JPH08313800A - Image forming device provided with focus detecting means - Google Patents

Abstract

PURPOSE: To provide an image forming device provided with a focus detecting means accurately and quickly performing the focusing of a projected image formed on a screen surface or on a recording medium surface and easily obtaining an excellent projected image. CONSTITUTION: In the case the projected image 6 illuminated by an illumination means LX is projected on a projection surface by a projection lens 7, a luminous flux separation means 15 is provided on the exit side of the projection lens 7; and an image-formation lens 16, a pair of image reformation lenses 19a and 19b dividing the pupil of the lens 7 into two areas and respectively forming secondary projected images from the luminous fluxes passing through two divided pupil areas, and a photodetector means constituted of a pair of line sensors 20a and 20b near the image surface of the lenses 19a and 19b are provided on the reflection side of the separation means 15. Then, the device has measuring means 28a and 28b measuring the light quantity of the luminous fluxes passing through two divided pupil areas in the case of detecting the focusing state on the projection surface of the lens 7 by detecting the relative positional relation of the distribution of light quantity concerning two secondary projected images by the photodetector means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a focus detecting means, and more particularly to an image forming state of a projected image projected on a screen surface or a recording medium surface by a projection lens. The present invention relates to an image forming apparatus having a focus detection unit that is suitable for an apparatus such as a microfilm reader or a microfilm reader printer that can detect and obtain a good projected image that is always in focus.

[0002]

2. Description of the Related Art An image forming apparatus such as a general microfilm reader printer has a reader section (observation system) for enlarging and projecting a projection image (image information) of a microfilm, etc., which is reduced and recorded, onto a screen surface by a projection lens. And a printer unit (recording system) for projecting and recording the projected image on a photoconductor by a projection lens and outputting the image as a copy.

In many microfilm reader printers, the projection lens is manually moved in the optical axis direction to obtain a focused projection image on the screen surface or the photoconductor surface.

Since such an operation is performed, focus adjustment is troublesome, and recently, a reader printer capable of automatically focusing in a short time by using a focus detecting means has been desired.

In general, when a projection lens having a high projection magnification of 40 to 50 is used in an image forming apparatus, the depth of focus becomes as shallow as 0.02 mm. Therefore, in order to form a clear projected image on the screen surface or the photosensitive drum surface, the focus detection means is required to have high optical accuracy.

An image forming apparatus using the focus detecting means is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-316838 or 63-7.
Various proposals have been made in Japanese Patent Publication No. 0813.

In Japanese Patent Laid-Open No. 63-316838, a reader system optical path for projecting a magnified image and a focus detecting optical path for guiding a light beam to a focus detecting light receiving element are provided. The next image forming lens is arranged to reduce the image projected by the projection lens to form an image on the light receiving element. Then, the focus is adjusted using the signal obtained from the light receiving element.

In Japanese Patent Laid-Open No. 63-70813, an image sensor is provided to read a projected image, and a contrast signal for the projected image is obtained for each of a plurality of regions of the image sensor. The position of the lens on the optical axis is obtained as the focus position for each area. Then, the focus adjustment is performed by determining the focus position of the projection lens by using a set of focus positions that include the largest focus position among the focus positions of each area and are close to each other.

[0009]

In the image forming apparatus having these conventional focus detection means, for example, when the projection image such as a microfilm is exchanged, or when the projection lens is exchanged with a lens having a different magnification, the screen surface is changed. When the image formation state of the projected image is deviated on the upper side (or on the surface of the photosensitive drum), the focus adjustment is performed while moving the projection lens on the optical axis.

In this case, it suffices to adjust the focus only once, but if not, it is necessary to move the projection lens in the front-back direction on the optical axis while observing the projected image on the screen surface to adjust the focus. Therefore, there is a problem that the observer feels troublesome because the subject is in focus or out of focus.

Therefore, in the conventional image forming apparatus having the focus detecting means, the applicant of the present invention has previously proposed JP-A-6-5.
As described in Japanese Patent No. 9183, either one of an image forming lens for focus detection forming a focus detecting unit or a focus detecting unit including a line sensor is moved on the optical axis to obtain the amount of movement of the projection lens to the in-focus point. After that, by moving the projection lens on the optical axis to adjust the focus of the projected image,
Focusing can be performed at one time while observing the projected image on the screen surface, so that the focus can be adjusted accurately without bothering the observer.

