chuck colburn
Well-known member
Driving down the street a couple of days ago I spotted a photographic enlarger sitting on the curb in front of a house. Quickly pulling over I found it to be an as new Bessler 67CXL with a Schneider 50mm Companar enlarging lens on it and a free sign taped on it. (This town has to much money) So I tossed it in the back of my truck and took it home. I then made a copy of a Siemens star on the computer printer and slipped it into the neg holder of the enlarger. Then I took my old Pentax Spotmatic and mounted a prime lens that I knew was spot on at the infinity mark on the barrel. Having the XL column helped me be able to lay on the base and look through the camera eyepiece at the projected image of the star target. Then I racked focus on the enlarger untill I got a nice sharp image of the star target in the eyepiece of the camera. I know this was the equivalent of infinity focus as it did not vary no mater how close or far I held the camera body from the enlarging lens. While the exit pupil did not fill the whole frame of the ground glass, it did provide a sharp image of the center of the star target. (Zeiss uses a 200mm achromat on their Sharpmax unit and mayby some additional optics I don't know about) but anyhow it proves that one could build a "Sharpmax type tool for a lot less then it would cost to buy one. You can buy etched star or resolution targets on 2" square glass substrates and combine it with a simple achromat lens and a led light source (perhaps one of the new led minimag lights with a little diffusion material mounted on the back of the substrate) pop it all into a machined housing and have your own poor mans "Sharpmax".
Just another thought or two about generating a target for a home built tester. Make a high rez copy of a siemens star on you printer and sandwich it between to layers of glass and the paper itself would act as a diffusion material to even out the light from the led source. Or if you can find one, use a glass mount slide holder.
Here's a source for surplus optics and such.
http://www.surplusshed.com/pages/item/l3035.html
Just another thought or two about generating a target for a home built tester. Make a high rez copy of a siemens star on you printer and sandwich it between to layers of glass and the paper itself would act as a diffusion material to even out the light from the led source. Or if you can find one, use a glass mount slide holder.
Here's a source for surplus optics and such.
http://www.surplusshed.com/pages/item/l3035.html