Image-forming apparatus and magnification correction method using the same

An image-forming apparatus includes an image-forming unit for image-forming image information of an original on a record medium, an optical-path-length varying unit for varying a distance between an object and an image, a driving unit for driving the image-forming unit and the optical-path-length varying unit in an interlocking manner such that the image information of the original is formed on the record medium at a plurality of magnifications, and a control unit for controlling the driving unit. In the structure, the image-forming unit and the optical-path-length varying unit are mounted to the driving unit such that the positions of the image-forming unit and the optical-path-length varying unit are adjustable relative to the driving unit. An appropriate magnification is obtained even if a focal length of the fixed-focus image-forming lens fluctuates due to errors occurring during its manufacturing process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image-forming apparatus and a 
magnification correction method using the image-forming apparatus. In 
particular, the present invention relates to an art in which a 
predetermined magnification (a set magnification) and an actual 
magnification are substantially coincident with each other and an accuracy 
of the magnification is improved by using a correction means or a 
correction method for obtaining an appropriate magnification even if a 
focal length, or the like, of a fixed-focus image-forming lens for forming 
image information on a record medium fluctuates due to errors occurring 
during its manufacturing process. 
2. Related Background Art 
FIG. 1 illustrates a main portion of a conventional copying machine or an 
image-forming apparatus with a variable power optical system for varying 
the magnification. In FIG. 1, reference numeral 191 denotes a glass plate 
for supporting an original, and an original (not shown) is put on the 
glass plate 191. Reference numeral 151 denotes a first mirror unit or a 
full-speed mirror unit, and the first mirror unit 151 includes a light 
source or a lamp 151a, light condensing means or shell-shaped reflectors 
151b, a path-bending mirror 151c, etc. Reference numeral 161 denotes a 
second mirror unit or a half-speed mirror unit, and the second mirror unit 
161 includes two path-bending mirrors 161a and 161b. A ratio between scan 
speeds of the first and second mirror units 151 and 161 is 2:1, and those 
mirror units 151 and 161 are moved in a horizontal or sub-scan direction 
relative to the glass plate 191 to scan the entire range of the original. 
Reference numeral 100 denotes a fixed-focus image-forming lens which acts 
as an image-forming means, and the lens 100 image-forms image information 
of the original on a photosensitive drum 181, which acts as an image 
carrier, at a predetermined magnification. Reference numeral 141 denotes a 
zoom-mirror unit or an optical-path-length varying means for varying the 
distance between an object and an image, and the zoom-mirror unit 141 
includes two path-bending mirrors 141a and 141b. Reference numeral 171 
denotes a path-bending mirror. Reference numerals 143 and 144 are 
respectively driving means or variable power driving systems, and those 
driving systems 143 and 144 respectively drive the image-forming lens 100 
and the zoom-mirror unit 141 to positions corresponding to a desired 
magnification, on the basis of signals supplied from a driver control 
means (CPU) 142. 
In FIG. 1, illumination light from the light source 151a is condensed by 
the light-condensing means 151b and illuminates the original put on the 
glass plate 191. The optical path of image information of the illuminated 
original is bent by the path-bending mirrors 151c, 161a and 161b, and the 
image information is image-formed on the photosensitive drum 181, through 
the path-bending mirrors 141a, 141b and 171, by the image-forming lens 
100. The image of the image information of the original formed on the 
photosensitive drum 181 is transferred to a copying paper using a 
well-known electrophotographic process (not shown). 
When the image information of the original is to be copied at a desired 
magnification in the above-discussed copying machine or image-forming 
apparatus, the image-forming lens 100 and the zoom-mirror unit 141 are 
moved to positions corresponding to the desired magnification, by the 
respective driving means or variable power driving systems 143 and 144 
which are controlled by the driver control means 142. For example, when 
the magnification is to be changed from one-to-one magnification to a 
magnification of m, movement amounts x and y of the image-forming lens 100 
and the zoom-mirror unit 141 can be obtained by the following manner. 
With a length between principal planes of the image-forming lens 100 and 
defocus characteristics being disregarded, the movement amount x.sub.m of 
the image-forming lens 100 is given by: 
EQU x.sub.m =f(1/m-1) (1) 
The change amount y.sub.m of the optical path length in this case is 
represented by: 
EQU y.sub.m =f(m+1/m-2)=(x.sub.m -f+f.sup.2 /(x.sub.m +f)) (2) 
f: focal length (design value) of the image-forming lens 
m (m&gt;0): image-forming magnification 
The distance between the original surface and the front principal plane of 
the image-forming lens 100 is given by: 
EQU a=f(1/m+1)=2f+x.sub.m ( 3) 
The distance between the light reception surface and the rear principal 
plane of the image-forming lens 100 is given by: 
EQU b=f(m+1)=2f-x.sub.m +y.sub.m ( 4) 
The structure of the copying machine is designed such that the positions of 
the image-forming lens 100 and the zoom-mirror unit 141 on the optical 
axis are moved by predetermined amounts in accordance with the above 
relations (1) and (2) when the magnification is a desired value of m. 
