American Optical Series H20 This microscope was made in mid-1970s, but it is still in a great shape and delivers very nice pictures. You can find a manual for the AO-20 here. Steve Neeley has collected a vast amount of information about American Optical and Spencer microscopes on his excellent website. I sold the AO-20 microscope in 2004. This microscope is equipped as follows: objectives (all infinity corrected) mounted in a quadruple nosepiece: 4x plan achromatic objective, N.A. 0.12 10x achromatic objective, N.A. 0.25 45x achromatic objective, N.A. 0.66 50x oil immersion plan achromatic objective, N.A. 0.80 100x oil immersion achromatic objective, N.A. 1.25 10x dark contrast phase achromatic objective, N.A. 0.25 20x dark contrast phase plan achromatic objective, N.A. 0.50 45x dark contrast phase achromatic objective, N.A. 0.66 dual binocular body with 10x wide field eyepieces and green arrow pointer 12V 100W halogen light source with centerable field diaphragm and condenser focusing controls Abbe condenser N.A. 1.25 with aperture diaphragm, on focusable rack and pinion mount aplanatic-achromatic turret phase condenser N.A. 0.90 with four phase annuli darkfield bispheric condenser rotatable polarizer attachment and analyzer unit with 3-position turret two built-in 5-position filter turrets graduated mechanical stage coarse and fine focusing knobs with "auto focus" feature ExpoStar automatic camera controller with shutter attachment, 35 mm film back, and 3 1/4"  x  4 1/4" Polaroid back 10x field of view focusing eyepiece filar micrometer epi-fluorescence attachment with three excitation filters, three dichroic mirrors and three barrier filters viewing screen