American Optical series 20 microscope illumination

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
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bcjolly
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Joined: Sat Jul 06, 2019 2:50 am

American Optical series 20 microscope illumination

#1 Post by bcjolly » Tue Aug 09, 2022 1:53 am

I have an American Optical series 20 that I have been working with for 3 years. The instrument is in excellent cosmetic and mechanical condition. However I have been unable to achieve a uniform level of illumination across the field of view. The illumination bulb can be seen and it’s very evident that some areas are brighter than others. Rotating the lamp holder does not mitigate the problem. I am beginning to think that maybe some part is missing. Does this microscope have a frosted glass filter in the light path that may be missing? I have not been able to achieve even, flat illumination across the field of view with any of my efforts. Seems like the situation is exacerbated with lower power objectives.
bcjolly

apochronaut
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Joined: Fri May 15, 2015 12:15 am

Re: American Optical series 20 microscope illumination

#2 Post by apochronaut » Tue Aug 09, 2022 11:23 am

There were several versions of the 20. I have seen them with and without the primary heat resistant collector lens being frosted. It may have to do with the ultimate use the microscope was put to because many of them were fluorescence microscopes. There is one sitting here without a frosted collector lens. When finally it gets cleaned up and lubricated I had planned to just install a ground glass filter in the filter carousel . I bought a few ground and lightly tinted blue to be used with a few microscopes and they work well. There is lots of light, so the minimal absorption of such a fiter is irrelevant. There should be an extra to fit the 20 filter wheel. I probably have 5.00 in them.

You know, the 20 has to be one of the best used microscope deals available out there. They are usually, cheap, cheap and once kitted out with 1021, 1022, 1309 and 1311 objectives and a trinocular it would cost you $2000.00 to buy the equivalent of it new. Add in a 214F D.F. condenser and a 1014 objective for a lovely high resolution D.F. instrument. Sturdy. That objective group are " advanced planachros". While AO did make some planapos for the 20, they did not make any planfluors. My reading of the term "advanced planachro" is based on comparative testing of them. My best guess is that although they do not have any fluorite elements in them, they do contain L.D. glass. Their performance is very reminiscent of a planfluor.


I looked into a Chinese 100 watt D.F. scope with trinocular (R.M.S.) and it wss 2600.00 with a DF condenser and iris equipped planachro. It's only major advantage over a 20 was a 23mm head.

bcjolly
Posts: 31
Joined: Sat Jul 06, 2019 2:50 am

Re: American Optical series 20 microscope illumination

#3 Post by bcjolly » Wed Aug 10, 2022 12:58 am

Thank you for your reply. I ordered 4 frosted filters for my microscope. Will see how that works out. My AO20 came from a hospital in Chicago but I have forgotten the name. Main reason I bought it was its excellent condition. It’s like brand new. Thank you for the list of objectives. I will be looking to add them to the collection for this scope.
bcjolly

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: American Optical series 20 microscope illumination

#4 Post by apochronaut » Wed Aug 10, 2022 11:14 am

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About 10 years ago that was considered. Researchers participating in a U of Amazon/ Twitter U. study, conducted tests on 10 microscope brands, using collecting lenses made out of the traditional heat proof glass, carbonated water, fused peach fuzz, green aphid exudate, laminated onion membrane, depilated merkin , lard and interestingly yuca fries.
The results were encouraging because all of the test compounds with the notable exceptions of the depilated merkin and yucca fries were useable, at least temporarily, and since laminated onion membrane showed an improved dissipation of illumination rays laterally , researchers expressed hope that in future a completely carbon neutral , biodegradeable alternative to conventional collecting lenses would be manufactured.
This was a controversial study because although glass is not organic and not biodegradeable, it is derived from a natural source and upon completion of it's manufactured task can be recycled or returned to it's natural environment. The argument was also made by one of the researchers E. Musk, that on some planets that he was familiar with, glass is biodegradeable.

rmb
Posts: 35
Joined: Fri Dec 01, 2017 5:38 pm
Location: scotland near Edinburgh

Re: American Optical series 20 microscope illumination

#5 Post by rmb » Mon Aug 22, 2022 2:05 pm

I too have versions with frosted and clear glass in the collector lens. Whilst we are on the subject of AO illumination. Having acquired mine from the US without power for their halogen lamps - and as previously trailed - some pictures of the LED conversion. This is sufficient to power all techniques including DIC and phase contrast. Since the thing is glued together with thermal glue it could be reversed - which i will never do - or you could bolt it together properly. The glue allows time for alignment of the LED bead to the sweet spot. 1x 100 ohm pot, 3x AA rechargeable batteries, an Aluminium disc to cover the hole the lamp holder would go into, a copper washer as a heatsink and a metal angle bracket. The 110 ohm variable pot is the hardest to find and most expensive bit
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