In the conventional copying machine or image-forming apparatus with the 
variable power optical system, however, the following problems occur. 
For example, there is a problem that the focal length of the image-forming 
lens, whose focal length is designed at f, is liable to fluctuate from the 
design value f by several percent due to the index of employed glass 
material, ground surface precision of the lens surface, central thickness 
of the lens, intervals between the lenses and the like. Due to the 
fluctuation of the focal length f, deviation of a magnification from the 
set magnification occurs as follows. 
It is assumed that an actual focal length f' of the image-forming lens is 
f'=kf due to the errors during the manufacturing process. In this case, 
when adjustments of focussing and magnification are executed at a 
one-to-one magnification, the following relation is obtained: 
EQU a'=2f'=b' 
When the structure is instructed to obtain the magnification of m and the 
optical systems are displaced, the following relations are established: 
EQU a.sub.m '=2f'+x (5) 
EQU b.sub.m '=2f'-x+y (6) 
At this moment, the actual magnification m' of the structure Is represented 
by: 
##EQU1## 
A difference or magnification deviation z between the predetermined 
magnification (set magnification) m and the actual magnification m' is 
then given by: 
EQU z=(m'/m-1).times.100(%) 
This is illustrated in FIG. 2. As is known therefrom, the magnification 
deviation is considerably large at some set magnifications m. 
Means for correcting the magnification deviation is disclosed, for example, 
in Japanese Patent Application Laid-Open Nos. 4-348334, 61-80140 and 
61-172134. 
In the structure of Japanese Patent Application Laid-Open No. 4-348334, the 
variable power recording is performed by moving a fixed-focus projection 
lens and a variable power mirror for changing an optical path length by 
respective driving means. In this structure, fluctuation of the focal 
length of the projection lens is considered, and the factual focal length 
of the projection lens is measured. On the basis of the measured result, 
corrected positions of the projection lens and the variable power mirror 
are determined. At the time of varying the magnification, displacement 
positions of the projection lens and the variable power mirror are 
corrected. 
In the structure of Japanese Patent Application Laid-Open No. 4-348334, 
however, separate driving systems for driving the projection lens and the 
optical-path-length varying means are individually needed, and hence, 
problems, such as an increase in size of the entire apparatus, an increase 
in cost and an increase in weight of the apparatus, newly occur. 
Further, in the structure of Japanese Patent Application Laid-Open No. 
4-348334, the factual focal length of the projection lens needs to be 
measured, and thus adjustment operation therefor is burdensome. 
In the structure of Japanese Patent Application Laid-Open No. 61-80140, a 
swinging cam having a specific shape is used, and a fixed-focus projection 
lens and a variable power mirror for varying an optical path length are 
moved in an interlocking manner to perform the variable power recording. 
Further, tolerance of the focal length of the projection lens is assumed 
to be about .+-.1%, and the tolerance is compensated for by adjusting the 
position and shape of the swinging cam. 
In the structure of Japanese Patent Application Laid-Open No. 61-80140, 
however, the swinging cam of a specific shape is needed, and the 
positional adjustment of the swinging cam is very troublesome. 
Further, in the structure of Japanese Patent Application Laid-Open No. 
61-80140, since the adjustment is performed by the swinging cam only, so 
that a range of fluctuation of the focal length to be corrected is 
limited. 
In the structure of Japanese Patent Application Laid-Open No. 61-172134, a 
cam is used, and a fixed-focus projection lens and a variable power mirror 
for varying an optical path length are moved in an interlocking manner to 
perform the variable power recording. When there is a fluctuation in the 
focal length of the projection lens, the positional posture of the cam is 
adjusted to compensate for the fluctuation. 
In the structure of Japanese Patent Application Laid-Open No. 61-172134, 
however, the focal length of the used projection lens is measured, the 
optical path length is corrected at the time of a one-to-one magnification 
to attain a focused state, and at the same time, the positional posture of 
the cam is adjusted in accordance with the fluctuation of the focal 
length. 
In such an adjustment method, the focal length of the used projection lens 
needs to be measured, and the adjustment operation of the positional 
posture of the cam requires a troublesome work. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an image-forming 
apparatus and a magnification correction method using this apparatus in 
which a predetermined magnification (a set magnification) and an actual 
magnification are made substantially coincident with each other and an 
accuracy of the magnification is improved by using a correction means or a 
correction method for obtaining an appropriate magnification even if a 
focal length of a fixed-focus image-forming lens fluctuates due to errors 
occurring during its manufacturing process. 
According to one aspect of the present invention, there is provided an 
image-forming apparatus which includes an image-forming unit for 
image-forming image information of an original on a record medium, an 
optical-path-length varying unit for varying a distance between an object 
and an image, a driving unit for driving the image-forming unit and the 
optical-path-length varying unit in an interlocking manner such that the 
image information of the original is formed on the record medium at a 
plurality of magnifications, and a control unit for controlling the 
driving unit. In the structure, positions of the image-forming unit and 
the optical-path-length varying unit are adjustable relative to the 
driving unit. 
