Electrophotographic Microfilm Re-enlarging Apparatus

Abstract

This invention relates to an electrophotographic microfilm re-enlargement apparatus comprising, for optical projection of a negative, an optical system including a plurality of lens means individually insertable into a projection beam and so selected that, with an at least approximately constant projection path, the negative can be projected, at a different enlargement factor for each lens, onto a fixed image plane, and pre-selectable drive means for moving optical elements of the optical system into positions corresponding to each available enlargement factor.

Description

This invention relates to an electrophotographic microfilm re-enlarging apparatus, for use particularly in the field of technical drawing and documentation.

Electrophotographic re-enlarging apparatuses are known in which the supply of copying material is present in the form of rolls or stacked sheets. In known apparatuses using material in roll form with only one supply roll, the applicability of these apparatuses is limited in a manner undesirable in practice, since re-enlargement is possible to at most two sheet sizes. The change to a sheet size not corresponding to the supply roll requires a time-consuming and complicated exchange of rolls. For this reason, the possibility of re-enlarging to smaller sheet sizes than the original sizes, which saves copying material, cannot in practice be realized in apparatuses of this kind.

A re-enlarging apparatus with two supply rolls is also known which is provided with an intermediate image carrier in the form of a photoconductor layer on a rotatable drum. The enlarged projection of the film negative onto the rotating drum necessitates the moving of the negative past an exposure slot at a speed depending upon the enlargement factor required. Apart from the high consumption of mechanical and electrical energy for the optical projection, this process has the disadvantage of a possible lack of sharpness caused by movement during exposure.

The slot-type projection of the negative onto the photoconductor drum does not permit checking or correction of the picture position in the relatively frequent cases of an inexact mounting of the negatives in the film punch cards commonly used. In addition, the toner image transfer process requires a large supply of energy for the fixing of the image on the final image carrier.

Further, re-enlarging apparatuses are known in which the change of the scale of enlargement, required for universal applicability, is carried out by varying the distance of a lens or by exchanging the entire projection components. The adjustment of the enlargement factor by varying the distance requires the complicated simultaneous interdependent variation of image and object distances, for which purpose the entire projection head and the lens in it must be shifted relative to the negative plane. This process is time-consuming and demands, in order to achieve sufficient precision, an expensive construction and an intensive instruction of the operators. Also, when the paper sheet size and the enlargement factor are to be changed frequently, speedy and rational operation is not possible with apparatus in which the projection head must be exchanged when the enlargement factor is varied, because the projection head is unwieldy and heavy and must be readjusted in each case. In addition there is the danger of damage when it is handled carelessly.

Regardless of whether they are to operate with a constant or variable enlargement factor, the known re-enlargement apparatuses with one or several stacks of sheets have the disadvantages that the stacks of sheets particularly in the case of larger sheet sizes, due to their space requirement, adversely affect the size of the apparatus, and that, as experience has shown, the automatic withdrawal of a single sheet from the sheet stack is much more liable to disturbance than the cutting of a sheet of a particular size from a roll. Moreover, the replenishment of the supply of sheets, which requires great care, is cumbersome owing to the additional danger of mechanical damage.

The present invention provides an electrophotographic microfilm re-enlargement apparatus comprising, for optical projection of a negative, an optical system including a plurality of lenses individually insertable into the projection beam and so selected that, with a constant or approximately constant projection path, the negative can be projected, at a different enlargement factor for each lens, onto a fixed image plane, optical elements of the optical system being movable by pre-selectable drive means to bring them into positions corresponding to each available enlargement factor.

Preferably for control of electrical drive means for the movable optical elements, an induction switch system is provided by means of which the elements can be locked in their set positions.

The apparatus advantageously includes, in conjunction with the optical system, additional optical elements by which an image of the negative can for inspection be projected on a suitable screen.

The apparatus normally also will include pre-selectable means for supply, from either or any of a plurality of webs of copying material, a sheet of a size suitable to accommodate an image of a pre-selected enlargement factor.

An electrophotographic microfilm re-enlarging apparatus according to the invention avoids the drawbacks described, may be applied universally, is easy to operate, makes a high copying performance possible, is relatively inexpensive and requires a low consumption of energy.

