DE2628833A1 - Microfilm reader with self adjusting illumination - has photocells controlling adjusting motor to cope with ambient light and/or density of film image - Google Patents

Abstract

A light-sensitive element registers the ambient light. In addition, or instead, another light-sensitive element measures the density of the microfilm image, pref. at the edge. In either case, a manual adjuster is provided, to allow the user to set the level which the machine will thereafter maintain, thereby obviating continual manual adjustment by the user. The automatic adjustment of illumination is made by altering the position, and therefore density, of a variable-density filter in the light path, by means of an adjusting motor which is electronically controlled from the photocells.

Description

Microfilm reader

The invention relates to a microfilm reading device with an electrical Illumination device for illuminating the micro-image to be viewed, a screen for viewing the image projected on this screen and a facility for changing the brightness of the projection light.

In such known type microfilm readers, the user has the Possibility to adjust the brightness of the projection light according to the one you want Adjust the screen brightness manually.

The invention is now based on the object of a microfilm reading device to create at what the screen brightness. automatically depending on the parameters influencing optimal screen brightness for the user are set will.

According to the invention, therefore, the ambient light outside of the reading device is measuring photosensitive element provided, the measuring signal of which the device controls to change the brightness of the projection light. This increases the ease of use of the reader increased significantly, since the user is now with frequent changes the ambient light is no longer the required screen brightness by hand must readjust.

To solve the problem on which the invention is based is furthermore according to the invention, a photosensitive device measuring the transparency of the microfilm material Element provided, the measurement signal of which the device for changing the brightness of the Projection light controls. This means that constant screen brightness is independent of varying densities of different film materials in a user-friendly manner achieved.

According to a further feature of the invention, this is the transparency of the Light-sensitive element measuring microfilm material in the projection beam path arranged, dan it measures the brightness of an edge zone of the projection light, whereby the. usually unlabeled and therefore for the optical density of the film material representative edge zone of a microimage is scanned.

Further advantages of the invention are the remaining subclaims in Relation to the following description, in which based on the drawing explains a preferred embodiment of the invention in more detail is. In the drawing, FIG. 1 shows a section in a semi-schematic representation by an Elikrofilmreadersgerät, Fig. 2 the actuating mechanism for a in the Projection beam path pivotable gray filter and FIG. 3 is a basic circuit diagram the control or regulating device for the gray filter.

In Figure 1, a lighting lamp is in the lower part of a device housing 1 2 housed with reflector 3, through which lenses 4.5 and a deflecting mirror 6 the microimage to be viewed is illuminated. This Nikro picture is on a microfiche 7, which in a manner not shown in detail the equipment house in two coordinate directions displaceably mounted transparent Microfiche platform 8 lays The micro image to be viewed is produced by means of an imaging lens 9 via deflection mirror OK, 11 shown on an enlarged scale on a ground glass screen 12.

In the imaging beam path 13 is an objective 9 above the imaging Gray filter 14 is provided, which is pivotable on an axis 15 fixed to the device 16 is attached. This gray filter has an increasing shade of gray in the direction of arrow A. so that by pivoting the gray filter more or less shaded areas of the gray filter can be brought into the beam path and thus the brightness the imaging beam path can be weakened more or less.

A servomotor 17 is provided for pivoting the gray filter, which drives a gear 19 via a drive shaft 18. This gear 19 acts with the teeth 16a of the holder 16 together.

A photocell 20 is attached below the ground glass 12, which measures the ambient brightness of the reader over a large angular range. One Another photocell 21 is inside the device in the edge zone of the imaging beam path 13 and measures the transparency within a narrow angular range of the microfilm material used.

The mode of operation of the device for controlling described above the projection brightness is shown in FIG. Using a specific microfilm material and at a given ambient brightness, the user sets by means of a setpoint adjuster 22 the optimal projection brightness for him, whereby by means of the servomotor 17 the gray filter 14 in the position corresponding to this setpoint value in the beam path 13 is pivoted. Every change in the ambient brightness is monitored by the photocell 20 detected and forwarded to the control device 23, which corresponding output signals for controlling the servomotor 17 supplies. By means of the photo cell 21, the Control device 23, the servomotor 17 and the gray filter 14 formed control circuit If the transparency of the microfilm material changes, the brightness of the projection light becomes kept at the desired brightness level.

Claims (5)

Claims 1. microfilm reader with an electrical lighting device for illuminating the micro-image to be viewed, a screen for Viewing the image projected on this screen and a facility for Change in brightness of the projection light, characterized in that a Light-sensitive element (20) measuring ambient light outside of the reading device is provided, the measuring signal of which the device for brightness change (ilt to 19) of the projection light controls. 2. Microfilm reading device with an electrical lighting device for illuminating the micro-image to be viewed, a screen for viewing the image projected on this screen and a device for changing the brightness of the projection light, characterized in that the transparency of the micro film material measuring photosensitive element (21) is provided, the Measurement signal the device for Change in brightness (14 to 19) of the Projection light controls. 3. Microfilm reading device according to claim 2, characterized in that the light-sensitive element (21) is arranged in the projection beam path (13) is that it measures the brightness of a peripheral zone of the projection light. 4. Microfilm reading device according to one of the preceding claims, characterized characterized in that a setpoint adjuster (22) for the brightness of the projection light is provided. 5. Microfilm reading device according to one of the preceding claims, characterized characterized in that in the beam path of the illumination lamp (2) a gray filter (14) is arranged, which along a direction (A) an increasing gray color has, and that a servomotor (17) cooperating with this gray filter is provided is, softer depending on the measurement signals of the light-sensitive elements (20,21) Filter sections of the required gray coloring in the beam path of the illumination lamp brings in.