Specifically, there are preferably further arranged a coupling portion 
between the driving unit and the image-forming unit or the 
optical-path-length varying unit and an indicator for positional 
adjustment therebetween provided on the coupling portion. 
According to another aspect of the present invention, there is provided an 
image-forming apparatus which includes an image-forming unit for 
image-forming image information of an original on a record medium, an 
optical-path-length varying unit for varying a distance between an object 
and an image, a driving unit for driving the image-forming unit and the 
optical-path-length varying unit in an interlocking manner such that the 
image information of the original is formed on the record medium at a 
plurality of magnifications, a detecting unit for detecting a change in a 
relative position between the driving unit and the image-forming unit or 
the optical-path-length varying unit, and a control unit for controlling 
the driving unit on the basis of a detection result of the detecting unit. 
In the structure, positions of the image-forming unit and the 
optical-path-length varying unit are adjustable relative to the driving 
unit. 
According to another aspect of the present invention, there is provided an 
image-forming apparatus which includes an image-forming unit for 
image-forming image information of an original on a record medium, an 
optical-path-length varying unit for varying a distance between an object 
and an image, a driving unit for driving the image-forming unit and the 
optical-path-length varying unit in an interlocking manner such that the 
image information of the original is formed on the record medium at a 
plurality of magnifications, and a control unit for controlling the 
driving unit on the basis of a change in a relative position between the 
driving unit and the image-forming unit or the optical-path-length unit. 
In the structure, positions of the image-forming unit and the 
optical-path-length varying unit are adjustable relative to the driving 
unit. 
According to another aspect of the present invention, there is provided a 
magnification correction method to be performed in an image-forming 
apparatus, which includes a step of driving a fixed-focus image-forming 
unit and an optical-path-length varying unit in an interlocking manner by 
a common driving unit such that image information of an original is formed 
on a record medium at a plurality of magnifications, a step of adjusting 
positions of the image-forming unit and the optical-path length unit 
relative to the driving unit, a step of detecting a change in a relative 
position between the driving unit and the image-forming unit or the 
optical-path-length varying unit, and a step of controlling the driving 
unit on the basis of the change detected in the detecting step. 
According to still another aspect of the present invention, there is 
provided a magnification correction method to be performed in an 
image-forming apparatus, which includes a step of driving a fixed-focus 
image-forming unit and an optical-path-length varying unit in an 
interlocking manner by a common driving unit such that image information 
of an original is formed on a record medium at a plurality of 
magnifications, a step of adjusting positions of the image-forming unit 
and the optical-path length unit relative to the driving unit, and a step 
of controlling the driving unit on the basis of a change in a relative 
position between the driving unit and the image-forming unit or the 
optical-path-length varying unit. 
According to yet another aspect of the present invention, there is provided 
an image-forming apparatus which includes an image-forming unit for 
image-forming image information of an original on a record medium and an 
optical-path-length varying unit for varying a distance between an object 
and an image, and in which positions of the image-forming unit and the 
optical-path-length varying unit are adapted to be changed such that the 
image information of the original is formed on the record-medium at a 
plurality of magnifications. This image-forming apparatus is characterized 
by a driving unit for driving the image-forming unit and the 
optical-path-length varying unit in an interlocking manner, a fine 
adjustment unit for finely adjusting mounted positions of the 
image-forming unit and the optical-path-length varying unit relative to 
the driving unit, along the optical axis, a detecting unit for detecting 
an adjustment amount of the fine adjustment by the fine adjustment unit, 
an input unit for inputting the adjustment amount detected by the 
detecting unit, and a determining unit for determining a drive amount of 
driving by the driving unit on the basis of the adjustment amount input by 
the input unit. 
Specifically, at coupling portions for coupling the image-forming unit and 
the driving unit to each other, a reference indicator in respect of the 
adjustment amount is provided on one of the coupling portions and division 
indicators in respect of the adjustment amount are provided on the other. 
An interval D of the divisions is set as: 
EQU D=f.times.N/M 
f: focal length of the fixed-focus image-forming unit 
N, M: integers (N&lt;M) 
Further, there may be further arranged a position detecting unit for 
detecting a relative position between the image-forming unit and the 
driving unit, and the adjustment amount of the fine adjustment unit may be 
calculated by an operation unit on the basis of the output value from the 
position detecting unit. 
Furthermore, the determining unit determines a corrected drive amount 
x.sub.m ' relative to a predetermined drive amount of the image-forming 
unit at the time of a desired magnification, from the following relation. 