The invention is illustrated diagrammatically by way of example in the accompanying drawings, in which:

FIG. 1 is a side elevation of one embodiment of the apparatus;

FIGS. 2, 3 and 4 are, respectively, a front elevation, a side elevation and a plan of a reversible drive of a mirror shown in FIG. 1;

FIG. 5 is an elevation showing the copying material supply;

FIG. 6 is an elevation of a cutting device; and

FIG. 7 is a front elevation of the apparatus.

Referring to FIG. 1 of the drawings, for projection, a negative 15, for example that of a film punch card, is illuminated by means of a low voltage point source lamp 16 and a double condenser 17 in such a manner that the image of the point source is formed in the entrance pupil of the lens, the correct distance of the lamp being adjusted automatically when the lens is changed. A heat filter 18 is provided to protect the negative. A film stage, on which the film is mounted, can be pivoted. Three lenses 19 of different focal lengths, positioned in a lens turret, are provided for the projection of the film image onto the electrophotographic copying material. The focal lengths of the lenses are so selected that the projection of the negative, having a fixed position in the apparatus, onto the image plane 9, also having a fixed position in the apparatus, is carried out with approximately equal projection distances. Since the focal lengths of the lenses that can be obtained commercially cannot be matched exactly according to the ratio of the desired enlargement factors, the exact enlargement factor is obtained by parallel displacement, in the direction v of the optical axis of the projection lens, of a first mirror 21 of two mirrors 21, 22 which deflect by 90.degree.. In a preferred embodiment, the focal lengths of the lenses 19 and the projection distance are so selected in conjunction with the mirrors 21 and 22 that adjustment to enlargement factors 7.4, 10.5 and 14.8 is possible.

The exposure time is automatically changed over by selecting the enlargement factor 77 (see below FIG. 7), in accordance with the ratio of the areas of the image plane exposed in the case of each of the enlargement factors to be set. If the ratio of the enlargement factors a:b:c is about 1:.sqroot.2:2, the ratio of the exposure times a.sup.2 :b.sup.2 :c.sup.2 must be 1:2:4, for example.

In a simpler manner the result is thereby achieved that no manual adjustment of the exposure timer is necessary when the enlargement factor 77 is changed during the enlargement of negatives of approximately equal density. In addition, the relative sensitivity to adjustment remains the same when the enlargement factor is changed, so that the angle by which the adjustment knob 89 (see below with reference to FIG. 7) for the exposure timer is turned to compensate for a particular density difference is the same for all enlargement factors.

All movements of the optical elements shown in FIG. 1, such as the point source lamp 16, the lens turret 20 with three lenses 19, mirror 21, mirror 26 and diaphragm 27 behind a ground glass screen 25, are effected by reversible drives free from play, coupled undetachably and elastically with the optical elements, which is illustrated by way of example for the mirror 21 in FIGS. 2, 3 and 4.

A main guide shaft 34 and counter guide shaft 35 are mounted between two bars 31, 32, positioned in a stationary housing 33. Two slotted ball races 36 with an adjustable bearing flange 37 are arranged on the main guide shaft. The counter guide shaft 35 accommodates a ball bearing 38 with stay bolt 39 and pressure pin 40. Both are attached to a flange plate 41 which serves to accommodate the housing for the mirror 21. A drive motor 42 with brake is arranged on the flange plate 41. Preferably, a synchronous motor 42 with a permanent magnet is built in. A drum 43 is arranged on the drive shaft of this motor. A cable 44 runs from the righthand bar 31 with a single turn around the drum 43 to the lefthand bar 32 where it can be tensioned by means of a take-up screw 45. On the flange plate 41 there is also an extension 46 with a control vane 47 of thin steel plate of a material width x. This control vane 47 moves through four induction switches 48 which are constructed as slot initiators. They can be adjusted axially on a setting bridge 49.

Mechanical ratchet notches 50 are arranged above the stationary housing 33, being adjustable by axial movement.

A ratchet pin 51 with a roller 52 is guided in a ball race 53 which is mounted in an adjustable housing 54. Lateral forces can be taken up by this means, without tilting the ratchet pin 51. A coil spring 55 with adjusting pin 56 provides adjustable counter forces. An intermediate plate 57 connects the housing 54 with the bearing flange 37.