In the publication, the image shift (pupil division) method is used as the focus detection method. In the case of focus detection using this image shift method, for example, in order to accurately detect the focus state of the projection lens without erroneous recognition, the light amount distributions of the two projection images formed on the pair of line sensor surfaces are They must have the same condition. For example, if there are variations in the amount of illumination light of the illumination system, there is a problem that the influence must be removed.

In order to solve the above problems, the present invention is to detect the image formation state of a projection image projected on a screen surface or a recording medium surface by a projection lens by focus detection means using an image shift method. , The pupil of the projection lens is divided into two regions, the light quantity of the light flux passing through the divided two pupil regions is measured by the measuring means, and further, by the correcting means based on the output signal from the measuring means. By correcting the sensitivities of the pair of line sensors as the light receiving means, it is possible to correct variations in the amount of illumination light of the illumination system and to form an image having a focus detection means capable of performing proper focus detection without erroneous recognition. The equipment is provided.

[0014]

An image forming apparatus having a focus detecting means of the present invention comprises (1-1) a projection image illuminated by an illumination means on a projection surface such as a screen surface or a recording medium surface by a projection lens. When projecting onto a projection lens, a light beam separating means for reflecting a part of an incident light beam is provided on the exit side of the projection lens, and an imaging lens and a pupil of the projection lens are divided into two regions on the reflection side of the light beam separating means. 2 from the light fluxes passing through the two divided pupil areas.
A pair of re-imaging lenses that form the next projection image and a light receiving unit composed of a pair of line sensors are provided in the vicinity of the image plane of the pair of re-imaging lenses, and the two light receiving units are provided by the light receiving unit. What is claimed is: 1. An image forming apparatus, comprising: focus detecting means for detecting a relative position of a light quantity distribution with respect to a projected image to detect a focus state on a projection surface of the projection lens. It is characterized in that it has a measuring means for measuring the light quantity of the light flux passing through the two pupil regions.

In particular, the luminous flux separating means is composed of a half mirror, and the measuring means is a pair of photometric elements corresponding to the pair of line sensors and provided on the back surface of the half mirror. The measuring means corresponds to the pair of line sensors and is a parallel flat glass having a pair of photometric elements on at least one plane provided in the vicinity of the imaging lens, and the measuring means is the light receiving element. The image forming lens is constituted by the light receiving means when moved on the optical axis so that the focus of the secondary projection image formed on the surface is largely deviated, and the measuring means is arranged on the light receiving means surface. It is characterized in that it is constituted by the light receiving means when an optical member having an arbitrary refracting power is removably inserted into the optical path so that the formed secondary projection image is largely out of focus.

(1-2) When the projection image illuminated by the illuminating means is projected on the projection surface such as the screen surface or the recording medium surface by the projection lens, a part of the incident light flux is reflected on the exit side of the projection lens. A light beam separating means is provided, and an imaging lens and a pupil of the projection lens are provided on the reflection side of the light beam separating means.
And a pair of re-imaging lenses each of which forms a secondary projection image from a light beam passing through two divided pupil regions, and a pair of re-imaging lenses near the image plane. When a light receiving means including a line sensor is provided and the light receiving means detects the relative positional relationship of the light amount distributions of the two secondary projection images, the focus state on the projection surface of the projection lens is detected, The light quantity of the light flux passing through the two divided pupil regions is measured by the measuring means, and the sensitivity of the pair of line sensors is corrected by the correcting means based on the output signal from the measuring means. It has a feature.

In particular, the luminous flux separating means is composed of a half mirror, and the measuring means is a pair of photometric elements corresponding to the pair of line sensors and provided on the back surface of the half mirror. The measuring means corresponds to the pair of line sensors and is a parallel flat glass having a pair of photometric elements on at least one plane provided in the vicinity of the imaging lens, and the measuring means is the light receiving element. The image forming lens is constituted by the light receiving means when moved on the optical axis so that the focus of the secondary projection image formed on the surface is largely deviated, and the measuring means is arranged on the light receiving means surface. It is characterized in that it is constituted by the light receiving means when an optical member having an arbitrary refracting power is removably inserted into the optical path so that the formed secondary projection image is largely out of focus.