The corrected drive amount of the image-forming unit at a predetermined 
magnification (the drive amount from a one-to-one magnification to a 
magnification of m) is given by: 
EQU x.sub.m '=S.sub.m X.sub.m 
x.sub.m : drive amount from a one-to-one magnification to a magnification 
of m 
##EQU2## 
EQU k=(L+.DELTA.L)/L 
EQU L=2.times.f 
.DELTA.L=difference in relative position between the image-forming unit and 
the driving unit from a design value 
f=focal length of the fixed-focus image-forming unit 
According to yet another aspect of the present invention, there is provided 
a magnification correction method in which, when a magnification is varied 
to a desired magnification by varying positions of an image-forming unit 
for image-forming image information of an original on a record medium and 
an optical-path-length varying unit for varying a distance between an 
object and an image, the image-forming unit and the optical-path-length 
varying unit are respectively driven to positions of a predetermined 
magnification by a driving unit for driving the image-forming unit and the 
optical-path-length varying unit, the positions of the image-forming unit 
and the optical-path-length unit relative to the driving unit are finely 
adjusted by a fine adjustment unit such that the conditions of the 
predetermined magnification and focussing are satisfied, a relative 
adjustment amount between the driving unit and the image-forming unit or 
the optical-path-length unit subsequent to the fine adjustment is detected 
by a detecting unit, and a corrected drive amount relative to a 
predetermined drive amount at the time of a desired magnification is 
determined by a determining unit on the basis of the detected adjustment 
amount. 
Specifically, the determining unit determines the corrected drive amount 
relative to the predetermined drive amount of the image-forming unit at 
the time of a desired magnification, from the following relation. 
The corrected drive amount of the image-forming unit at a predetermined 
magnification (the drive amount from a one-to-one magnification to a 
magnification of m) is given by: 
EQU x.sub.m '=S.sub.m x.sub.m 
x.sub.m : drive amount from a one-to-one magnification to a magnification 
of m 
##EQU3## 
EQU k=(L+.DELTA.L)/L 
EQU L=2.times.f 
.DELTA.L=difference in relative position between the image-forming unit and 
the driving unit from a design value 
f=focal length of the fixed-focus image-forming unit 
According to yet another aspect of the present invention, there is provided 
an image-forming apparatus which includes an image-forming unit for 
image-forming image information of an original on a record medium and an 
optical-path-length varying unit for varying a distance between an object 
and an image, and in which positions of the image-forming unit and the 
optical-path-length varying unit are adapted to be changed such that the 
image information of the original is formed on the record medium at a 
plurality of magnifications. This image-forming apparatus is characterized 
by a driving unit for driving the image-forming unit and the 
optical-path-length varying unit in an interlocking manner to positions of 
a desired magnification, a fine adjustment unit for finely adjusting 
positions of the image-forming unit and the optical-path-length varying 
unit relative to the driving unit, a detecting unit for detecting an 
adjustment amount of the fine adjustment by the fine adjustment unit, an 
input unit for inputting the adjustment amount detected by the detecting 
unit, a determining unit for determining a drive amount of the driving 
unit on the basis of the adjustment amount input by the input unit, and a 
recording unit for recording data of the drive amount determined by the 
determining unit. 
Specifically, at coupling portions for coupling the image-forming unit and 
the driving unit to each other, a reference indicator with respect to the 
adjustment amount is provided on one of the coupling portions and division 
indicators with respect to the adjustment amount are provided on the 
other. An interval D of the divisions is set as: 
EQU D=f.times.N/M 
f: focal length of the fixed-focus image-forming unit 
N, M: integers (N&lt;M) 
Further, the determining unit determines a corrected drive amount relative 
to a predetermined drive amount of the image-forming unit at the time of a 
desired magnification, from the following relation. 
The corrected drive amount of the image-forming unit at a predetermined 
magnification (the drive amount from a one-to-one magnification to a 
magnification of m) is given by: 
EQU x.sub.m '=S.sub.m x.sub.m 
x.sub.m : drive amount from a one-to-one magnification to a magnification 
of m 
##EQU4## 
EQU k=(L+.DELTA.L)/L 
EQU L=2.times.f 
.DELTA.L-difference Zin relative position between the image-forming unit 
and the driving unit from a design value 
f=focal length of the fixed-focus image-forming unit

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of an image-forming apparatus is shown in FIG. 3. In 
FIG. 3, reference numeral 19 denotes a glass plate for supporting an 
original, and the original (not shown) is put on the glass plate 19. 
Reference numeral 15 denotes a first mirror unit or a full-speed mirror 
unit, and the first mirror unit 15 includes a light source or a lamp 15a, 
light condensing means or shell-shaped reflectors 15b, a path-bending 
mirror-15c, etc. Reference numeral 16 denotes a second mirror unit or a 
half-speed mirror unit, and the second mirror unit 16 includes two 
path-bending mirrors 16a and 16b. A ratio between scan speeds of the first 
and second mirror units 15 and 16 is 2:1, and those mirror units 15 and 16 
are moved in a horizontal or sub-scan direction relative to the glass 
plate 19 and scan the entire range of the original. 
Reference numeral 10 denotes a fixed-focus image-forming lens (a variable 
power optical system) which acts as an image-forming means or unit, and 
the lens 10 image-forms image information of the original on a 
photosensitive drum 18, which acts as a record medium, at a predetermined 
magnification. Reference numeral 14 denotes a zoom-mirror unit or an 
optical-path-length varying means for varying the distance between an 
object and an image, and the zoom-mirror unit 14 includes two path-bending 
mirrors 14a and 14b. Reference numeral 17 denotes a path-bending mirror. 