Four inductor switches 48 are arranged for three notches 50, the middle two inductor switches being appropriate for one enlargement factor. Since the control vane 47 has a material width x, the control edges of this vane are separated by a distance x when the motor is rotated to the left or to the right, and therefore the middle induction switches 48 must be separated by a distance x. Depending upon the direction of rotation, one or other switch of this twin arrangement is caused to function.

By selecting the enlargement factor, the corresponding induction switch 48 is actuated; the direction of rotation of the motor 42 is so controlled by a logic circuit that the switch is started by the shortest route. The rotation is transmitted to the drum 43, which traverses the tensioned cable.

When the edge of the control vane 47 has uncovered the induction switch up to its switch-over point, it switches off the drive motor 42 accurately and exactly. Within 50 microseconds the motor brakes itself by means of its permanent magnet and engages with the pin 51 into the corresponding notch 50. By adjusting the induction switch 48 on the setting bridge 49, the switching-off of the motor can be co-ordinated so exactly that when the pin 51 engages in this notch 50, it has no residual kinetic energy.

A ground glass screen projection system is provided for the optional checking of the film picture as regards picture content and position in the picture window. The checking is carried out with a separate lens 23 (FIG. 1) and a fixed enlargement factor of about 6. The adjustment is achieved by means of three regulating knobs 24 which rotate the film stage and shift it up or down and sideways. The correct position of the film picture can be determined by means of size markings on a ground glass screen 25 (FIG. 7).

When the ground glass screen projection is switched on, the projection lamp 16 is conveyed to a point which is the correct distance from the lens 23 used for projection, the first mirror 26 of the ground glass screen projection system is moved from the side into the path of the beam, the diaphragm 27 behind the ground glass screen which during the copying process prevents the entry of extraneous light, is retracted, and the projection lamp 16 is switched on. On the exit side of the lens 23, there is provided a pentagonal prism 28 and two planar mirrors 29, 30. The steps proceed in reverse when the ground glass screen projection is switched off manually, or automatically by operating a starter button 82 for the copying process.

The microfilm re-enlargements are produced on electrophotographic copying material, in particular on zinc oxide paper. The supply of material is stored in the form of two rolls 1 and 2 on spindles with braking and friction devices 58, at least three different sheet sizes, preferably standard sizes, being available. The leading ends of the material rolls are threaded into a common withdrawal device 3 which comprises the transport rollers 4, two inlet slots 5 and the return elements 6.

In the preferred embodiment of the apparatus, the two inlet slots 5 and a holding-down element 59, which operates continuously, form a common structural member (FIG. 5).

The inlet slots 5 are conical shafts with an aperture of between 10.degree. and 30.degree. which are formed by an acute-angled wedge-shaped sheet metal plate 60 and cover sheet metal plates 61. The wedge-shaped sheet metal plate 60 has an extension in the direction of the bisector of the angle, which extension forms together with the plates 61 two channels of height h, at the holding-down element 59. This structural member fulfills surprisingly well and in the simplest manner the purpose of the trouble-free feeding of a web 62 of copying material to the cutting device 7, and of holding it for the cutting step. However, to immobilize webs of material of greater width, flanges or beads are fixed to the wedge-shaped or cover metal plates, preferably in the region of the holding-down element 59. They may extend over the entire width of the material web or over only part of it.

The height h of the slot is as small as possible in order to guide exactly and stabilize the web 62 of copying material. However, the lower limit of the height of the slot depends upon the technical properties of the web and the selected feed speed. The slot height ranges from double the thickness of the web of material to about 3 mm.

In one embodiment of the apparatus, in which the 75 to 100 micron thick and 297 or 420 mm. wide copying material is fed at about 10 meters per minute, a holding-down element of a slot height of 0.5 mm. has proved useful.

The feed of the copying material is effected by a roller system consisting of two transport rollers 4 and a pivoted roller 63. All three rollers are coated with rubber or plastic material in order to improve their grip when withdrawing the webs of material.

The transport rollers 4 are arranged at the smallest effective distance from the inlet slots 5. The bisectors of the aperture angles form tangents to the peripheries of the transport rollers. Only one pivoted roller 63 is provided for the two transport rollers and it presses against one or other of the two transport rollers 4. When at rest, the roller 63 is positioned geometrically between the two transport rollers 4.

