Finding the subject - ideas needed

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nielsgeode
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Finding the subject - ideas needed

Post by nielsgeode »

I photograph crystals (minerals) at high magnification with microscope lenses. Because the specimen can be large (2, 3, 4, ... cm) and the crystal on it small (< 1mm) it can be a challenge to find the subject due to the small field of view of a 20x lens.

In the past I used a dSLR and used a small flashlight to shine through the viewfinder to get a spot of light when the subject is in focus. Then if you know where on the piece the crystal is, you can move your piece and easily find the subject.
Now with mirrorless this is no longer possible because the viewfinder is just a small LCD.

It's a bit of a long shot, but who has a creative idea to get a beam of light out of your objective so it focuses to a spot at the focal point? It would make life much easier for me. Or another creative idea, like projecting a grid on the specimen that you can use to find your crystal? Ideally a color gradient grid so you know where you are :D

Love to hear crazy ideas :D

CrispyBee
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Re: Finding the subject - ideas needed

Post by CrispyBee »

You could go the other way around and use a laser pointer to highlight the crystal you want to shoot. Then move the camera until it's in the FOV, should be easily visible even when it's way out of focus.

EDIT: or - if your lens is mounted on bellows or tubes which are connected to a rail you could unmount the camera and still use the same technique of shining a light behind the lens to align the subject.

Lou Jost
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Re: Finding the subject - ideas needed

Post by Lou Jost »

CrispyBee wrote:
Thu Jan 09, 2025 2:13 pm
You could go the other way around and use a laser pointer to highlight the crystal you want to shoot. Then move the camera until it's in the FOV, should be easily visible even when it's way out of focus.

EDIT: or - if your lens is mounted on bellows or tubes which are connected to a rail you could unmount the camera and still use the same technique of shining a light behind the lens to align the subject.

Or have the laser mounted on the focusing stage, so the camera can remain stationary.

CrispyBee
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Re: Finding the subject - ideas needed

Post by CrispyBee »

Lou Jost wrote:
Thu Jan 09, 2025 2:24 pm
CrispyBee wrote:
Thu Jan 09, 2025 2:13 pm
You could go the other way around and use a laser pointer to highlight the crystal you want to shoot. Then move the camera until it's in the FOV, should be easily visible even when it's way out of focus.

EDIT: or - if your lens is mounted on bellows or tubes which are connected to a rail you could unmount the camera and still use the same technique of shining a light behind the lens to align the subject.

Or have the laser mounted on the focusing stage, so the camera can remain stationary.
Oh you mean like a red dot sight like an archetypical sniper in a movie? That's an interesting idea! :D

rjlittlefield
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Re: Finding the subject - ideas needed

Post by rjlittlefield »

nielsgeode wrote:
Thu Jan 09, 2025 2:07 pm
who has a creative idea to get a beam of light out of your objective so it focuses to a spot at the focal point?
I suggest to stick a beamsplitter behind the objective.

Shine a flashlight in from the side for subject finding; block that path for photographing.

I'd start with a simple piece of uncoated glass as a beamsplitter, something like a piece of microscope slide or cover glass.

--Rik

nielsgeode
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Re: Finding the subject - ideas needed

Post by nielsgeode »

rjlittlefield wrote:
Thu Jan 09, 2025 2:37 pm
nielsgeode wrote:
Thu Jan 09, 2025 2:07 pm
who has a creative idea to get a beam of light out of your objective so it focuses to a spot at the focal point?
I suggest to stick a beamsplitter behind the objective.

Shine a flashlight in from the side for subject finding; block that path for photographing.

I'd start with a simple piece of uncoated glass as a beamsplitter, something like a piece of microscope slide or cover glass.

--Rik
Can you explain it in a bit more detail? I don't see how I can get the beam splitter behind the lens without creating massive gaps where light can enter.

