episcopic adapter

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soldevilla
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episcopic adapter

Post by soldevilla »

I have no experience in this. I want to do some photography tests using incident light, that is, a beam splitter that sends the light through the optics of the microscope objective, and that light reflected from the object goes back through the beam splitter to go to the camera. I am writing this because I have seen lenses that have a conduit for light around the lenses like a small ring illuminator, and that does not work for me.

Is there a module that can be attached to a modular system like the ones we use? that is, not a complete microscope, but an objective, some extension tubes and the camera, all organized on a guide support with a stepper motor.

And one last question. Isn't this system extremely sensitive to loss of contrast and reflections in the image?

Thank you

Pau
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Re: episcopic adapter

Post by Pau »

Beginning from the end,
And one last question. Isn't this system extremely sensitive to loss of contrast and reflections in the image?
Yes, it is, due to reflections both on the subject surface and on the objective lens elements.
In many cases this kind of systems use crossed polarizers, a polarizer between the light source and the beamsplitter and an analizer between the BS and the sensor.
To avoid objective internal reflections often you can see a rotatable 1/4 wave plate between the objective and the sample ("antiflex" in Zeiss naming)

Likely Thorlabs and similar Optics big names could have the kind of device you want, although I guess much less expensive adapting a microscope epiiluminator for the task (even more when mastering 3D printing :D )
Pau

soldevilla
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Re: episcopic adapter

Post by soldevilla »

Oh! Thanks, Pau. I go to try find something in internet...

Scarodactyl
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Re: episcopic adapter

Post by Scarodactyl »

It does seem that the quarter wave plate under the objective is only needed at lower magnifications. It's essential for stereos and macroscopes, and strongly recommended for the mitutoyo 2x objective (the 1x I think they suggest a whole polarizer?) But 5x and up it isn't really an issue. Maybe that's more a factor in modern objective design generally.

Lou Jost
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Re: episcopic adapter

Post by Lou Jost »

The very cheapest way to do this is to buy an epi-illuminator and integrate this into the space bertween the objective and sensor (or tube lens). This can cost as little as $35 (one now available at that price on eBay). I also bought a second, cheaper, simpler epi-illuminator for the same microscope (Nikon Optiphot), which I cannibalized for its connectors. One of these connectors can be modified to hold a microscope objective adapter, and the other can be modified to take a camera or tube lens. You don't actually need the micrscope for this; in fact, it works better without a microscope. I have a vertical system and this illuminator sits on it directly.

This can also be used for a "poor man's fluorescence" adapter, with the addition of some filters. A dichroic mirror is not needed if your UV light source is strong enough.

Scarodactyl
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Re: episcopic adapter

Post by Scarodactyl »

Make sure when getting a Nikon one that you check that it has both a polarizer and an analyzer before you buy. Some of them don't have a separate polarizer slot so I assume a polarizer is more permanently installed, but these are often stripped out. The rotatable polarizer with a slot for a quarter wave plate tends to be much rarer and more expensive since you can use it for epi DIC, but if you can get it or DIY it it's worthwhile to have that extra degree of control.

Chris S.
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Re: episcopic adapter

Post by Chris S. »

I started on a similar project last winter, using an Edmund Optics plate beam splitter and mounting cube. Integration should be pretty easy, but I got sidetracked onto other projects and the parts still wait on my work table.

--Chris S.

soldevilla
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Re: episcopic adapter

Post by soldevilla »

Well, I already returned home and the beamsplitter and illuminator had already arrived from China. I spent one day printing the adapters (well, the printer, I did other things in the meantime) and another afternoon lining the interior of the entire system with black velvet, because as I was afraid, this type of lighting is extremely sensitive to stray light. . Now I have no visible reflections, but the rear element of the lens is a real mirror! With a x20 the image, properly treated, could be usable. With the x10 there is too much stray light, with the x5 I hardly see the image that the lens projects and with a small, cheap and good Rodenstock that was talked about here a while ago, I directly see nothing more than a veil of light.