[0018]

EXAMPLE 1 FIG. 1 is a schematic view of a main part of an optical system of Example 1 of the present invention. FIG. 2 is an enlarged explanatory view in which a part of FIG. 1 is enlarged.

In the figure, reference numeral 1 is a light source means, which comprises, for example, a halogen lamp or a fluorescent lamp. Reference numeral 2 denotes a condenser lens which collects the light flux from the light source means 1.
Reference numeral 3 is a heat insulating glass, and 4 is a cold mirror. The optical members 3 and 4 remove the infrared light component from the light flux emitted from the light source means 1 to suppress the temperature rise on the projected image 6 surface. There is. 5 is a field lens. In this embodiment, the illumination means (illumination system) LX is composed of the elements denoted by reference numerals 1, 2, 3, 4, and 5.

Reference numeral 6 denotes a transmission type projection image (image information), which is made of, for example, a microfilm. Reference numeral 7 denotes a projection lens, which magnifies and projects the projection image 6 on the screen 10 surface or the photosensitive drum (recording medium) 14 surface.

The projection lens 7 is a focus detecting means 10 which will be described later.
Based on the signal (output value) obtained in step 1, the driving means 27 controls the movement of the projected image on the optical axis of the screen 10 as shown by the arrow 7a, thereby adjusting the focus of the projected image on the screen 10.

Reference numeral 15 denotes a light beam separating means, which is composed of a half mirror and is provided in the optical path on the exit side of the projection lens 7 between the projection lens 7 and the screen 10 surface. Part of the light flux is separated.

The half mirror 15 in this embodiment has a pair of photometric elements (a-
SPD) 28a and 28b are provided by vapor deposition. Then, as will be described later, the light amount of the light flux passing through the two pupil regions of the projection lens 7 divided by the focus detection unit 100 is measured by the pair of photometric elements 28a and 28b, and the measured photometric value is measured by the light amount measuring circuit. It is digitized by 29. The pair of photometric elements 28a and 28b of the measuring means 28 are provided in correspondence with the pair of line sensors (two light receiving element rows) 20a and 20b for focus detection as the light receiving means. Then, based on the output signal from the light quantity measurement circuit 29, the CCD sensitivity correction circuit 30 as a correction means makes the light quantity distributions of the two projected images formed on the surfaces of the pair of line sensors 20a and 20b identical. The pair of line sensors 2
The sensitivities of 0a and 20b are corrected.

Reference numeral 16 is an imaging lens (reduction lens) for focus detection. Reference numeral 17 denotes a distance measuring field mask for focus detection, which is provided in the vicinity of the planned image forming plane P of the image forming lens 16.
The amount of light incident on the pair of line sensors 20a and 20b is limited.

Reference numeral 18 denotes a field lens having a positive refractive power for focus detection, which is a planned image forming plane P of the image forming lens 16.
It is provided in the rear of the vicinity. In this embodiment, the pupil of the pair of re-imaging lenses 19a and 19b for focus detection as the re-imaging system (secondary imaging lens system) and the exit pupil of the projection lens 7 are substantially conjugate with each other by the field lens 18. And the exit pupil of the projection lens 7 is divided into two regions.

The pair of re-imaging lenses 19a and 19b are arranged symmetrically with respect to the optical axis, and the pair of line sensors 2
0a and 20b are arranged symmetrically with respect to the optical axis corresponding to the pair of re-imaging lenses 19a and 19b.

In the present embodiment, reference numerals 17, 18,
Each of the elements 19 and 20 constitutes the focus detection unit 100, and the half mirror 15, the imaging lens 16 and the focus detection unit 100 constitute the focus detection means 101. The focus detection method of this embodiment uses a so-called known image shift method.

Reference numeral 21 denotes an encoder, which forms an imaging lens 16
Is provided corresponding to the position on the optical axis of the imaging lens 16. A photo interrupter 22 has a light emitting element 22a and a light receiving element 22b,
The movement amount of the imaging lens 16 is detected by using the encoder 21.

A focal position detection circuit 24 detects the focus state of the projection lens 7 by using the output signals from the pair of line sensors 20a and 20b. A movement amount calculation circuit 25 calculates the movement amount of the projection lens 7 on the optical axis using the output signal from the focus position detection circuit 24 and the data from the ROM 23 in which the magnification information of the projection lens 7 is stored. are doing. A motor drive circuit 26 moves the projection lens 7 on the optical axis via a drive motor 27 based on a signal from the movement amount calculation circuit 25.