Reference numeral 18 denotes the above-discussed photosensitive drum which 
acts as a record medium or an image carrier, and the drum 18 is rotated in 
a predetermined direction (the sub-scan direction) at a constant speed. 
Reference numeral 40 denotes a driving means or a variable power driving 
system, and the system 40 interlocks the image-forming lens 10 and the 
zoom-mirror unit 14 with each other. When the magnification is to be 
varied, the driving system 40 drives the image-forming lens 10 and the 
zoom-mirror unit 14 to positions corresponding to a desired magnification, 
on the basis of signals supplied from a driver control means (CPU) 2. 
Reference numeral 1 denotes an adjustment-amount input means or input means 
which supplies an adjustment amount of fine adjustment by a fine 
adjustment means. When performing focussing adjustment and magnification 
adjustment, the fine adjustment means finely adjusts the positions of the 
image-forming lens 10 and the zoom-mirror unit 14 relative to the driving 
means 40 such that the predetermined magnification and focussing are 
satisfied. 
The driver control means 2 not only controls the driving means 40, but also 
acts as a determining means for determining a corrected drive amount 
relative to a predetermined drive amount at the time of a desired 
magnification for the driving means 40, on the basis of the adjustment 
amount input from the adjustment-amount input means 1. The corrected drive 
amount is a drive amount for each of the image-forming lens 10 and the 
zoom-mirror unit 14 which is suited for an actual focal length f'. 
In this embodiment, illumination light from the light source 15a is 
condensed by the light-condensing means 15b and illuminates the original 
put on the glass plate 19. The optical path of image information of the 
illuminated original is bent by the path-bending mirrors 15c, 16a and 16b, 
and the image information is image-formed on the photosensitive drum 18, 
through the path-bending mirrors 14a, 14b and 17, by the image-forming 
lens 10. The image of the image information of the original formed on the 
photosensitive drum 18 is transferred to a copying paper using a 
well-known electrophotographic process (not shown). 
When the image information of the original is to be copied at a desired 
magnification in this embodiment, the image-forming lens 10 and the 
zoom-mirror unit 14 are moved to positions corresponding to the desired 
magnification, by the driving means or variable power driving system 40 
which is controlled by the driver control means 2. For example, when the 
magnification is to be changed from a one-to-one magnification to a 
magnification of m, movement amounts x.sub.m and y.sub.m (design values) 
of the image-forming lens 10 and the zoom-mirror unit 14 can be obtained 
by the following manner. 
With a length between principal planes of the image-forming lens 10 and 
defocus characteristics being disregarded, the movement amount x.sub.m of 
the image-forming lens 10 at the time of changing from a one-to-one 
magnification to a magnification of m is given by: 
EQU x.sub.m =f(1/m-1) (1) 
The change amount y.sub.m of the optical path length in this case is 
represented by: 
EQU y.sub.m =f(m+1/m-2)=x.sub.m -f+f.sup.2 /(x.sub.m +f)) (2) 
f: focal length (design value) of the image-forming lens 
m (m&gt;0): image-forming magnification 
The distance between the original surface and the front principal plane of 
the image-forming lens 10 is given by: 
EQU a=f(1/m+1)=2f+x.sub.m (3) 
The distance between the light reception surface and the rear principal 
plane of the image-forming lens 10 is given by: 
EQU b=f(m+1)=2f-x.sub.m +y.sub.m (4) 
The structure of the copying machine of this embodiment is designed such 
that positions of the fixed-focus image-forming lens 10 and the 
zoom-mirror unit 14 on the optical axis are moved by predetermined amounts 
by the driving means in accordance with the above relations (1) and (2) 
when the magnification is a desired value of m. 
FIG. 4 illustrates the variable power optical system of this embodiment. In 
FIG. 4, the same elements as those in FIG. 3 are designated by the same 
numbers. 
In FIG. 4, reference numeral 3 denotes a driving source or a pulse motor, 
reference numerals 4 and 42 respectively denote pulleys, reference numeral 
41 denotes a wire, reference numeral 6 denotes a connecting plate, 
reference numeral 5 denotes an eccentric cam, and reference numeral 12 
denotes a cam follower. Those elements constitute a portion of the driving 
means. In this embodiment, the pulley 4 is rotated by the driving means 3 
and the pulley 42 is rotated by the wire 41 rotated by the pulley 4. The 
eccentric cam 5 is rotated together with the pulley 42, and has a shape 
represented by polar coordinates (r.sub.m, .theta..sub.m) with an axis of 
the rotational axis. 
##EQU5## 
r.sub.0 : constant r.sub.1 : radius of the pulley 42 
The cam follower 12 is in contact with the eccentric cam 5 at a point 122 
of contact, and is constructed such that the contact point 122 is always 
in contact with the eccentric cam 5 when the cam 5 is rotated. For 
example, the cam follower 12 is urged against the eccentric cam 5 by a 
spring force. Further, the cam follower 12 has an elongate hole 121, and 
is fixed to the zoom-mirror unit 14 including mirrors 141 and 142 by a 
lock pin or a set screw 13. 
