Questions about the use of an eyepiece as a photo projection lens

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gekko
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Questions about the use of an eyepiece as a photo projection lens

#1 Post by gekko » Mon Dec 19, 2016 2:49 pm

This question arose in my mind when reading the discussion about using a projection lens with Rod's AO microscope ( viewtopic.php?f=24&t=776 ). I had always assumed, without real knowledge, that in the case of microscopes that require compensating eyepieces (especially with high power or with highly corrected objectives), a proper compensating eyepiece raised a few mm in the phototube would act as a good projection lens (for direct projection onto a camera sensor), and that this would be preferable to a generic, non-compensating projection lens. My questions are:
(1) Is that true? And to what extent?
(2) Would the image quality deteriorate as the eyepiece is raised further in the phototube (to project a smaller image to match the size of the camera sensor), since it would be farther from the point where it was designed to be used (i.e. fully seated to provide a virtual image)?
Many thanks!

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75RR
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Re: Questions about the use of an eyepiece as a photo projection lens

#2 Post by 75RR » Mon Dec 19, 2016 6:53 pm

Hi gekko

A: to 1) Yes, they do work and work very well. It is what I have been using for a long time now, ever since I cobbled together a trinocular.
David Walker uses or at least used to use one that I know of, and Charles Krebs mentions their use in his how to manuals.
I have recently started experimenting with a Projektiv f=63mm, so far all I can really say is that the Projektiv f=63mm is more convenient.
I haven't decided yet which is better.

A: to 2) I would raise and lower the eyepiece from 10mm up to 17.5mm (had some spacers made up from plastic tubing in 2.5mm increments) in order to vary the area of the field of view that was to be captured and did not notice any degradation within that range.
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

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gekko
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Re: Questions about the use of an eyepiece as a photo projection lens

#3 Post by gekko » Mon Dec 19, 2016 11:14 pm

Thank you 75RR for your reply. Yes I know they work well but I was wondering (1) how they compare to generic projection lenses and whether they may be as good as the manufacturer's own compensating projection lenses and (2) whether their performance (image quality) deteriorates in theory as they are raised more, and hence further away from their design (fully seated) position. You did say you didn't notice a difference in the image quality as you raised it, but the degradation in quality may be too slight to easily observe. Thanks again.

JimT
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Re: Questions about the use of an eyepiece as a photo projection lens

#4 Post by JimT » Tue Dec 20, 2016 11:59 pm

Gekko, I am not sure this directly answers your question but before I bought my Amscope trinocular upgrade I used eyepiece projection with my camera on a tripod, extension tubes, and a hollowed out “Plug: to encircle the eyepiece. Very effective. Only reason I went to the trinocular was convenice.

Eyepiece projection is a very effective way to achieve stellar images in astronomy imaging and also microphotragraphy.

JimT

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