The fixed axis transport rollers 4 which are adjusted relative to the image plane 9 are coupled to a continuously running chain drive by electromagnetic couplings. In the preferred embodiment, the pivoted roller 63 is free running, and this is particularly advisable in the case of greater widths of the material web, approximately over 500 mm. The pressing of the pivoted roller 63 against one of the transport rollers 4 may be effected for example, by an electromagnetic twin stroke magnet 64. Instead of the twin stroke magnet 64, other known alternatives may be employed.

The transport rollers 4 are at rest before and after each copying material feed step, the roller 63 is at its middle position and the webs of material 62 hang in loose loops over the return elements 6, until an electrical impulse simultaneously excites the electromagnetic coupling which is mounted on the transport rollers for the transmission of the rotary motion, and the twin stroke magnet 64 for pivoting the roller 63 into the direction determined by the selection of the re-enlargement sheet size, so that the roller 63 presses against the corresponding transport roller 4. In this manner, the copying material positioned between these two rollers is withdrawn from the corresponding supply roll. The return element 6 is also urged out of its null position by the material itself being gradually tautened. The couplings of the transport roller 4 and the twin stroke magnet 64 of the roller 63 remain excited until the cut is made. After the cutting operation, the roller 63 returns into its middle position so that the return element 6 can retract the web of material by the set distance.

The construction of the return elements 6 is different for the upper and lower supply rolls 1 and 2. A rotatable, lightly braked roller 6a, coated with soft material, preferably rubber, runs over the coated side of the upper web of copying material. The back of the lower web of copying material is pulled over a table 6b provided with prevention means 65 against reverse movement of the material. Both return elements are pivotally suspended and their path is limited by adjustable stop screws of conventional construction.

Free-wheeling rollers, blocks of plastic foam or lever mounted brushes of known construction may also be used for prevention of reverse movement of the material.

The return elements 6 which are urged out of the null position by the material web tautening when fed in, become stabilized during the advance of the material web, by their own weight or by the tension of the material web. After the cutting step is completed with simultaneous interruption of the feeding of the copying material, as described above, the return elements retract, by their own weight or by spring tension, the web of material from the cutting device 7 into the respective inlet slot 5 or holding-down element 59. Thus the possibility is avoided that the webs from the supply rolls may touch and interfere with one another when the feeding of the material is renewed, and that the web of material not selected may be carried by the selected web of material towards the knife. In the idle position, the web of copying material hangs as a loose loop over the return element, or it is held by the device 65. Thus the possibility is avoided that the loose web of material may slide back from the holding-down element 59. The return elements of the apparatus of the invention have the advantage that renewed withdrawal from the supply roll is carried out smoothly and gently even at high speed, whereby in particular any damage to the sensitive photoconductor layer is avoided.

Arranged immediately adjacent the withdrawal device 3 is the cutting device 7 which is controlled for the cutting by the leading edge of the web of material by way of knife switches 66a.

Scissor knives, rotary knives or roller knives are used and the cutting edge of the upper knife may have a variety of V or W-shapes. In the case of rotary or roller knives, the correct cutting angle is obtained by eccentric mounting of the knife. The known devices have the common disadvantage that the knife edge moves perpendicularly to the web of material to be cut, whereby, due to the rectilinear impact of the cutting edge, the photoconductor layer is fragmented. The fragments settle mainly in the path of the knife, so that the knife jams after a relatively short operating time and therefore has an unsatisfactory service life.

In the apparatus according to the invention, on the other hand, settling of fragments on the knives and resulting breakdown of the cutting device do not occur.

The cutting device (FIGS. 5 and 6) is constructed as an independent unit which can be inserted in the apparatus. It includes a base mounting 67, a counter-blade 68, a cutting blade 69 with two guide levers 70, 71 of different lengths, an electromagnet 71a of known construction and a return spring 72 for the cutting blade.

Parallel to the plane 73 of the web of material and below it, the blade 68 is let into the lower part of the base mounting 67 in such a way that it is fixed only at the end at which the cut commences and is urged by a spring 74 against the cutting blade 69.

The cutting blade 69 is pivotally mounted above the web of material by means of the shorter guide lever 70 at the side of the beginning of the cut, and a longer guide lever 71, preferably of double the length, at its other end, in such a manner that during the cutting process a constantly changing cutting angle is obtained. In one embodiment, a cutting angle of 4.degree. at the beginning and of about 20 minutes at the end of a 420 mm. long cut have proved of particular advantage.