Reference numeral 102 denotes a movable print scanning unit, which has a scanning mirror 11 and a reflection mirror 12, and moves so as to be positioned in the optical path during printing as indicated by an arrow A in the drawing, and during a reader. Evacuated outside the optical path. Reference numeral 13 is a slit for printing, which limits the amount of light exposed on the surface of the photosensitive drum 14. Reference numeral 14 is a photosensitive drum as a recording medium.

Reference numeral 8 is a reflection mirror for the reader, and 9 is a rotatable rotation mirror for the reader, which is rotated to the position 9a for the reader and to the position 9b for printing as shown by arrow B.

In this embodiment, the luminous flux emitted from the light source means 1 is condensed by the condenser lens 2, passes through the heat insulating glass 3 and is reflected by the cold mirror 4, and then the projected image 6 of the projected image 6 is transmitted through the field lens 5. Illuminates the effective illumination area. The light flux based on the projection image 6 that has passed through the projection lens 7 is directed by the half mirror 15 to the screen 10 surface side (and the photosensitive drum 14 surface) and the focus detection unit 1.
It is separated into two directions, the 00 direction.

In this embodiment, each element is set so that the light beam from the light source means 1 is focused (imaged) in the vicinity of the entrance pupil position of the projection lens 7, that is, Koehler illumination is performed.

Then, at the time of a reader for observing the projected image 6 on the screen 10 surface, the luminous flux transmitted through the half mirror 15 is guided to the screen 10 surface via the reflection mirror 8 and the rotating mirror 9, and onto the surface. It forms an enlarged projection image.

Further, when the printer forms a projection image on the surface of the photosensitive drum 14, the scanning unit 10 for the printer is used.
2 is moved so as to be positioned in the optical path as shown by an arrow A in the figure, and the light flux transmitted through the half mirror 15 is reflected by the scanning mirror 11 and the reflection mirror 12 and is incident on the surface of the photosensitive drum 14. Then, an enlarged projection image is formed on the surface of the photosensitive drum 14.

At this time, the scanning mirror 11 and the reflection mirror 1
2 is moved integrally to scan the surface of the photosensitive drum 14 in the sub-scanning direction, whereby the image information of the entire projected image 6 is projected and recorded on the surface of the photosensitive drum 14.

On the other hand, the light flux based on the projection image reflected by the half mirror 15 is imaged by the imaging lens 16 on the distance measuring field mask (planned imaging surface) 17, and the projected image thus formed is passed through the field lens 18 to Pair of re-imaging lenses 19
A pair of line sensors 20a, 20b by a, 19b
It is projected on the surface.

That is, in the present embodiment, the projection image formed in the vicinity of the distance measuring field mask 17 is formed by a pair of re-imaging lenses 19a, 1a.
9b forms two projected images (light amount distribution) on the surface of the pair of line sensors 20a and 20b.

At this time, the pair of line sensors 20a, 2
The light quantity of the light flux passing through each pupil region of the projection lens 7 divided as described later so that the light quantity distributions of the two projection images formed on the 0b plane are identical to each other is measured by the measuring means, and the measurement is performed. Based on the result, the correction means corrects the sensitivities of the pair of line sensors 20a and 20b. Then, the focus state of the projection lens 7 is detected by obtaining the relative positional relationship between the two light amount distributions by the focus position detection circuit 24.

Further, in this embodiment, at this time, the image forming lens 16 is moved along the optical axis as indicated by an arrow D in the figure, and the moving amount of the projection lens 7 up to the focal point is coupled to the image forming lens 16. Read through the photo interrupter 22 and send the data to the movement amount calculation circuit 25,
The signal from the focus position detection circuit 24 and the projection lens 7
Using the data and the like from the ROM 23 that stores the magnification information and the like of the projection lens 7
To find the amount of movement on the optical axis. Then, based on the signal from the movement amount calculation circuit 25, the motor drive circuit 26 moves the projection lens 7 in the direction of the arrow 7a on the optical axis via the drive motor 27.

As described above, in this embodiment, the amount of movement of the projection lens 7 is obtained in advance by the movement amount calculation circuit 25, and focus adjustment is not performed while moving the projection lens 7 several times along the optical axis. The focus can be adjusted with a single movement. As a result, the focus adjustment can be performed without giving the observer a trouble.

