Trying out a reflex objective lens

[Macro_Cosmos]

I obtained a Reflex objective lens, made by Edmund Optics. It is an infinity corrected objective lens, requiring a tube lens.

The lens is quite fat, I don't have any diffusers designed for such a fat lens. I used the one I made for lower mag, giving quite poor results.

It also seems like either ZS struggles with stacking due to the weird OOF elements, or my lighting is just rubbish. I'm leaning towards the latter here, the lighting is rubbish.

The lens is short and stubby. It's very very light weight as there's no optics involved.



So why reflex? Well for starters, there's theoretically no chromatic aberration, which is demonstrated by some boring test target shoots I did. I can't see any CA. Reflex lenses can also be coated for a broadband spectrum. The one I have is coated for 200-11,000nm, which covers UV all the way into IR, this isn't seen in ordinary objective lenses. A lens like this can open up to interesting subjects. I don't have a full spectrum consumer camera. Scientific ones are a pain to set up (I'm too lazy to figure it out), it's far easier to just get a used FX camera converted.

Here's the specs: https://www.edmundoptics.com/p/infinite ... flx/16543/
It is a 15x lens with an NA of 0.28. Pretty mediocre spec-wise. The Mit 10x has an NA of 0.28 and 20x would be 0.42, normal versions that is.

Single frame, highlights suppressed in post.


The lens does cover FX, but the corners aren't too good. The camera's auto white balance is all over the place, had to preset it. Usually the auto-WB is somewhat close.

Here's stacked, Pmax:

Pretty good resolution actually. The corners aren't great and there's some flare which I need to figure out a fix for. The flare might be inherent. My tubes are flocked and everything, no problems with glass based objectives.

Dmap looks nicer. I usually prefer the pmax looks.


OOF doughnuts!!


I need to get everything figured before concluding. My lighting is bad, which I will make a new diffuser for the stubby.
My adaption method is horrendous as well. I don't actually have a way to adapt the RMS objective to my tube lens that has M72 threads. All I did was use a thorlabs SM1-RMS and twisted the SM1 side (~M26) into the M26x0.75 female threads of the tube lens. I am seeing signs of misalignment, the top side of the frame is considerably sharper than the bottom side. I'm going to order a M72-RMS adapter first. The lens is purchased new, so it being damaged shouldn't be the case.
I plan on combating the glare issue via some sort of concentric baffle for the tube lens, it's quite large so that could be the issue from experience. I might give this objective another go later using the ITL200 thorlabs tube lens.

[rjlittlefield]

Interesting test results.

I tried out a used old-style Beck/Ealing 15X back in 2007 when I was attracted by the long working distance and lack of CA. But the experience was so painful and unproductive due to glare and weird warping effects on focus change that after many hours of failure I simply returned the objective, one of the very few times I've done that.

With the benefit of hindsight, I now suspect that the weird warping was due to what we now call a "utilized aperture effect", caused by highly directional oblique illumination with a shiny subject (moth wing scales).

But the glare problem was a matter of geometry. There seemed to be paths for light from outside the field to slip past the mirrors and get to the sensor or at least into the tubes undeflected. It would have worked OK with transmitted illumination and a field stop. But with an unrestricted field I couldn't figure out how to cut the glare enough to live with.

The design diagrammed at Edmund looks better than what I had. I'm pretty sure that mine did not have that long inner tube that blocks off-axis light. But in their diagram I still see paths for incoming undeflected light to glance off the inside of that inner tube. A look through the objective without the tube lens might reveal what's happening.

BTW, check your PM's, please. My outbox is showing one to you from back on Dec 2 still hanging around unread.

--Rik

[Pau]

It's very very light weight as there's no optics involved.

well, mirrors are optics in the same sense that lenses are. As you know for sure, most telescopes are mirror based.

[enricosavazzi]

[...]
But in their diagram I still see paths for incoming undeflected light to glance off the inside of that inner tube.
[...]

Unfortunately, my impression is that the catadioptric design may inherently have this problem, at least when the lens/objective is designed with a reasonable length-to-height ratio and covers a reasonably wide field on the image side. Since light passes three times in the same, or very close, positions in a ring-shaped volume near the center of the barrel, coaxial baffles mounted around the hole in the primary mirror and around the perimeter of the secondary mirror cannot completely prevent this problem without introducing a lot of vignetting.

[elf]

But the first single image is a nice photograph

[Macro_Cosmos]

It's very very light weight as there's no optics involved.

well, mirrors are optics in the same sense that lenses are. As you know for sure, most telescopes are mirror based.

Yep, that's right.
I should have said "optical glass".

[ray_parkhurst]

The 36x Beck lens I purchased at the surplus sale has a front "nosepiece" which reduces the stray light and greatly improves contrast. I subsequently purchased a 15x, which is of the same design as the EO lens you have, but it did not come with the nosepiece. I don't see one on yours either. I tried to make a nosepiece similar to the 36x but with longer snoot and larger aperture, and it did improve the contrast. The length and aperture seem very critical to ensure good performance, and I planned to optimize the nosepiece, but I ran into the strange stacking problems that seem to be inherent with this design. Single images are really nice, with no CAs and with high contrast and good coverage (with a proper nosepiece), but stacking creates weird artifacts even with the nosepiece in place. I still have the lenses, but am not sure how best to utilize them.

[Lou Jost]

I also was tempted by these reflex objectives and bought a massive Zeiss version, much larger than a Mitu, with two adjusting rings that I can't figure out. I think maybe it is not a pure mirror design.

[Lou Jost]

Here's an ingenious use of mirror objectives:

http://www.luminance-contrast.com/Mirro ... tives.html

Not too practical for our normal subjects, but clever.

[ray_parkhurst]

Here's an ingenious use of mirror objectives:

http://www.luminance-contrast.com/Mirro ... tives.html

Not too practical for our normal subjects, but clever.

You can see the front aperture in the diagram. As you can see, the aperture is just larger in diameter from the front mirror. Without the nosepiece, there is indeed an aperture, but it is much larger than the front mirror, and nearly in the same plane.

[Pau]

I never heard about luminance-contrast, but after taking a look at their image gallery I think that I understand why.

[Lou Jost]

Yep, definitely a specialized field