In the apparatus of the invention, the cutting knife 69 penetrates with a constantly increasing cutting speed obliquely from above and from one side into the web 62 of material to be cut. In co-operation with the blade 68 the result is achieved at the same time that during the cutting operation always only a point contact of the cutting edges of the two knives takes place and that the cutting edges maintain themselves sharp.

Arranged in sequence after the knife is an electrostatic charging station 8, in the form of a corona discharge device, for the uniform charging of the photoconductor layer. After charging, the electrophotographic material is taken up by electrostatically charged transport belts 9, which at the same time constitute the exposure plane. After exposure by means of the projection device, the transport belts transmit the sheet to a developing station 10. There, dispersion developer is sprayed from a slot die 11 onto the upper side of the electrophotographic material and excess developer is removed by means of a pair of nip rollers 12 made of elastic material which are pressed together only when the apparatus is switched on. The finished copy is dried by an air current 14 before reaching a collecting basket 13.

The guiding of the sheets through the cutting-, charging-, exposure- and developing stations 7, 8, 9, 10 in a near-horizontal plane, together with the provision of the copying material in the form of rolls, renders it possible to make the apparatus of relatively small dimensions, while the advantages of stationary exposure are maintained. By avoiding all detours, the path to be travelled by the copying material, which path is substantially determined by the dimensions of the largest re-enlarging size, becomes relatively short and, with accurately controlled transport speeds of the copying material, the copying performance is therefore greater than in apparatus with a different method of guiding the material. In addition, the guiding of the copying material according to the invention renders it possible to deliver copies at a height convenient for the operator. Further, substantially horizontal transport of the copying material ensures, in a simple manner and with the use of a minimum number of transport elements, the smooth and faultless guiding through the processing stations even of thin and not very stiff copying material and thus achieves extraordinary reliability of service.

Moreover, by exploiting the possibilities of the electrophotographic process operating with development by liquid, the apparatus has an extraordinarily small power consumption.

Sequence of operations:

By means of a key-type switch 75 (FIG. 7), the pair of nip rollers 12 in the developing section are brought into the pressure position and the main relay is switched on, whereby the main drives of the apparatus, the current supply for the electronics, the charging of the transport belts 9 and the developer circulation are also switched on. The apparatus is then ready for use and a negative can be inserted.

By pressing the key 76 for the screen projection system, the following processes are automatically initiated: Mirror 26 and the diaphragm 27 of the ground glass screen 25 moves into the operating position and the projection lamp 16 moves into the position for ground glass screen projection, whereupon the lamp lights up. The image appears on the ground glass screen and can be adjusted if desired. On renewed pressing of the key 76, the projection lamp 16 goes out and the mirror 26 and the diaphragm 27 and the ground glass screen 25 revert to their starting positions.

Now, data for the required number of copies 79, the enlargement factor 77 and the sheet size 78 may be fed in, although this could have been done previously. The following are possible combinations: ##SPC1##

When one of combinations 1 to 4 has been selected, a horizontal arrow 87 in the fascia board of the apparatus lights up to indicate that the film stage must be in the position provided for lateral insertion of the film punch cards. If this is the case, the apparatus is ready for further operations. Otherwise, the apparatus remains locked until the negative is turned into the corresponding position. When combination 5 or 6 is selected, a vertical arrow 88 lights up and similar conditions apply. When combinations 7 to 9 are selected, the "over-size" sign 80 appears. The apparatus is again locked. When an admissible combination has been selected, the following drives are automatically switched on: drive for projection lamp adjustment, drive for the lens turret head 20 and drive for the mirror 21. In accordance with the preselection, they are moved by the shortest route into the prescribed positions. After arrival, the green "free" sign 81 appears. The machine is again ready for further operation.

