1990x4 - Λούπα Anastigmatic - 10x
The 1990-4 Loupe with 4X magnifying power is specially designed to enable observers to simultaneously inspect the whole picture area of the standard micro-film size (i.e. 32mm x 45mm) or flat objects less than 58mm in diameter. The image observed through the loupe is critically sharp from the center to the edge of the image field, because of the careful optical correction of the loupe for the astigmatism and the curvature of the field as well as aberrations concerning the image of the central image. Ordinary magnifiers are corrected only for the central image. In this respect, this loupe is quite similar to anastigmatic photographic lenses, and is manufactured with the same care and precision.
One point which distinguishes this loupe from photo-lenses is that the position of the effective pupil of the loupe has been placed as far as 25mm above the upper pole of the loupe; so that an observer can inspect the whole image field by merely moving his eyeball, without moving his face. This is an extremely advantageous feature for a micro-filmer, because it enables him to inspect a number of negatives very speedily and comfortably.