relay lens: to use or not to use

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iconoclastica
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relay lens: to use or not to use

Post by iconoclastica »

I have just started in micro-photography, and there's some things that work fine but some other that I don't understand.

I understood there's two ways to take a photo through the microscope: project the primary image onto the sensor, and use projecting eye-pieces. The first option seemed the simplest, so I removed the phototube, added a dovetail connector, a helicoid for focusing, an appropriate length of extension tubes, and a M42 adapter ring and voila, it worked. Clear images with not too much CA and perfectly parfocal with the eye eyepieces. Only perfect centering is still an issue.

So why should anyone want to use projecting eye-pieces C-mounts, T-mounts and whatever to achieve the same result? From what I read - please correct my book wisdom with your practical knowledge - there's two reasons: the objectives need to be corrected (not so with Olympus and Nikon), or the image must be reduced to fit the camera sensor.

I am using a Canon APS-C (22mm) on a Nikon Labophot (23mm tubes), so I need neither and I already have the best setup???

Now this microscope, when I bought it, came with a coolpix screwed onto a Zeiss C5x eyepiece on a black 12cm Zeiss Opton phototube.
I tried the same thing with my Canon DSLR, a 28mm step-down ring on the 50mm lens. The result was much worse with heave CA, especially away from the centre. So that is obviously not the way to go.

I also happen to have two other eyepieces, that may be better suited for the job, a Nikon CF PL5x and a Nikon TV Relay lens 1x/16. I have not yet tried these for I still have to finish the physical fit to the camera.

I would be most interested to read your comments and, perhaps, explanations.

Wim
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enricosavazzi
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Post by enricosavazzi »

Direct projection from the objective (or tube lens in infinity corrected system), as you mention, works well if the objective, or objective + tube lens, are corrected and require no further correction by the eyepieces.

Another limitation of direct projection is the size of the image circle. It is usually the same as the field diameter of the eyepieces (for 10x eyepieces, this can be anywhere from 18 mm for legacy equipment to over 26 mm for ultra-wide modern systems like Olympus UIS2). The diameter of the image circle decides which sensor size you can use for direct projection on a given microscope system. In practice, direct projection works without vignetting for Micro 4/3 and sometimes APS-C, rarely for full-frame.

Another advantage of direct projection is that it is space-saving compared to eyepiece projection. The latter needs a tube above the eyepiece that increases the total height of the equipment by some 10-20 cm or more.

The advantages of using a projection eyepiece are that the eyepiece can provide any correction needed by the objective, and that by changing eyepiece you can cover different sensor sizes. Unfortunately, in legacy systems many projection eyepieces are designed for large format films, and projection eyepieces for small formats suitable to digital cameras can be scarce and expensive.

The third way to connect a camera to a microscope is by using an afocal setup, i.e. use a camera lens to "look" into an ordinary (not projection) eyepiece. This can also work well, and by changing the FL of the camera lens you can cover different sensor sizes. Depending on the eyepiece field size, a 50-60 mm lens is suitable for full-frame, about 45 mm for APS-C, and 30 mm for Micro 4/3. Vignetting can occur if the front element of the camera lens (or more precisely the entrance pupil of the lens) is too far from the eyepiece. Zoom lenses typically do not perform well in this setup. High-eyepoint ("glasses") eyepieces may work better than old-fashioned ones with small exit elements.

This bulletin board contains plenty of information about specific camera setups.

PS - The Nikon TV Relay lens 1x/16 you mention is likely a projection eyepiece. The term "relay lens", in general, means different things to different people and in different contexts, so it is not generally used if one wishes to be specific. In a general sense, a relay lens just gets light from one part of an optical device and forwards it to another part.
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viktor j nilsson
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Post by viktor j nilsson »

Also worth mentioning that your highly corrective Zeiss eyepiece is a very poor match to your Nikon objectives that are meant to be almost fully corrected on their own (I assume these are Nikon CF objectives). So I'm not at all surprised you get poor image quality when you combine them in a atocal setup. With a proper CFW eyepiece, the quality should be pretty good.

iconoclastica
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Post by iconoclastica »

Thank you, Enrico, for putting things into context. I think I mostly understand it now, especially after rereading some sections of your book that I skimmed over two years ago when this all was of no concern to me.

Today I made a provisional adapter out of rings of MDF to try both projection lenses. The CF 5x does not perform very well, but the TV relay lens 1x/16 seems to work marginally better than capturing a direct image. The contrast is less, but so is the CA. However, the DSLR is towering 27cm over the head, compared to 12 whith the direct image, so I'll concentrate on the latter for now.

I did not quite understand why (in fig 8.19) you remove parts from the trinoc head. Would this help me too?
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iconoclastica
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Post by iconoclastica »

viktor j nilsson wrote:Also worth mentioning that your highly corrective Zeiss eyepiece is a very poor match to your Nikon objectives that are meant to be almost fully corrected on their own (I assume these are Nikon CF objectives). So I'm not at all surprised you get poor image quality when you combine them in a atocal setup. With a proper CFW eyepiece, the quality should be pretty good.
I then wasn't much surprised by that result. But it was easy to try.
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ChrisR
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Post by ChrisR »

There IS a Nikon 2.5x CF projection eyepiece which would suit better than 5x. Only Olympus did a 1.6x, (corrective). :(

I remember someone using a tele-converter on a camera body to enlarge the direct-projection image, but I haven't tried it.
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Ichthyophthirius
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Post by Ichthyophthirius »

iconoclastica wrote:I did not quite understand why (in fig 8.19) you remove parts from the trinoc head. Would this help me too?
Hi,

Could you post a few images of your setup? This is hard to follow :wink:

In particular, how you manage a direct projection on a Labophot? The intermediate image is not accessible on the trinocular tube (unless you re-focus heavily).