On actuating the "start" key 82, the keys for enlargement factor and sheet size are locked in place. The "free" sign goes out. Further, the coupling of that transport roller 4 which has been actuated by the selection of the sheet size and the magnet 64 of the roller 63 are switched on in the direction determined by the choice of sheet size, and the corresponding copying material is taken in. The corona discharge voltage is also switched on. When the leading edge of the material reaches the knife switch 66a (FIG. 1) pre-selected by the selection of the sheet size, the operating lever of which switch lies in the path of the material web, the cut to the correct sheet size is carried out. At the same time, the magnet 64 of the roller 63 and the coupling of the transport roller are switched off. After the leading edge of the material has reached the image stage switch 66b (FIG. 1) pre-selected by the combination of enlargement factor and copying material sheet size, the operating lever of which switch also extends into the path of the web of material, band transport and corona potential are switched off and the exposure timer is switched on, which in its turn switches on the projection lamp for the duration of the exposure time to which it is adjusted. At the end of the exposure period, the exposure timer controls the copy counter 90 and initiates the next copying process. The exposed copy is led to the developing section, developed and delivered from the apparatus. After exposure of the last of the copies to which the number selector is set, there remains only the transport of this copy to development and further processing. When the entire copying process is completed, the locking of the control device is automatically released.

A "stop" key 83 is provided for interrupting the copying process, in which case the last copying step initiated is completed. The interrupted process can be resumed by pressing the "start" key 82.

When the roll of copying material is exhausted, the web of material, which then takes up a radial position with respect to the core of the roll, its end being fixed to the core of the roll, actuates a corresponding switch. Optical indication of this situation is effected by the lighting-up of tell-tale lamps 84. A copying step already started is completed and the apparatus is then locked. After insertion of a fresh roll to render the apparatus again ready for operation, a further switch, not shown, must be actuated, which cancels the switch previously mentioned.

A further control lamp 85 in the fascia board of the apparatus lights up when the amount of developer in the supply container is exhausted, except for a residual quantity, the amount of which can be adjusted.

To maintain the correct toner concentration, a predetermined further amount of toner can be introduced by actuating a "toner" key 86.

By switching off the main switch, firstly the servo-motor of the nip rollers in the developing section is actuated so that the rollers separate. After reaching the terminal position, the main relay is switched off and the apparatus becomes inactive.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

Claims

What is claimed is:

1. An electrophotographic microfilm re-enlargement apparatus comprising, for optical projection of a negative, an optical system including a plurality of commercially available projection lenses individually insertable into a projection beam and so selected that, with an approximately constant projection path, the negative can be projected, at a different enlargement factor for each lens, onto pre-selected locations of a fixed image plane, and pre-selectable drive means for moving optical elements of the optical system into pre-selected positions, the locations in the image plane and the corresponding positions of the movable optical elements being selected in accordance with the focal length of the respective lens whereby the exact enlargement factor is obtained.

2. An apparatus according to claim 1 including, for control of the drive means for the movable optical elements, induction switch means whereby the said elements can be locked in their set positions.

3. An apparatus according to claim 2 including, for each movable optical element, a synchronous motor with permanent magnet, the switching-off of which by a corresponding induction switch means being controllable such that an element employed for locking reaches its locking position with substantially no residual kinetic energy.

4. An apparatus according to claim 2 in which each drive means is contained in a logic circuit for moving the corresponding optical element from one set position to the other by the shortest route.

5. An apparatus according to claim 1 in which adjustment of the movable optical elements can give enlargement factors of 7.4, 10.5, and 14.8.

6. An apparatus according to claim 1 including exposure timer means so connected to means for setting to a particular enlargement factor that upon effecting such a setting the exposure timer is set to a time which varies with the square of the set enlargement factor.

7. An apparatus according to claim 1 including, in conjunction with the optical system, additional optical element means whereby an image of the negative can be projected on a screen for inspection.

8. An apparatus according to claim 1 including pre-selectable means for supplying to a cutting means, from one of a plurality of webs of copying material, a sheet of a size suitable to accommodate an image of a pre-selected enlargement factor.

9. An apparatus according to claim 8 including, for alternative supply of two webs of copying material, withdrawal means comprising a transport roller for each web and a pivoted roller for cooperation with either transport roller to feed one of the webs, and guide means for each web so fed, each guide means including an inlet slot, a confining element, a return element to retract the web from the cutting means, and means for prevention of reverse movement of the material.

10. An apparatus according to claim 9 in which the inlet slots and confining elements are accommodated in a single structural member.

11. An apparatus according to claim 1 so arranged that in its passage through a cutting, a charging, an exposure and a development section of the apparatus, the web or a sheet cut therefrom proceeds in a horizontal or near-horizontal plane.

12. Apparatus according to claim 1 the movable optical elements of which consist of mirror means which deflects by 90.degree. and is movable in the direction of the optical axis of the projection lens.