I need to work on those reflexes. I can use my telescope polarizers (a bad buy left in a drawer) but I need some information on that. Can someone suggest a link where to read a little about this? My training is not optical, and those 1/4-wave retarder terms sound very strange to me.

This is an exciting world to try

soldevilla
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Re: episcopic adapter

Post by soldevilla »

Update:

I have finished designing and printing the components for the incident light adapter. It's quite a few pieces with some fine threads so it took me a bit of time. The design includes a 1.25 "polarizer from my telescope on top of the beamsplitter (inside the gray piece) and another polarizer (which I can rotate with the red knob) inside the group of gray pieces on the illuminator.

I have also printed a thread adapter from the Rodenstock lens to the beamsplitter, but even though I can see an image now, it still has too much stray light. On the other hand, the x4 is already perfectly usable and if I increase it to x10 or x20, it gets better and better.

I show the first test. Objective x4 and a stone that I have recovered from the trash can, with a small hole with crystals. Miracles never happen, and the color temperatures of the LEDs could not be more different, but in this case it helps me to show how the incident light (green) penetrates to the bottom of the geode.

I do not know the performance of a commercial microscope with this lighting and I am sure it is very superior, but I am very happy.
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Scarodactyl
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Re: episcopic adapter

Post by Scarodactyl »

This type of illumination will never give great results on very 3d subjects. You'd want to try with something flat and reflective like a wafer or crystal face to have a better idea.

Pau
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Re: episcopic adapter

Post by Pau »

Can someone suggest a link where to read a little about this? My training is not optical, and those 1/4-wave retarder terms sound very strange to me.
This is a good source (although you likely already know it)
http://zeiss-campus.magnet.fsu.edu/arti ... ected.html

Very interesting device! I admire your making skills.

Does your epi-illumination cover all the field? Do you use any wind of collimating optics?
Pau

soldevilla
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Re: episcopic adapter

Post by soldevilla »

Does your epi-illumination cover all the field? Do you use any wind of collimating optics?

... no... I have tested it only with the x4, that is not the best objective for this use. And I not used a small chip camera attached to a microscope, but a APS Canon body. Next test will be with my astronomical camera and the x10. Lets go...

Pau
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Re: episcopic adapter

Post by Pau »

I have tested it only with the x4, that is not the best objective for this use.
Sure, at least in general it would be more flare prone than higher mag. ones, but because the objective is also acting as condenser the visual or camera sensor coverage can be pretty similar (being the actual illuminated subject field smaller, of course)

In my opinion if your optical systems has good coverage for a given sensor with incident diffuse illumination it should also more or less do with an episcopic illuminator with the right light collimating optics.
Pau

rjlittlefield
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Re: episcopic adapter

Post by rjlittlefield »

Pau wrote:
Mon Jul 05, 2021 7:21 am
with the right light collimating optics
I see in the image that there is a bright circular area surrounded by dark. Initially I had assumed that this represented the structure of the stone, but now it occurs to me that illumination light may not be reaching the edges of the field. That could be determined by photographing a flat uniform subject, like a piece of paper.

If the problem is uneven illumination, then I think the solution is less collimation, not more. To fully illuminate the subject area seen by the sensor, illumination light must enter the beamsplitter over the same range of angles that the objective will produce to form the image.

The limiting bad case is when light enters the beamsplitter at only one angle, in which case the objective focuses all of it onto a single point on the subject. This can be understood as just the reverse of the usual imaging process, in which the objective collects light from a single point on the subject and sends it through the infinity space as a beam of parallel rays, all at the same angle.

--Rik

Pau
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Re: episcopic adapter

Post by Pau »

To be more exact, the "epicondenser"* optics must focus the light source at the objective rear focal plane and fulfilling it, like in transmitted Köhler

* this is the usual name although the main condenser in this case is the objective itself
Pau

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