers 111, a drive belt 
113, a supply roller 135 and feed rollers 145, 146, 148; and development 
means including a tank of developing liquid 114, an development roller 115 
and others. Between the second condenser lens 106 and the projection lens 
107 is located a microfiche carrier 116 which holds two sheet glasses 
G.sub.1 and G.sub.2 with a microfiche film located therebetween. The 
carrier 116 is adapted to move on the lower casing 102. When the carrier 
106 is moved in all the directions by operating an actuating handle 117, 
the microfiche film moves with the carrier as a unit to position the 
particular frame of the film in the optical path of projection. 
The upper casing 101 includes an opening formed therein at the forward face 
for observing the interior of the casing 101. The opening is provided with 
a shutter 118 for closing the opening. If a projected image is to be 
copied, the shutter 118 blocks any external light into the upper casing 
through the observation opening. Atlernatively, the shutter may be 
replaced by a member functioning to control a light from a projected image 
so that the light can be transmitted therethrough when the image is 
observed. Such a member includes a filter or closing plate of a material 
which can vary in spectral transmission factor when a voltage is applied 
thereto, such as a liquid crystal or an electrochromic substance. 
The filter may suitably be colored to optimize the contrast in an image 
projected on a screen when the image is ovserved through the filter. The 
filter may be, for example, of "Varad" (trade mark possessed by Marks 
Polarized Corp.). The "Varad" filter is in the form of a plate which 
includes a dipole suspended between a pair of transparent electrodes. When 
a voltage is applied between the pair of electrodes, the dipole is 
rearranged perpendicular to the electrodes to permit the plate to transmit 
the light. If the electrodes are deenergized, the dipole is brought into a 
scattering state to block any light through the plate. 
When the machine is in its read mode, the shutter 118 is in its light 
transmitting state and the screen 109 is placed at a projection plane on 
which an image in the film is imaged. As a result, the image projected on 
the screen can be read through the observation opening. 
The reflection type screen 109 is used to read an optical image incident on 
the forward face thereof from the same side of the screen. The screen 109 
is in the form of a sheet of paper having a light-diffusive surface or a 
white-colored cloth having a roughed surface which is mounted at one side 
on the drive belt 113 for carrying copy sheets to move therewith or in the 
form of a drive belt to which a light-diffusive material is applied at one 
side. The drive belt 113 includes a positioning aperture 121 formed 
therein. When this aperture 121 is detected by a microswitch SW.sub.2, the 
drive belt is stopped to position the screen 109 at a position shown by 
solid line in FIG. 1. At this time, the screen 109 will be placed in a 
projected plane. Another microswitch SW.sub.1 is located near the marginal 
portion of the exposed plane and serves to detect a copy sheet fed 
thereto. 
Copy sheets S are contained in a supply cassette 110 one above another. The 
copy sheet may be of a so-called electrofax paper which is coated with 
zinc oxide. If a copy instruction is inputted by operating a copy button, 
the known supply roller 135 begins to rotate to feed one of the copy 
sheets S out of the cassette 110 into the nip between the feed rollers 111 
and to move that copy sheet to the charger 112 by means of the rotating 
feed rollers 111. The fed copy sheet is uniformly charged by the charger 
112 to have a photosensitive property. Subsequently, the charged copy 
sheet is fed onto the surface of the drive belt 113 through a guide plate 
137 by incorporation of the drive belt 113 with a guide roller 136. The 
drive belt 113 is endless and passed over the rollers 138, 139 and a drive 
roller 140 to form a triangle shape. The drive roller 140 is connected to 
a drive to move the belt 113 when the drive is energized. The belt 113 is 
adjusted by a roller 141' with respect to tension. The surface of the 
drive belt 113 includes a plurality of slots formed therethrough in 
several rows. A suction device is disposed within the triangle defined by 
the belt 113 and positioned at a position opposing to the oblique side of 
the triangle. The suction device 141 includes a plurality of suction 
openings formed therein at the side of the suction device opposing to the 
belt 113 and is connected with a blower 142. 
When the blower 142 is energized, a copy sheet S supplied onto the run of 
the belt 113 corresponding to the oblique side of the triangle by 
incorporation of the belt 113 with the guide roller 136 is drawn toward 
the surface of the drive belt 113 under the action of the suction device 
141 and then moved to the projected plane as the drive belt is moved. 