The connecting plate 6 connects the wire 41 to the image-forming means 10, 
and is fixed to the wire 41. The connecting plate 6 has an elongate hole 
61, and is fixed to a lens unit frame 101 by a set screw 7. Divisions 8 
for indicating the adjustment amount are provided on the connecting plate 
6. The image-forming lens 10 is fixed to the lens unit frame 101, and a 
reference indicator 9 relevant to the adjustment amount is provided on the 
frame 101. 
The above-discussed set screws 7 and 13 constitute a portion of the fine 
adjustment means. The positions of the image-forming lens 10 and the 
zoom-mirror unit 14 can be finely adjusted along the optical axis by 
unscrewing the set screws 7 and 13, respectively. At this time, a 
detecting means (described later) detects the displacement amounts of the 
adjusted image-forming lens 10 and the zoom-mirror unit 14 relative to the 
design values. Thus, the actual focal length f' can be predicted. 
In this embodiment, the division indicators 8 are provided on the 
connecting plate 6, and the reference indicator 9 is provided on the lens 
unit frame 101, as discussed above. An interval D of the divisions is set 
as: 
EQU D=f.times.N/M 
f: focal length of the image-forming means 
N, M: integers (N&lt;M) 
The divisions at the interval D can be known by a ratio k (=f'/f) between 
the actual focal length f' and the design focal length f. 
In this embodiment, the divisions are formed at the intervals of 0.002 f 
(N=2, M=1000). In this case, the distance from the image-forming lens 10 
to the original surface is 2 f at the time of a one-to-one magnification, 
for example. Hence, one division indicates that the actual focal length f' 
is varied by 0.1% in comparison with the design focal length f. 
The division indicators 8 and the reference indicator 9 constitute a 
portion of the detecting means for detecting the adjustment amount of the 
fine adjustment by the fine adjustment means. As discussed above, the 
adjustment amount, by which the fine adjustment means executes the fine 
adjustment, can be detected from the relative relationship between those 
two indicators. 
In this embodiment, when the driving means 40 is driven to a position of a 
one-to-one magnification, the eccentric cam 5 and the connecting plate 6 
are driven to predetermined positions on the basis of signals from the 
driver control means 2 and thus the image-forming lens 10 and the mirror 
unit 14 are driven accordingly. At this time, a center division 81 is the 
division at which the image-forming lens 10 having an exact focal length 
of the design value satisfies conditions of the magnification (in this 
case, one-to-one magnification) and the focussing. 
An adjustment method for varying the magnification of this embodiment will 
be described. 
Initially, the image-forming lens 10 and the mirror unit 14 are 
respectively fixed to the driving means. 
The driving source 3 is then driven by the driver control means 2, and the 
connecting plate 6 and the eccentric cam 12 are moved to the arrangement 
at the time of a one-to-one magnification. Then, the set screws 7 and 13 
are respectively unscrewed and the positions of the image-forming lens 10 
and the zoom-mirror unit 14 are finely adjusted along the optical axis. 
The respective screws 7 and 13 are tightened at places where the 
conditions of magnification and focussing are satisfied. 
Then, a place of the division indicators 8 indicated by the reference 
indicator 9 is read by a CCD camera or the like. For example, when the 
reference indicator 9 indicates a n-th division from the center division 
81, the actual focal length f' is: 
EQU f'=kf 
k-1+n (division n is positive on the right side in FIG. 4) 
Numerals of k and n are indicators for representing the adjustment amount. 
The adjustment-amount input means 1 supplies data corresponding to the 
indicator k or n. In accordance with the input indicator k or n, the 
driver control means (determining means) 2 determines the corrected drive 
amount x.sub.m ' relative to a predetermined drive amount x.sub.m of the 
image-forming lens 10 at the time of a desired magnification of the 
driving means (variable power driving system) 40. 
The corrected drive amount x.sub.m ' is determined or calculated in the 
following manner. 
In this embodiment, for the image-forming lens 10 having a desired focal 
length f', the movement amount of the image-forming lens 10 is corrected 
as: 
EQU x.sub.m '=x.sub.m .times.S 
At this time, the optical-path-length change amount y.sub.m ' is 
automatically determined from the corrected drive amount x.sub.m ', as 
represented by the relation (2), since the driving means 40 is connected 
to the image-forming lens 10 and the zoom-mirror unit 14. Here, the 
relations (5) and (6) become 
EQU a.sub.m '=2f'+x.sub.m ' (5') 
EQU b.sub.m '=2f'-x.sub.m '+y.sub.m ' (6') 
EQU y.sub.m '=(x.sub.m '-f+f.sup.2 /(x.sub.m '+f)) 
Further, from the relation (7), the actual magnification m' is corrected 
as: 
##EQU6## 
EQU S=k (8) 
EQU Since x'=kx=kf(1/m-1) (9), 
the relation (7') becomes 
##EQU7## 
A difference (magnification deviation) z between the desired magnification 
m (set magnification) and the actual magnification m' is given by: 
EQU z=(m'/m-1).times.100(%) 
The magnification deviation is expressed as illustrated in FIG. 5. 
