The instrument can be used for testing the adaptation of lenses directly on the camera as well as for identical testing of the flange focal length (distance lens – film-plane) of interchangeable lenses. Moreover the equipment is well suited to check the alteration of the image plane when zoom-lenses are used (error in the control curve). Furthermore testing of the adjustment of reflex view finders with ground glass or aerial image is possible.
With the standard autocollimation method for testing the adaptation of lenses the lens is adjusted so that the observer sees the image of a finely graduated test figure of an autocollimation telescope with identical sharpness to the eyepiece reticle of the autocollimator telescope. The colour change process is also used in which instead of the finely graduated test figure a bright cross-wire on a dark background is used. The image of the cross-wire illuminated with white light in the eyepiece image plane of the autocollimation telescope shows colour fringes if the lens is not correctly adjusted.
With the new process it is not the sharpness of the image which is the criterion of adjustment, but the symmetrical position of position of a single line within a double line. This dispenses with the differing and subjective interpretation of the image sharpness.
The display of the image on a monitor and the mode of symmetrical adjustment allow a largely fatigue-free working in mass production.
With the same instrument the basic lens in relation to the film plane can also be adjusted. If in account of practical experience the setting to a finite distance be required, the testing instrument can be supplied with an extension unit. The extension unit can be set by using a master sample.
The Camera Testing Instrument III is equally suitable for setting of lenses in miniature and half-plate cameras in mass production.
With the procedure used, the setting is made at the centre of the image as is also the case with the autocollimation and collimation method. This won't in all cases be an optimum setting over the entire field of view because of off-axis errors (field of curvature, astigmatism, coma). Averaging of the image quality over the field of view will often be favourable of necessary. The deformation of film is additionally to be considered.