The projected plane is substantially at a position corresponding to the 
oblique face of the drive belt 113. Although the screen is about one 
millimeter thick and a copy sheet S is about 0.1 millimeters thick, the 
screen and copy sheet are positioned within the focal depth of a lens if 
an image is focused in the projected plane through the optical system, so 
that the lens is not required to be adjusted at each change of mode. 
If the leading edge of the copy sheet S is brought into contact with the 
microswitch SW.sub.1, the drive belt 113 is deenergized. On the other 
hand, the shutter 118 is changed to its light blocking state in accordance 
with a copy instruction. Thus, the machine will be changed from its read 
mode to its copy mode. 
When the copy sheet S is placed on the projected plane, an image in the 
film is projected thereon. On termination of the exposure, the belt 113 is 
again energized to move the copy sheet S on which a latent image is formed 
by the exposure, upwardly along the oblique run of the drive belt toward 
the nip between the belt and a pinch roller 143. After leaving the nip 
between the drive belt and the pinch roller, the copy sheet S is moved 
along a guide plate 144 to the nip between the feed rollers 145. On the 
other hand, the drive belt 113 continues to move. When the positioning 
aperture 121 in the belt 113 is detected by the microswitch SW.sub.2, the 
drive belt is stopped. Thus, the screen is re-positioned in the projected 
plane. At the same time, the shutter 118 is changed to its light 
transmitting state. By the feed rollers 145, the copy sheet S is moved to 
the development roller 115 whereat it is developed, and then to the gap 
between guide plates 147. Thereafter, the copy sheet S is exhausted from 
the exit 149 of the upper casing 101 to a tray 150 supported by the lower 
casing 102 by means of exhausting rollers 148. Further details are omitted 
since the above process for forming the image is known in the art. 
Light from the illumination lamp 103 passes through the filter 100 and the 
first condenser lens 104 and then turned to the second condenser lens 104 
through 90.degree. by the reflection mirror 105. After passing through the 
second condenser lens 106, the light is focused on the film-side pupil of 
the projector lens 107 located above the condenser lens 106 to form an 
image of the filament in the illumination lamp 103. The projection lens 
107 can be replaced by one of various lenses having different focal 
lengths to change the magnification on projection. These interchangeable 
lenses are so designed that the film-side pupils thereof are substantially 
in the same position to always provide a substantially invariable 
brightness (illuminance) in the projected plane even if one of the lenses 
is replaced by the other. 
Behind the half mirror 108, there are located a first photoelectronic 
converter (i.e., photoelectric converter) element 200 at a position 
substantially corresponding to the optical axis of the projection lens 107 
and a second photoelectronic converter element 201 at a position 
substantially corresponding to one of the marginal portions of the 
projection lens 107. 
FIG. 2 shows the details of the illumination section in which the filter 
100 is fixed to a support block 217. The block 217 includes a threaded 
aperture formed therethrough, into which the threaded section 219a of a 
screw rod 219 directly connected with a reversible motor 218 is screwed. 
When the motor 218 is energized to rotate the screw rod 219, the rotation 
thereof causes the block 217 to move along the screw rod 219. Thus, the 
filter 100 is reciprocated along the optical axis of the optical path of 
illumination between the lamp 103 and the first condenser lens 104. Limit 
switches 220 and 221 are located at the opposite ends of movement in the 
block 217 to limit the movement thereof in the opposite directions. 
The filter 100 is in the form of a circular density filter which has the 
least spectral transmission factor at the center thereof, this spectral 
transmission factor being gradually increased from the center to the 
periphery of the filter. FIG. 3 shows such a change of the filter in 
spectral transmission factor. 
FIG. 4 shows a block diagram of a control circuit for correcting a 
distribution of illumination in the projected plane. In FIG. 4, the 
control circuit comprises photoelectronic converter elements as shown by 
200, 201 in FIG. 1; a reduction circuit 223 for processing a difference 
between the output voltages from the first and second photoelectronic 
converter elements 200, 201; a bias circuit 224 for applying a bias 
voltage to the output of the reduction circuit 223 so that the results in 
the reduction circuit 223 will be maintained positive; a peak detection 
circuit 225 for sensing the peak in the output signal from the bias 
circuit 224; a motor drive circuit 226 for controlling the rotation of the 
motor 218 shown in FIG. 2; a rotational direction changing circuit 227 for 
generating at its output a signal used to change the rotational direction 
of the motor 218 when receiving the outputs from the limit switches 220 
and 221 shown in FIG. 2; and a start instruction switch 228 for actuating 
the peak detection circuit 225 and for generating at its output a start 
signal used to energize the motor 218. 
