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Re: Dark field illumination: Questions and answers

Posted: Fri Apr 24, 2020 1:17 am
by apochronaut
I'm not exactly sure of the era of the objectives, probably from about the first W.W. to the early 50's but the design is a split shroud, with a lens section below a knurled ring and a blank section with rear baffle only above it. You unthread the baffle section and replace it with the iris as an adjustable baffle.
The old ones were brass above and likely palladium plate below. In the 30's they changed to a shinier metal plate, for both sections. Maybe chrome but possibly some other non reactive metal.
I'm a bit busy for a few days but by Sunday I can probably take a couple of pictures of one. I may have both types. Send me a p.m. early in the week and jog my memory, if I don't get it done. Planting, these days.

Re: Dark field illumination: Questions and answers

Posted: Fri Apr 24, 2020 1:18 am
by apochronaut
The iris works on any of the higher N.A. objectives above anout 60X.

Re: Dark field illumination: Questions and answers

Posted: Fri Apr 24, 2020 4:47 am
by Bryan
apochronaut wrote:
Fri Apr 24, 2020 1:17 am
I'm not exactly sure of the era of the objectives, probably from about the first W.W. to the early 50's but the design is a split shroud, with a lens section below a knurled ring and a blank section with rear baffle only above it. You unthread the baffle section and replace it with the iris as an adjustable baffle.
The old ones were brass above and likely palladium plate below. In the 30's they changed to a shinier metal plate, for both sections. Maybe chrome but possibly some other non reactive metal.
I'm a bit busy for a few days but by Sunday I can probably take a couple of pictures of one. I may have both types. Send me a p.m. early in the week and jog my memory, if I don't get it done. Planting, these days.
Thanks for that, I found some examples what you’re talking about online.

Re: Dark field illumination: Questions and answers

Posted: Tue Apr 28, 2020 1:37 pm
by apochronaut
Here are some photos, as well.

Re: Dark field illumination: Questions and answers

Posted: Wed Apr 29, 2020 3:54 am
by Bryan
apochronaut wrote:
Tue Apr 28, 2020 1:37 pm
Here are some photos, as well.
Thanks for getting back to me on that, I’m watching a few on the evil auction site.

Re: Dark field illumination: Questions and answers

Posted: Wed Apr 29, 2020 11:16 am
by apochronaut
There are usually subtle changes in the objectives made between about 1910 and 1960, even though the actual optical designs varied little. Mostly, the advent of anti-reflection coatings and very minor changes to internal design of the barrel reduced flare a little and increased contrast. If I had a choice, I would probably aim for a silver barreled one, from the 40's or 50's but even the early Leitz objectives I have tried out are very good.