Regards, Ichty

enricosavazzi
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Post by enricosavazzi »

ChrisR wrote:There IS a Nikon 2.5x CF projection eyepiece which would suit better than 5x. Only Olympus did a 1.6x, (corrective). :(
[...]
There is also the Olympus PE 2.5x for the UIS/UIS2 infinity system, which likewise is designed for completely corrected objectives and covers full frame (do not confuse with the Olympus FK 2.5x and NFK 2.5x photo eyepieces, which are part of the older finite system).

The barrel of the PE 2.5x has a non-standard diameter of 25 mm, however. It can be used in a 30 mm photo tube together with a custom-made adapter sleeve.
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enricosavazzi
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Post by enricosavazzi »

iconoclastica wrote:[...]
I did not quite understand why (in fig 8.19) you remove parts from the trinoc head. Would this help me too?
Not if you intend to use the trinocular head on a microscope. I removed the optics at the base of the head because I decided to use the head as a focuser for photomacrographic lenses, which do not expect any refractive optics between lens and sensor.

I believe in this case the modified trinocular head was originally from a finite microscope, so the lens I removed is not a tube lens (in the sense used for infinity corrected systems), although it sits in a similar place.
--ES

iconoclastica
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Post by iconoclastica »

Ichthyophthirius wrote: Could you post a few images of your setup? This is hard to follow :wink:

In particular, how you manage a direct projection on a Labophot? The intermediate image is not accessible on the trinocular tube (unless you re-focus heavily).

Regards, Ichty
OK, I'll try. These are both setups. The one on the left captures the intermediate image, the one on the right uses a projection lens.

Image
T1: tubus for direct image; T2: Zeiss photo tube (12cm, no optix but the projection lens; C: provisional coupler.

My self-constructed tube consists of four commonly available components. I determined the required length roughly by adding and removing various lengths of extension tubes, until the image came into focus. Then the helicoid allows for very precise focusing. It has not fixing screw, but it turns not too lightly:


Image

The other test setup is nothing special. Just the photo tube that I got with the microscope, that has been used with the Zeiss eye-piece and the Coolpix. Here I inserted the TV relay lens. On top of that come two glued together cylinders, of which the lower one fits the eyepiece (31.5mm) and the top one falls into that same extension tube:


Image


(The camera with the dangling strap is not the one I normally use, for that one I got in my hands to take the picture :wink: )
Last edited by iconoclastica on Fri Nov 16, 2018 1:51 pm, edited 1 time in total.
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iconoclastica
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Post by iconoclastica »

enricosavazzi wrote: I believe in this case the modified trinocular head was originally from a finite microscope, so the lens I removed is not a tube lens (in the sense used for infinity corrected systems), although it sits in a similar place.
Since my second binocular head can be added on top of the trinocular head, I expect that there be a lens to reset the tube length to 160mm, despithe the 60mm added by the trinocular head.
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iconoclastica
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Post by iconoclastica »

enricosavazzi wrote: There is also the Olympus PE 2.5x for the UIS/UIS2 infinity system, which likewise is designed for completely corrected objectives and covers full frame (do not confuse with the Olympus FK 2.5x and NFK 2.5x photo eyepieces, which are part of the older finite system).

The barrel of the PE 2.5x has a non-standard diameter of 25 mm, however. It can be used in a 30 mm photo tube together with a custom-made adapter sleeve.
Withe a dovetail adapter like this one you can easily build any length of tube. Next time I will try 49mm, for 48.5 is just a teemsy bit off centre.
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Ichthyophthirius
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Re: relay lens: to use or not to use

Post by Ichthyophthirius »

iconoclastica wrote: I am using a Canon APS-C (22mm) on a Nikon Labophot (23mm tubes), so I need neither and I already have the best setup???
Hi,

Thanks for posting the images. This is the discussion head; it's a bit unusual so it doesn't come up very often. It appears to effectively give access to the intermediate image which is great to know.

So if the image covers your APS-C sensor well (no vignetting) and you're using Nikon CF (Plan?) objectives, this is the best possible setup.

Plan and planapo objectives make the best use of this relatively large sensor area.

Sometimes it can be beneficial to add a field stop to exclude reflexions on the inside of the tube.

Is the tube factor 1x or 1.25x?

Regards, Ichty

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Post by ChrisR »

Optiphot/Labophot & similar scopes seem to come with quite a varity of trinoc tube lengths, some non removable. I have two which are long, but there's another which is not as short as the teaching/discussion head.
:-k :smt017
Anyone know the story??
Last edited by ChrisR on Fri Nov 16, 2018 4:11 pm, edited 1 time in total.
Chris R

iconoclastica
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Post by iconoclastica »

Yes, it is a discussion head. I thought it was the same as the trinocular head with the 3rd tube unscrewed (ok, and there's a movable arrow pointer)?

It nearly covers the sensor, only the very corners are black. The coverage by the 1x projection lens is a little less, but presumably thanks to its internal baffle, the cut off is sharper.

How do I determine the tube factor?
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