FIGS. 5A through 5D illustrate the output signals from the various sections 
in the above control circuitry when no film is inserted into the carrier 
116, the lamp 103 is turned on and the filter 100 has been moved to a 
position Z from a position X shown in FIG. 2. In these figures, the 
horizontal axis represents the position of the filter while the vertical 
axis represents the output voltage of the block. In FIG. 5A, a curve 200' 
represents the output voltage from the first photoelectronic converter 
element 200 while a curve 201' represents a change in the output voltage 
from the second photoelectronic converter element 201. Each of the 
photoelectronic converter elements 200 and 201 provides an increased 
output voltage when receiving more light. FIG. 5B shows the output of the 
reduction circuit 223, FIG. 5C illustrates the output of the bias circuit 
224, and FIG. 5D represents the output of the peak detection circuit 225. 
The machine will be operated as follows: Assuming that the lamp 103 is 
turned on by an operator through a power switch (not shown) with no film 
inserted into the fiche-carrier 116 and that the filter 100 is in the 
position (X) shown in FIG. 2. The first and second photoelectronic 
converter elements 200 and 201 generate output voltages (a) and (b) on the 
point (X) in FIG. 5A, respectively. The reduction circuit 223 processes 
the difference between the output voltages (b) of the second 
photoelectronic converter element 201 and the output voltage (a) of the 
first photoelectronic converter element 200. The resulting value (b-a) 
becomes a voltage c as shown in FIG. 5B. The bias circuit 224 applies a 
constant bias voltage to the output of the reduction circuit 223 to 
convert the negative output voltage c from the reduction circuit 223 into 
a positive voltage d as shown in FIG. 5C. This output of the bias circuit 
224 is supplied to the peak detection circuit 225. 
Next, if the start switch 228 is depressed by the operator, a start signal 
is generated to energize the motor 218 through the motor drive circuit 
226. At the same time, the peak detection circuit 225 begins to operate. 
Thus, the filter 100 begins to move in the direction of arrow M (FIG. 2). 
The movement of the filter changes the outputs of the first and second 
photoelectronic converter elements 200 and 201, the reduction circuit 223, 
the bias circuit 224 and the peak detection circuit 225 as shown in FIGS. 
5A to 5D. These changed outputs correspond to the position of the filter. 
When the difference between the outputs of the two photoelectronic 
converter elements 200, 201 reaches its minimum value, the distribution of 
illuminance on the projected plane (or the film surface) has the least 
unevenness. This means that the filter is properly positioned. In other 
words, when the filter 100 reaches the point (Y), a peak (it is produced 
when the difference between the outputs of the photoelectronic converter 
elements 200, 201 has the least value) is detected by the peak detection 
circuit 225 which in turn generates a peak detection signal e. This peak 
detection signal is used to deenergize the motor 218 through the motor 
drive circuit 226. In this manner, the distribution of illuminance will 
most be equalized on the projected plane. This means that the illumination 
system is properly set. Therefore, the operator can insert a film into the 
fiche-carrier 116 to observe the film under optimum conditions. 
Although the description has been made as a peak value is detected 
immediately after the motor has been energized, the block 217 may be 
engaged by the limit switch 220 or 221 if the filter is moved from an 
inproper start position in an inproper direction. In such a case, a 
reversal signal is supplied to the rotational direction changing circuit 
227 which in turn generates a signal for changing the rotational direction 
in the motor. This signal is applied to the motor drive circuit 226 to 
reverse the rotation of the motor 218. Thereafter, the above peak 
detection is continued. When a peak is detected, the motor 218 is 
deenergized. 
Although the illustrated embodiment has been described as to initiate the 
rotation of the motor in one direction and then reverse the rotation by 
the limit switch if no peak is detected in the one direction, the output 
of the reduction circuit 223 may be used to compare the present value with 
the preceding value to determine the rotational direction of the motor so 
that the peak value can be detected always through the minimum distance. 