From the comparison between the magnification deviation (after adjusted) 
shown in FIG. 5 and the magnification deviation (not adjusted) shown in 
FIG. 2, it can be known that the magnification deviation can be reduced to 
about a fourth (1/4) in this embodiment. 
There are several methods for determining the corrected drive amount 
x.sub.m ', as follows, 
(1) A memory means (recording means) for recording the indicator k or n is 
provided, and the corrected drive amount x.sub.m ' corresponding to the 
indicator k or n is read from a memory table prepared beforehand, such as 
a ROM, each time needed. 
(2) A memory means for recording the indicator k or n is provided, and the 
corrected drive amount x.sub.m ' corresponding to the indicator k or n is 
calculated each time needed. 
(3) The corrected drive amount x.sub.m ' corresponding to the indicator k 
or n is determined by the determining means (operation unit), such as an 
external jig tool, is recorded in a memory table (recording means such as 
a ROM) arranged in a body, and is read each time needed. 
Conventional means, such as a ROM and a resistance value of a variable 
resistor, can be used as the memory means. In the case of (3), the element 
1 in FIG. 3 is the external determining means (operation unit), and 
information of the drive amount determined by the determining means 1 is 
input into the driver control means (CPU) 2 in the body and recorded in 
the memory means (recording means). Thus, when the determining means is 
provided separately from the apparatus body and used as an assemblage jig 
tool, there is no need to arrange the means for determining the corrected 
drive amount in the apparatus body. Thus, its cost can be reduced. 
In this embodiment, the division indicators 8 and the reference indicator 9 
are respectively provided on the connecting plate 6 and the lens unit 
frame 101, but when those indicators are respectively marked as nicks in 
the connecting plate 6 and the lens unit frame 101, the number of parts 
can be reduced. 
Thus, when the positions of the image-forming lens 10 and the zoom-mirror 
unit 14 are changed along the optical axis as discussed above to vary the 
magnification to a desired value, the positions of the image-forming lens 
10 and the zoom-mirror unit 14 on the optical axis are finely adjusted by 
the fine adjustment means to satisfy a predetermined magnification and the 
focussing and the relative adjustment amount between the driving means 40 
and the image-forming lens 10 or the zoom-mirror unit 14 subsequent to the 
fine adjustment is detected by the detecting means. The thus-detected 
adjustment amount is input into the input means 1, and the determining 
means 2 determines the drive amount (corrected drive amount) x.sub.m ' of 
the driving means 40 on the basis of the thus-input adjustment amount. The 
correction is made by moving the positions of the image-forming lens 10 
and the zoom-mirror unit 14 on the basis of the determined information 
such that the predetermined magnification (set magnification) 
approximately coincides with the actual magnification. Accordingly, an 
appropriately focused image can be obtained even when the focal length of 
the image-forming lens 10 fluctuates due to errors during the 
manufacturing process. 
A second embodiment of the present invention will be described. In the 
second embodiment, as the means for determining the corrected drive amount 
x.sub.m ', the following relations are substituted into the relation (7') 
explained in the first embodiment: 
EQU m'=m (10) 
EQU f'=kf 
EQU x'=Sx=S.multidot.f(1/m-1) 
Thus, 
##EQU8## 
(2k-1)(S(1-m)+m=2km+S(1-m)+m!(2k-1)(1-m)s+2km=(1-m.sup.2 S.sup.2 
+(2k+1)m(1-m)S+2km.sup.2 
(1-m.sup.2 S.sup.2 +2k(m-1)+(m+1)!.multidot.(1-m)S+2km(m-1)=0 
(1-m)S.sup.2 +2k(m-1)+(m+1)!S'-2km=0 
##EQU9## 
(m.noteq.1) (because S&lt;0) 
By using this S, the corrected drive amount x.sub.m ' is obtained as: 
EQU x'=x.sub.m .times.S 
x.sub.m : drive amount from a one-to-one magnification to a magnification 
of m 
EQU k=(L+.DELTA.L)/L 
EQU L=2.times.f 
.DELTA.L=difference in relative position between the image-forming lens and 
the driving means from a design value 
f=focal length of the image-forming lens 
Hence, the actual magnification m' becomes equal to the desired 
magnification (set magnification) m, as expressed in the relation (10). 
Thus, still more accurate correction can be made in the second embodiment, 
compared with the first embodiment. 
FIG. 6 illustrates coupling portions of a third embodiment of the present 
invention. The third embodiment is different from the first embodiment 
(FIG. 4) in that a reference indicator 49 is marked on the connecting 
plate 6 while division indicators 48 are marked on the frame 101. Other 
structure and optical operation of the third embodiment are substantially 
the same as those of the first embodiment, and thus the same effects are 
obtained. 