In this embodiment, after the focus adjustment is completed, the half mirror 15 as the light beam separating means may be rotated as shown by an arrow C in the figure so as to be located outside the optical path, whereby the screen 10 surface is displayed. Illumination and photosensitive drum 14 on
It is possible to prevent the amount of exposure on the surface from decreasing.

Next, a method for correcting the sensitivities of the pair of line sensors based on the output signal from the measuring means when performing focus detection will be described with reference to FIG.

The focus detecting means 101 in the present embodiment uses the light fluxes that have passed through different areas of the pupil of the projection lens 7 by the re-imaging system 19 to further select a plurality of projection images formed in the vicinity of the planned imaging plane P. The in-focus state of the projection lens 7 is detected by forming a projection image and determining the relative positional relationship of the light amount distributions of the plurality of projection images by the pair of line sensors 20a and 20b.

That is, it is determined whether or not it is in focus depending on whether or not the light amount distributions of a plurality of projection images are the same.
Therefore, even if the light quantity distributions are similar, they are not considered to be the same. Therefore, for example, the light distribution characteristics of a light source such as a fluorescent lamp or a halogen lamp are asymmetrical due to manufacturing errors or the like,
Alternatively, when the mounting position of the light source is deviated due to mounting error or the like, even if the light amount distributions of the two projected images formed on the pair of line sensors 20a and 20b are in focus, It may not be the same.

Therefore, in this embodiment, a pair of line sensors 20a and 20b are formed on the rear surface 15a of the half mirror 15 as described above so that the light amount distributions of the two projected images formed on the surfaces are the same. The output signals from the photometric elements 28a and 28b are measured by the light amount measuring circuit 29, and the sensitivity of the pair of line sensors 20a and 20b is corrected by the CCD sensitivity correction circuit 30 based on the signal from the light amount measuring circuit 29. . This allows accurate focus detection without erroneous recognition.

FIG. 3 is an explanatory view showing a vapor deposition shape of a pair of photometric elements vapor-deposited on the back surface of the half mirror, and FIG. 4 is a main part configuration diagram showing the configuration of the photometric elements. 3 and 4, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

As shown in FIG. 4, the photometric device in this embodiment has transparent electrodes 52a, as on the surface of the glass 51 of the base.
i (amorphous silicon) 52b and an opaque electrode 52c are sequentially stacked. Therefore, a pair of photometric elements 28a, 2a is formed on the entire back surface 15a of the half mirror 15.
When 8b is vapor-deposited, there arises a problem that the projected image cannot be observed on the screen. Therefore, in this embodiment, as shown in FIG. 3, the pair of photometric elements 28a and 28b are formed in a lattice shape so as not to interfere with the optical function of the half mirror 15.

As described above, in the present embodiment, as described above, the light amount of each pupil light flux transmitted through the half mirror 15 is provided to the half mirror 15 on the back surface 15a of the pair of photometric elements 28.
a, 28b, the measured photometric value is digitized by the light amount measuring circuit 29, and the CCD sensitivity correction circuit 30 calculates the light amount distribution of the two projected images formed on the pair of line sensors 20a, 20b. The sensitivities of the pair of line sensors 20a and 20b are corrected so as to be the same. With this, it is possible to prevent erroneous recognition as out-of-focus from the detection result that the light amount distributions of the projected images formed on the pair of line sensors 20a and 20b are different from each other even if they are in focus.

FIG. 5 is a schematic view of the essential portions of Embodiment 2 around the focus detection means of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

The present embodiment is different from the above-mentioned first embodiment only in the structure of the measuring means, and the other structure and the optical action are substantially the same as those in the above-mentioned first embodiment, whereby the same effect is obtained. Is getting

That is, the measuring means in the present embodiment is the imaging lens 16 between the half mirror 15 and the imaging lens 16.
A flat surface 31a on the side of the imaging lens 16 provided in a nearby optical path
The focus detection unit 1 comprises a parallel flat glass 31 on which a pair of photometric elements (a-SPD) 32a and 32b corresponding to the pair of line sensors 20a and 20b are vapor-deposited.
The light quantity of the light flux passing through the two pupil regions of the projection lens 7 divided by 00 is measured. The photometric value measured by the pair of photometric elements 32a and 32b is used as the light amount measuring circuit 2
9 so that the light amount distributions of the two projected images formed on the surfaces of the pair of line sensors 20a and 20b by the CCD sensitivity correction circuit 30 based on the output signal from the light amount measuring circuit 29 become the same. Further, the sensitivities of the pair of line sensors 20a and 20b are corrected. As a result, accurate focus detection without erroneous recognition is performed as in the first embodiment.