For example, the first output of the reduction circuit before the motor is 
energized is compared with the second output of the same immediately after 
the motor is rotated only a little. If the second output is larger than 
the first output, the motor continues to rotate in the same direction. If 
the second output is smaller than the first output, the rotation of the 
motor is reversed. 
In the illustrated embodiment, the filter is disposed between the lamp and 
the first condenser lens. However, the filter may be located between the 
second condenser lens and the supporting surface on which the film is 
placed. 
FIG. 6 shows the other embodiment of the filter in which a plurality of 
filtrating elements 300.sub.1 -300.sub.9 are located on a disc 301 in a 
circle. The disc 301 is connected with a motor and rotated by the same 
about a shaft 302 to bring the selected one of the filtrating elements 
into alignment with the illumination path between the lamp 103 and the 
first condenser lens 104. The filtrating elements 300.sub.1 -300.sub.9 are 
different from one another in the distribution of intensity for 
transmitted light. In FIG. 6, areas denoted by a number of dots are lower 
in spectral transmission factor. In each of such areas, the spectral 
transmission factor increase gradually from the center to the periphery. 
The motor for driving the disc 301 is controlled based on the difference 
between the outputs of two photoelectronic converter elements 200 and 201 
to select a filtrating element for providing a desired distribution of 
illuminance on the projected plane. 
FIG. 7 shows a further embodiment of the illumination section for 
correcting the distribution of illuminance in which similar parts are 
designated by similar numerals. The illumination section of FIG. 7 is 
different from that of FIG. 2 in that a filter 400 shown in FIG. 7 is 
disposed between the first condenser lens 104 and the second condenser 
lens 106 and that the structure of the filter itself is different from 
that of the filter shown in FIG. 2. Moreover, the filter 400 is 
stationary. FIG. 8 is a front elevational view of the filter 400 and FIG. 
9 is a cross-section of the same. The filter 400 includes a plurality of 
annular discoloring plates a-g which are disposed concentrically relative 
to one another and spaced apart from one another so that one plate can 
become transparent or opaque independently of the others. The filter 400 
is located in the illumination path through which a collimated beam of 
light passes. As seen from FIG. 9, each of the discoloring plates includes 
a liquid crystal element (403a, 403b . . . 403g) located between a first 
transparent electrode (401a, 401b . . . 401g) and a second transparent 
electrode (402a, 402b . . . 402g). Preferably, the filter 400 may be 
located at a position spaced away from the lamp 103 rather than the second 
condenser lens 106. Further, a heat insulating filter may preferably be 
disposed in front of the filter 400. If a voltage is applied between the 
opposed electrodes (for example, 401a and 402a), a liquid crystal (403a) 
therebetween discolors to make the corresponding discoloring plate (a) 
opaque. If no voltage is applied, the discoloring plate is transparent. 
When the discoloring plate becomes opaque, the transmission of light 
therethrough is reduced. If the discoloring plates are selectively changed 
in color from the center to the periphery of the filter 400, the whole 
filter 400 is changed with respect to its distribution of intensity for 
transmitted light. 
FIG. 10 shows a control circuit for changing the filter 400 with respect to 
the distribution of intensity for transmitting light. In FIG. 10, the same 
parts as in FIG. 4 are omitted. The control circuit includes a liquid 
crystal drive circuit 410 connected to the peak detection circuit 225 and 
start instruction switch 228 as shown in FIG. 4. The liquid crystal drive 
circuit 410 is connected to a group of electric terminals 405 1eading to 
the pairs of electrodes (hereinafter called a', b', c', e', f' and g') in 
the discoloring plates a-g. Voltage is applied to these electrodes a'-g' 
in the order as described. Once a voltage is applied to a pair of 
electrodes, these electrodes continue to be energized even after a voltage 
has been applied to another pair of electrodes. After all the electrodes 
a'-g' have been energized, they are deenergized. Subsequently, voltage is 
again applied to the electrodes in the order from a' to g'. Such 
application of voltage will be repeated. If a peak signal is outputted 
from the peak detection circuit 225, the application of voltage is stopped 
at the last energized electrodes. 