Specifically, the divisions 48 are notched at a pitch of P mm/division in 
this embodiment. In this case, when the reference indicator 49 indicates a 
division of n' (the division of n' is positive on the left side in FIG. 
6), the reduction is executed as follows: 
EQU n=n'P/2f or k=2f+n'P/2f 
Thus, S is calculated by the above-discussed calculation method. 
FIG. 7 illustrates a main portion of a fourth embodiment of the present 
invention. In FIG. 7, the same elements as those in FIG. 4 are designated 
by the same numbers. 
The fourth embodiment is different from the first embodiment (FIG. 4) in 
that a reference indicator 59 is marked on the zoom-mirror unit 14 while 
division indicators 58 are marked on the cam follower 12. The division 
pitch P, other structure and optical operation of the fourth embodiment 
are substantially the same as those of the first embodiment, and thus the 
same effects are obtained. 
More particularly, as is known from the relations (3) and (4), where the 
focal length f at the time of design is changed to the actual focal length 
f' (f.fwdarw.f'), fine adjustment amounts xA and yA of the image-forming 
lens and the zoom-mirror unit at the time of a magnification of m=1 are 
respectively given by: 
EQU xA=2(f'-f) 
EQU yA=2(f'-f) 
Thus, those values are equal. Therefore, even when the reference indicator 
59 is provided on the zoom-mirror unit 14 and the division indicators 58 
are put on the cam follower 12, this embodiment can be treated 
equivalently to the first embodiment. 
Even when the reference indicator 59 is notched on the cam follower 12 and 
the division indicators 58 are notched on the zoom-mirror unit 14, the 
present invention can also be applied, similar to the fourth embodiment. 
FIG. 8 illustrates a main portion of a fifth embodiment of the present 
invention. In FIG. 8, the same elements as those in FIG. 4 are designated 
by the same numbers. 
The fifth embodiment is different from the first embodiment (FIG. 4) in 
that in place of the reference indicator and the division indicators, 
there are arranged a linear sensor 19 for detecting the displacement 
amount of a flag plate 62 attached to the connecting plate 6 and an 
operation circuit (operation means) 20 for calculating the adjustment 
amount of the fine adjustment means from the output value of the linear 
sensor 19. Other structure and optical operation of the fifth embodiment 
are substantially the same as those of the first embodiment, and thus the 
same effects are obtained. 
The flag plate 62 and the linear sensor 19 constitute a portion of a 
position detecting means, and detect a change in the relative position 
between the image-forming lens 10 and the driving means. Namely, the 
displacement amount of the image-forming lens 10 relative to the driving 
means is detected. The operational means 20 calculates the adjustment 
amount of the fine adjustment means on the basis of the output value of 
the position detecting means. 
An adjustment method for varying the magnification of this embodiment will 
be described. 
Initially, the image-forming lens 10 and the mirror unit 14 are 
respectively fixed to the driving means. 
The driving source 3 is then driven by the driver control means 2, and the 
connecting plate 6 and the eccentric cam 12 are moved to the arrangement 
at the time of a one-to-one magnification. Then, the set screws 7 and 13 
are respectively unscrewed and the positions of the image-forming lens 10 
and the zoom-mirror unit 14 are finely adjusted along the optical axis. 
The respective screws 7 and 13 are tightened at places where the 
conditions of magnification and focussing are satisfied. 
Then, the position of the flag plate 62 is detected by the linear sensor 
19. The detection value detected by the linear sensor 19 is converted into 
the adjustment amount k by the operation circuit 20. For this purpose, a 
data table of the detection value and the adjustment amount k is produced 
in the operation circuit 20 beforehand, and those are corresponded to each 
other. 
Then, the corrected drive amount x.sub.m ' of the image-forming lens is 
determined from the adjustment amount k, by the same calculating method as 
that of the first or second embodiment. Thus, the same effects as those of 
the above-discussed embodiments can be obtained. 
The position detecting means of this embodiment can automatically detect 
the actual focal length f'. Therefore, when adjustments of focussing and 
magnification are performed at a predetermined magnification, corrections 
at other magnifications can be automatically achieved. 
Further, FIG. 8 illustrates an example in which the displacement amount of 
the image-forming lens is detected by the linear sensor, but the same 
effects can also be obtained by detecting the displacement amount of the 
mirror unit as illustrated in FIG. 9. 
As described in the foregoing, in an image-forming apparatus and a 
magnification correction method using this apparatus according to the 
present invention, correcting means and method are used to obtain a proper 
magnification even if the focal length of an image-forming lens fluctuates 
due to errors occurring during the manufacturing process. Therefore, the 
following effects or technical advantages can be attained. 
(1) Adjustment of the magnification can be readily performed, and 
magnification accuracy is improved. 
(2) Assemblage efficiency is improved. 
(3) No complex input structure is needed, so that the number of parts can 
be reduced and the structure can be compact in size. 
(4) A driving source can be reduced, so that the entire structure can be 
small in size, cost thereof can be reduced and noises thereof can be 
lowered.