Further, a pair of photometric elements 32 in this embodiment.
a and 32b are half mirrors 15 as compared with the first embodiment.
Since the light amount of the light flux which has passed through each pupil region reflected by is received in the direction perpendicular to the optical axis, the pair of photometric elements 32
There is an advantage that the light receiving surfaces of a and 32b can be made small.
The parallel flat glass 31 is a pair of line sensors 20a,
After the sensitivity of 20b is corrected, it may be configured to be retracted out of the optical path.

FIG. 6 is a schematic view of the essential portions of the third embodiment around the focus detection means of the present invention. In the figure, the same elements as those shown in FIG. 1 are designated by the same reference numerals.

The present embodiment is different from the above-mentioned first embodiment only in the structure of the measuring means, and the other structure and the optical action are substantially the same as those in the above-mentioned first embodiment. It has an effect.

That is, in this embodiment, an adapter lens (optical member) 33 having a positive refractive power that can be inserted and removed before focus detection is inserted into the optical path in the vicinity of the imaging lens 16 so that the focus detection system operates. The focus is largely removed, and the light flux of the microfilm 6 in a wide image range is a pair of line sensors 20.
It is possible to project the images on a and 20b on average. In this embodiment, the pair of line sensors 20a, 2 at this time
0b as a measuring means, and the pair of line sensors 20a,
The light quantity of the light flux passing through the two pupil areas of the projection lens 7 divided by the focus detection unit 100 is measured using the output signal obtained from 20b, and is quantified by the light quantity measuring circuit 29. Then, based on the output signal from the light quantity measuring circuit 29, the CCD sensitivity correction circuit 30 sets the pair of line sensors 20a and 20b so that the light quantity distributions of the two projected images formed on the surfaces of the pair of line sensors 20a and 20b are the same. The sensitivity of the line sensors 20a and 20b is corrected. afterwards,
Focus is detected by retracting the adapter lens 33 out of the optical path. The purpose of unfocusing is to eliminate the influence of the image.

In this embodiment, the adapter lens 3 which can be inserted and removed is used as a means for defocusing the focus detection system.
Although the third embodiment is used, the present invention can be applied similarly to the first embodiment described above even if the imaging lens 16 is moved on the optical axis without using the adapter lens 33 to largely defocus. be able to.

Further, the measuring means is not limited to the means shown in each of the embodiments, and any means can be used as long as the light quantity of the light flux passing through the two pupil regions of the projection lens divided as described above can be measured. The present invention can be applied to the same means as the above-mentioned embodiments even by means.

[0059]

As described above, according to the present invention, when the image forming state of the projection image projected on the screen surface or the recording medium surface by the projection lens is detected by the focus detecting means using the image shift method. , The pupil of the projection lens is divided into two regions, the light amount of the light flux passing through the divided two pupil regions is measured by the measuring means, and the light receiving means is based on the output signal obtained by the measuring means. By correcting the sensitivities of the pair of line sensors by means of the correction means, even if an asymmetry of the orientation characteristics of the light source or a mounting error of the light source occurs, it is possible to always perform proper focus detection without misrecognition. An image forming apparatus having a detecting means can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part of an optical system according to a first embodiment of the present invention.

FIG. 2 is an enlarged explanatory view of a part of FIG.

FIG. 3 is an explanatory view showing the shape of the photometric element shown in FIG.

FIG. 4 is an explanatory diagram showing a configuration of a photometric element.

FIG. 5 is a schematic view of a main part of a main part of a second embodiment of the present invention.

FIG. 6 is a schematic view of a main part of a main part of a third embodiment of the present invention.