In the above-mentioned embodiment, if the image in a film is projected on 
the projected plane in which a screen or photosensitive sheet is placed, 
for example, through a projection lens having a short focal length, only a 
narrow area in the film (hereinafter called effective projection area) is 
projected on the projected plane in high magnification since the distance 
between the film and the projected plane is constant. Since at this time, 
the difference between the outputs of the first and second photoelectronic 
converter elements 200 and 201 is smaller, voltage is applied to one or 
more discoloring plates near the center of filter 400 to make them opaque 
near the center of the effective projection area so that the amount of 
light passing near the center of the optical illumination path will be 
decreased to equalize the distribution of illuminance on the projected 
plane without any change of areas other than the center of the optical 
illumination path with respect to the amount of light. On the contrary, if 
the image in the film is projected on the projected plane by the use of a 
projection lens having a longer focal length, the effective projection 
area in the film is increased so that the difference between the outputs 
of the first and second photoelectronic converter elements 200 and 201 
will be increased. Voltage is therefore applied to discoloring plates more 
than those in the above-mentioned case at and near the center of the 
filter 400 so that they will be opaque at the center and surrounding 
region of the effective projection area. The amount of light will be 
reduced at the center and surrounding region of the optical illumination 
path to equalize the distribution of illumination on the projected plane. 
The other region of the optical illumination path remains constant with 
respect to the amount of light. 
In addition to the liquid crystal, the material of the discoloring plates 
includes any other material which can vary with its spectral transmission 
factor when a voltage is applied thereto, such as electrochromic 
substance, photochromic substance, Varad or the like. The spectral 
transmission factor in each discoloring plate, for example, of liquid 
crystal may be changed by changing the voltage to be applied to the pair 
of transparent electrodes in the corresponding discoloring plate. 
Furthermore, the filter 100 of FIG. 2 may be combined with the filter 400 
of FIG. 7 to correct any unevenness in the distribution of illuminance on 
the projected plane. 
The positions of the first and second photoelectronic converter elements 
for measuring the amount of light are not limited to the illustrated 
arrangements. Although the photometry and control have been initiated by 
operating the start instruction switch in the aforementioned embodiments, 
they may be initiated by generating a start instruction signal at the same 
time as a power switch is turned on or as a projection lens is replaced by 
another projection lens to change the magnification. 
FIG. 11 shows an example of the peak detection circuit which comprises a 
delay circuit 450 for delaying the output of the bias circuit 224 and a 
comparator 451 for comparing the output of the bias circuit 224 with that 
of the delay circuit 450. The comparator 451 is adapted to generate a peak 
signal at its output if the relationship between two input signals is 
reversed in magnitude. The peak detection circuit can be replaced by one 
of the conventional peak detection circuits. 
Although the magnification has been changed by replacing a projection lens 
with another projection lens in the afore-mentioned embodiments, it may be 
changed by using a fixed focus lens to change its optical path or by using 
a zoom lens. 
If the position of the film-side pupil in a projection lens is extremely 
fluctuated on changing the magnification, the condenser lenses or the 
illumination lamp may be re-positioned. 
FIG. 12 shows a further embodiment of the illuminating section according to 
the present invention in which in combination with the filter of FIG. 7, 
an illuminating lamp may be moved to correct the distribution of 
illuminance. 
FIG. 13 shows a control circuit used in the illumination section shown in 
FIG. 12. In FIGS. 12 and 13, parts similar to those in the afore-mentioned 
embodiments are designated by similar numerals. 
In FIG. 12, a lamp 103 and spherical reflection mirror 99 are supported by 
a block 317 which includes a threaded opening formed therethrough. A screw 
rod 319 has a threaded portion 319a which threadedly screwed into the 
threaded opening of the block 317. The screw rod 319 is connected to a 
reversible motor 318 and rotated by the same. As the rod 319 is rotated by 
the motor 318, the block 317 moves along the screw rod 319. The lamp 103 
and mirror 99 move together with the block as a unit to change the 
position in which the filament in the lamp 103 is to be imaged. The range 
in which the block 317 moves is defined by limit switches 320 and 321 as 
in FIG. 2. The control circuit comprises a motor drive circuit 326 as in 
FIG. 4. Upon receiving an output of the peak detection circuit 225, the 
motor drive circuit 326 controls the motor 318. The control circuit also 
comprises a rotational direction changing circuit 327 for generating at 
its output a signal used to change the rotational direction of the motor 
318 when receiving the outputs of the limit switches 320 and 321 and a 
liquid crystal drive circuit 310 for applying voltage to electrodes a', 
b', . . . g' of the discoloring plates in the filter 400 shown in FIG. 11. 