Pau
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Re: Finding the subject - ideas needed

Post by Pau »

The easier approach would be to place a microscope epiiluminator, it is designed for a somewhat similar function
Pau

Beatsy
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Re: Finding the subject - ideas needed

Post by Beatsy »

You mention using microscope objectives - plural. Could you align your subject to put it in the middle of the frame using a lower power lens first (say 2-5x)? Then back off the camera (assuming you're using a rail of some sort), swap in the 20x, and move forward to re-acquire focus.

Cheers
Beats

rjlittlefield
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Re: Finding the subject - ideas needed

Post by rjlittlefield »

nielsgeode wrote:
Thu Jan 09, 2025 3:06 pm
Can you explain it in a bit more detail? I don't see how I can get the beam splitter behind the lens without creating massive gaps where light can enter.
My plan was to mount mine inside an extension tube with a hole bored in its side for the external light to shine through.

But I never went to the trouble of putting that together.

Instead I've used the strategy mentioned by Beatsy: start at low mag and work toward higher. That approach also provides an opportunity to plan best framing for the high mag shots.

--Rik

Ebi
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Re: Finding the subject - ideas needed

Post by Ebi »

I'd avoid a beamsplitter as it migth reduce the image quality. What about two low powered lasers angled in from the side, so that they meet at parfocal distance? That way you get a marker for alignment without any objects in your beampath.
For reference, this is the same concept many laser markers use to set the correct distance from the F-theta lens.

Scarodactyl
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Re: Finding the subject - ideas needed

Post by Scarodactyl »

Beamsplitters typically don't affect image quality noticeably if they're in infinity space, though adding extra infinity space can reduce sensor coverage.

iconoclastica
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Re: Finding the subject - ideas needed

Post by iconoclastica »

The beamsplitter's R/T ration does not need to be 50/50 but can pass more of the light to the camera.
A microscope epi-illuminator is the easy solution in the studio, but top heavy in a moblile setup. A 3D printed cube with 45 degree edge to glue on the beamsplitter, and ends that enable extension rings to be attached, will be incomparably much lighter. (It's just like a larger size fluorescence filter cube). Printing in parts may prove to be easier than making a monolith.
--- felix filicis ---

JW
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Re: Finding the subject - ideas needed

Post by JW »

I find that strategically placing arrows often helps to point the way to the subject.
xpic.jpg
It's not what you look at that matters, it's what you see - Henry David Thoreau

colohank
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Re: Finding the subject - ideas needed

Post by colohank »

I think an external aid, like JW's arrow, would be easier to use than trying to install a beam-splitter somewhere in the optical train. But I'd suggest a more linear pointer, like a thin sewing needle. Mount the specimen on a stage, preferably one with micrometer adjustments. Use a relatively low powered loupe to position the point of the needle directly over the subject crystal, relying on Blu-Tack or whatever* to fix the needle's position. It should be fairly easy to move the stage about until the any part of the needle shaft, whether in focus or not, is located in the viewfinder. Then, move the specimen incrementally such that the shaft remains in the field of view and until the point and the subject beneath are located. Once on target, remove the pointer, set focus parameters, and begin shooting.

*Instead of fussing with an in-line beam-splitter or Blu-Tack, devising an independent, XYZ adjustable mount for such a pointer, one which allows the pointer to be swung out of the way after the subject is located, might be a worthy project.

heartprairie
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Re: Finding the subject - ideas needed

Post by heartprairie »

You can get a beam splitter very cheaply from AliExpress. I have personally used the following parts:

"Half Reflection Half Transmission Lens Adapter for Monocular Coaxial Digital Microscope" (i.e. beam splitter)
https://www.aliexpress.com/item/32898574847.html

"Datyson Microscope Photography Accessory 30mm Interface to M42" (for coupling the beam splitter to your tube lens)
https://www.aliexpress.com/item/4001231388266.html

It comes with a standard M26 mount on the front for Mitutoyo-type objectives - the RMS variant just includes an adapter ring. Other types of adapter rings are available elsewhere.

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