[Explanation of symbols]

 LX Illuminating means 1 Light source means 2 Condenser lens 3 Insulating glass 4 Cold mirror 5 Field lens 6 Projection image 7 Projection lens 15 Light flux separating means 16 Imaging lens 17 Distance measuring field mask 18 Field lens 19 Re-imaging system 19a, 19b Recombining Image lens 20 Light receiving means 20a, 20b Light receiving element (line sensor) 8, 12 Reflecting mirror 9 Rotating mirror 10 Screen 11 Scanning mirror 13 Slit 14 Recording medium (photosensitive drum) 28 ROM 24 Focus position detection circuit 25 Movement amount calculation circuit 26 motor drive circuit 27 drive motors 28a, 28b photometric element 29 light quantity measurement circuit 30 CCD sensitivity correction circuit 31 parallel flat glass 32a, 32b photometric element 33 adapter lens 100 focus detection unit 101 focus detection unit 102 scanning unit

Claims (12)

[Claims] 1. A light beam separation means for reflecting a part of an incident light beam on the exit side of the projection lens when the projection image illuminated by the illumination means is projected by a projection lens onto a projection surface such as a screen surface or a recording medium surface. Is provided on the reflection side of the light beam separating means, and the pupil of the projection lens is divided into two regions, and a pair of secondary projection images are formed from the light beams passing through the two divided pupil regions. Re-imaging lens and a pair of light-receiving means composed of a pair of line sensors in the vicinity of the image plane of the pair of re-imaging lenses, the light-receiving means providing relative light amount distributions of the two secondary projection images. An image forming apparatus having focus detection means for detecting a focus state on a projection surface of the projection lens by detecting a positional relationship, wherein the image forming apparatus is a light flux passing through the two divided pupil regions. Measuring the amount of light Image forming apparatus having a focus detecting means, characterized in that it has a stage. 2. The image forming apparatus having the focus detecting means according to claim 1, wherein the light beam separating means comprises a half mirror. 3. The focus detecting means according to claim 2, wherein the measuring means is a pair of photometric elements corresponding to the pair of line sensors and provided on the back surface of the half mirror. Image forming apparatus. 4. The parallel flat glass corresponding to the pair of line sensors and having a pair of photometric elements on at least one plane provided near the imaging lens. An image forming apparatus comprising the focus detection unit according to claim 1. 5. The measuring means comprises the light receiving means when the imaging lens is moved on the optical axis so that the secondary projection image formed on the surface of the light receiving means is largely out of focus. An image forming apparatus having the focus detecting means according to claim 1. 6. An optical member having an arbitrary refractive power inserted into the optical path so that the secondary projection image formed on the surface of the light receiving means is largely out of focus, and the measuring means is removably inserted into the optical path. 3. The light receiving means as claimed in claim 1.
An image forming apparatus having the focus detection means. 7. A light beam separating means for reflecting a part of an incident light beam on the exit side of the projection lens when the projection image illuminated by the illumination means is projected by a projection lens onto a projection surface such as a screen surface or a recording medium surface. Is provided on the reflection side of the light beam separating means, and the pupil of the projection lens is divided into two regions, and a pair of secondary projection images are formed from the light beams passing through the two divided pupil regions. Re-imaging lens and a pair of light-receiving means composed of a pair of line sensors in the vicinity of the image plane of the pair of re-imaging lenses, the light-receiving means providing relative light amount distributions of the two secondary projection images. When detecting the focus state on the projection surface of the projection lens by detecting the positional relationship, the light amount of the light flux passing through the two divided pupil regions is measured by the measuring means, and the output signal from the measuring means is measured. Based on Image forming apparatus having a focus detecting means, characterized in that so as to correct the sensitivity of the pair of line sensors. 8. The image forming apparatus having the focus detecting means according to claim 7, wherein the light beam separating means is composed of a half mirror. 9. The focus detecting means according to claim 8, wherein the measuring means is a pair of photometric elements corresponding to the pair of line sensors and provided on the back surface of the half mirror. Image forming apparatus. 10. The parallel flat glass corresponding to the pair of line sensors and having a pair of photometric elements on at least one plane provided near the imaging lens. An image forming apparatus comprising the focus detection means according to claim 7. 11. The light receiving means when the measuring lens is moved along the optical axis so that the secondary projection image formed on the surface of the light receiving means is largely out of focus. An image forming apparatus having the focus detection means according to claim 7. 12. An optical member having an arbitrary refractive power inserted into the optical path so that the secondary projection image formed on the surface of the light receiving means is largely out of focus when the measuring means is removably inserted into the optical path. An image forming apparatus having a focus detecting means according to claim 7, wherein the image forming apparatus comprises a light receiving means.