When a start signal from the start instruction switch 228 is received, the 
liquid crystal drive circuit 310 is adapted not to energize all the 
electrodes a', b' . . . g'. If the liquid crystal drive circuit 310 
receives a motor stop signal (described hereinafter) from the motor drive 
circuit 326, it successively energizes the electrodes in the order from a' 
to g'. After the motor stop signal has been generated and when the peak 
detection circuit 225 generates a peak signal, the application of voltage 
is stopped at the lastly energized electrodes. 
In FIGS. 12 and 13, the peak detection circuit 225 and the motor drive 
circuit 326 are actuated by operating the start instruction switch 228 to 
energize the motor 318. On the other hand, the liquid crystal drive 
circuit 310 does not energize all the electrodes a', b' . . . g' even when 
the start instruction switch 228 is turned on. As a result, the whole 
filter 400 remains transparent. If the lamp 103 is moved by the motor 318 
and when the difference between the outputs of the first and second 
photoelectronic converter elements 200 and 201 reaches its minimum value, 
the peak detection circuit 225 generates a peak signal which is in turn 
used to stop the motor 318. Thus, the lamp 103 is positioned at a location 
in which the filament of the lamp 103 is imaged near the film-side pupil 
of the projection lens. As a result, the illuminance on the projected 
plane is corrected irrespective of any change in magnification. As the 
motor 103 is stopped, the motor drive circuit 326 generates a motor stop 
signal at the output terminal 326a thereof. This motor stop signal is used 
to reset the peak detection circuit 225 and then re-start the same. With 
this motor stop signal, the liquid crystal drive circuit 310 is actuated 
so that voltage is successively applied to the electrodes a' to g' as in 
FIG. 10. If voltage is applied to the selected electrodes, the peak 
detection circuit 225 generates a peak signal at the output thereof so 
that the application of voltage will be stopped at this point of time. 
On changing the magnification, thus, the distribution of illuminance can 
exactly be corrected only through two correction operations, that is, the 
first operation based on the movement of the lamp 103 and the second 
operation based on the control of the filter 400 with respect to the 
spectral transmission factor thereof. 
The movement of the lamp may be replaced by the movement of the condenser 
lenses along the optical illumination path or the selection of plural 
condensers having different focal lengths which are disposed in the 
optical illumination path. Further, the filter 400 may be replaced by one 
of the filters shown in FIGS. 2 and 6. 
FIG. 14 shows another embodiment of the reader-printer according to the 
present invention and which comprises a reader casing 501. The casing 501 
includes a fiche-carrier 502 mounted thereon which holds two confining 
glass plates 503 and 504 with a microfilm F being placed therebetween. 
Thus, each frame in the microfilm can selectively be projected. An 
illumination lamp 505 is disposed below the fiche-carrier 502. Light from 
the lamp 505 is passed through a first condenser lens 507 and a second 
stationary condenser lens 507 and then turned by a stationary reflection 
mirror 509 through 90.degree. toward a third fixed condenser lens 510. 
After passing through the third condenser lens 510, the light is incident 
on the film-side pupil of a projection lens 511 located above the 
fiche-carrier 502 to image the filament of the illumination lamp 505 
thereon. The projection lens 511 may be replaced by one of the other 
projection lenses having different focal lengths in connection with a 
magnification to be selected. A spherical reflection mirror 506 is 
disposed behind the lamp 505 to collect the light from the lamp 505 for 
effectively utilizing it. 
An image in the microfilm F contained in the fiche-carrier 502 is enlarged 
through the projection lens 511 and then reflected by first and second 
reflection mirrors 512 and 513 toward a projection screen 514 mounted on 
the casing 501 whereat the image can be observed. The first reflection 
mirror 512 is fixed to the upper face of the reader casing 501 while the 
second reflection mirror 513 is fixed to the side of the same. Behind the 
first reflection mirror 512, a photoelectronic converter element 515 is 
located on the optical axis and another photoelectronic converter element 
516 is disposed adjacent the marginal portion of the mirror 512. 
Referring to FIG. 15, the first condenser lens 507 is fixedly mounted on a 
lens fixing block 517 including a threaded aperture 517a formed 
therethrough. This threaded aperture 517a threadedly receives the threaded 
portion 519a on a screw rod 519 which is directly connected with a motor 
518. As the motor 518 is energized, the lens fixing block 517 can move 
along the screw rod 519. The range in which the lens fixing block 517 
moves is determined by limit switches 520 and 521. 
