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General question about lighting - Pseudo Koehler
Posted: Sat Oct 23, 2021 8:54 am
by smollerthings
Hi All,
So I see people talking about pseudo Koehler. What does it mean? Does it mean collector lens without the iris?
Thanks
Re: General question about lighting - Pseudo Koehler
Posted: Sat Oct 23, 2021 11:24 pm
by dtsh
I don't know what pseudo koehler is, but modified Koehler usually involves a frosted lens just after the bulb. You get the even illumination and still get the rest of koehler (field iris, etc).
Re: General question about lighting - Pseudo Koehler
Posted: Sat Oct 23, 2021 11:38 pm
by Dubious
Just semantics, but I would consider pseudo-Koehler to be any fixed system for providing a reasonable facsimile of Koehler illumination for most purposes; so yes, generally a lens but no adjustable field diaphragm.
Re: General question about lighting - Pseudo Koehler
Posted: Sun Oct 24, 2021 12:56 am
by Greg Howald
I put an iris diaphragm centered directly on top of the illuminator and I get results similar to Koehler lighting. If there is very short distance between illuminator and condenser it won't work. It's a trial and error thing, but when it works it does a fair job.
Re: General question about lighting - Pseudo Koehler
Posted: Sun Oct 24, 2021 9:22 am
by smollerthings
Thanks all. I think it is indeed frosted glass + collector without field diaphragm.
I found a nice video on the subject that helped me on the matter.
Re: General question about lighting - Pseudo Koehler
Posted: Wed Nov 03, 2021 10:07 pm
by linuxusr
I can tell you that "pseudo-Koehler" illumination is not a misnomer as I almost fell victim to buying a scope that was not "full" Koehler but rather "simple" Koehler. The fact that some scopes are advertised as "full" Koehler indicates that some scopes are less than "Koehler." If they are < Koehler they are not Koehler.
Any tutorials that you find--and sorry I can't quote one at this moment-- tell you that what you need for bona fide Koehler illumination setup are three things:
1. A condenser lens that you can move in the Z direction,
2. Two condenser lens centering screws,
3. A field lens diaphragm.
If you have those components, you have the capacity for Koehler illumination. If you do not have those components, you do not have Koehler illumination.
Re: General question about lighting - Pseudo Koehler
Posted: Mon Nov 08, 2021 2:12 pm
by linuxusr
linuxusr wrote: ↑Wed Nov 03, 2021 10:07 pm
I can tell you that "pseudo-Koehler" illumination is not a misnomer as I almost fell victim to buying a scope that was not "full" Koehler but rather "simple" Koehler. The fact that some scopes are advertised as "full" Koehler indicates that some scopes are less than "Koehler." If they are < Koehler they are not Koehler.
Any tutorials that you find--and sorry I can't quote one at this moment-- tell you that what you need for bona fide Koehler illumination setup are three things:
1. A condenser lens that you can move in the Z direction,
2. Two condenser lens centering screws,
3. A field lens diaphragm.
If you have those components, you have the capacity for Koehler illumination. If you do not have those components, you do not have Koehler illumination.
Another step in completing the Koehler illumination setup is pulling one ocular, looking down the eyetube, and adjusting the Abbe condenser aperture. This can be more precisely accomplished with a centering telescope, so you could add that as an optional feature.