Making one good microscope out of 3
by Bill Resch, USA

During this long Minnesota winter I had to find something fun to do. I noticed this old American Optical frame sitting in my basement. It is from a "Radius Scope", designed to measure contact lenses. Somebody gave it to me years ago. It did not have a stage. I made one a while ago from some aluminum stock. I never used the instrument. The illumination was from the top through a 4X objective (the only one). My stereo scope did a better job viewing subjects from the top.

I had to do something with this instrument to make it usable.

I went on eBay and found several AO microscopes at a very low price. I bought an American Optical 160. It had 3 objectives, a mechanical stage and an illuminator in the base, which was just a bulb behind a ground glass. I got it for only $47. It did have a broken revolving nose piece. The ball bearings were missing. It was just hanging in there loosely. But the nose piece itself was fine. It was a four objective nose piece. I fitted it to the Radius Scope. Now I had a four objective microscope.

I wanted a better illuminator. So I went on eBay again and found an AO 150 for $15. No optics, but it had a low voltage halogen illuminator with intensity control. There was also a lens after the ground glass. Not Köhler, but better than the 160. It also had a focusable substage condenser with diaphragm and filter holder. All the items a hobbyist likes.

There was one problem though: Somebody must have dunked the whole thing in oil. I had to do a lot of cleaning. The hard part was the diaphragm. The oil was so heavy, I could not open or close it. I overcame my fear and took it apart. I cleaned the blades with automotive break degreaser. That stuff is effective.

Putting the diaphragm back together was another story. I tried all kind of ways. I checked past "Micscape" articles. That helped a little, but I had a different brand. I finally made a tool to hold the blades pushed out and held down. With all the blades laid, I inserted the tool. Now I could move them with a needle until they dropped into their individual hole. If you ever had one of these apart, you know what I am talking about.

The tool: I turned it out of 1.5 inch aluminum stock. The diameters are critical and are given in millimeters.

This unit happened to be about 30 mm high. The weight helps to hold the blades down. The small diameter ring should be polished. It would help, not to lift the blades up when you remove the tool. When the blades are all in place, (you can see that on the height of the tool), you can lay the lever on top and screw it down. Do not oil or grease!

It worked like a charm after the cleaning and assembly.


The 150 on the left and the 160 on the right.

The finished product.

I had to test it by taking a photomicrograph. I used a Kodak C653 and held it against the eyepiece. I zoomed in until there was no more vignetting. I used a slide from Turtox, labeled: Pleurosigma angulatum. The objective is the AO 43X NA 0.55. Actually not good enough for this subject. I could hardly perceive the grid. I was amazed when I uploaded the picture.

Pleurosigma angulatum. AO objective 43X, NA 0.55. Right half of condenser covered.

Final thought:

I was impressed with American Optical. Infinity correction objectives 50 years ago, (now everybody is doing it). The focusing mechanism: The nosepiece is just held down by gravity. No need for springs for protective retraction in the high power objectives. The focusing mechanism is virtually wear proof, no maintenance. The objectives I ended up with are from quite a variety of instruments. Some from student, some from lab microscopes. There is at least a 20 year difference in manufacturing time. They all fit, are par focal and perfectly par centered. That is quality. Too bad, they are out of this business.

All comments to the author Bill Resch are welcomed.


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Published in the February 2008 edition of Micscape Magazine.

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