FIG. 16 is a block diagram of a control circuit for the illumination 
section of the reader-printer shown in FIG. 15. 
If the illumination lamp 505 is lighted through a power switch (not shown) 
with no microfilm F being inserted into the fiche-carrier 502 and when it 
is assumed that the first condenser lens 507 is in a position (X) (see 
FIG. 15), the photoelectronic converter elements 515 and 516 disposed 
behind the first reflection mirror 512 generate output voltages (A') and 
(B'), respectively. A reduction circuit 523 shown in FIG. 16 processes the 
output voltage of the photoelectronic converter element 516 minus the 
output voltage of the photoelectronic converter element 515 (B'-A'). A 
bias circuit 524 (FIG. 16) provides a negative output voltage by a 
constant bias applied thereto. This negative output voltage is converted 
into a positive output voltage which is supplied to a peak detection 
circuit 525 (FIG. 16). Unless the peak detection circuit 525 detects a 
peak signal, it remains inoperative with its output being zero. 
If a start instruction switch 522 is turned on, a start signal is generated 
to actuate a motor drive circuit 526 (FIG. 16) to initiate the rotation of 
the motor 518. At the same time, the peak detection circuit 525 (FIG. 16) 
begins to operate. Thus, the first condenser lens 507 begins to move in a 
direction shown by an arrow M. 
If the difference between the outputs of the central and peripheral 
photoelectronic converter elements reaches its minimum value, it is judged 
that the illumination position is properly selected. As the first 
condenser lens 507 reaches a position (Y), a peak is detected by the peak 
detection circuit 525. As a result, a stop signal is generated and 
supplied to the motor drive circuit 526 (FIG. 16) to deenergize the motor 
518. In this manner, the illumination system is properly positioned. 
Subsequently, a microfilm F is inserted into the fiche-carrier 502 so that 
it can be observed under optimum conditions. 
Although the peak value can be detected immediately after the motor has 
been energized in the above-mentioned embodiment, the lens fixing block 
517 may be brought into engagement with the limit switch 520 or 521 if the 
first condenser lens 507 is not properly positioned and then moved in an 
inproper direction. At this time, a signal is applied to the rotational 
direction changing circuit 527 (FIG. 16) to generate a signal used to 
change the rotational direction of the motor. This signal is supplied to 
the motor drive circuit 526 to reverse the rotation of the motor 518. 
During this operation, the peak detection is continued. As a peak is 
detected, the motor 518 is stopped. 
Although the above-mentioned embodiment has been described as to first 
rotate the motor in one direction and then reverse the rotation of the 
motor if no peak value is detected, the output of the reduction circuit or 
bias circuit may be utilized to process the present value and the 
preceding value to determine the rotational direction of the motor so that 
a peak value can always be obtained at the minimum distance. 
The present invention can be applied to film readers, reader-printers and 
copying machines using originals in documents, books and others and 
further to either of the slit-exposure type or whole and coincidental 
exposure type copying system. 
FIG. 17 shows a further embodiment of the present invention in which in 
place of the photoelectronic converter elements located behind the first 
reflection mirror 512 as shown in FIG. 14, lenses 530, 532 and 
photoelectronic converter elements 531, 533 are located between a first 
and second reflection mirrors 512 and 513. The amount of light on the 
center and periphery of a screen is measured by the combination of the 
lens system with the photoelectronic converter elements to detect a peak. 
The measurement of light may be effected in any area other than the above 
position. 
Although the afore-mentioned embodiments have been described as to move the 
condenser lenses, a plurality of condenser lenses having different focal 
lengths may be mounted on a movable platform so that the desired one of 
the condenser lenses can be selected by moving the platform. 
In the readers, copying machines and others in which it is required to 
change the magnification, the present invention can automatically provide 
an optimum state of illumination for each magnification on projection so 
that a clear and good image having no unevenness in illuminance can be 
observed or that a copy image having no unevenness in density can be 
obtained. 
If the image projecting area on the projected plane is changed in magnitude 
on each change of magnification, the first and second photoelectronic 
converter elements may be displaced to detect the amount of light on the 
central and peripheral sections of the image projecting area.