Totally not micrometeorites

Images made through a microscope. All subject types.

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Bob-O-Rama
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Totally not micrometeorites

Post by Bob-O-Rama »

Hi,

I've been accumulating subjects for the long boring winter. One thing I have wanted to find is micrometeorites. I have been collecting materials from the rooftops to process over winter. To see if the samples collected had anything at all in them, I checked for metallic spheroids ( usually perfectly round, with a crackle finish ) that are produced by human activity. Under coaxial illumination they look like a pyrite planet.

Image

This "death star" one is sort of nice.

Image

I have a number of lighting challenges. I'm using coaxial lighting because of the short working distance for my 20x objective. But as these are tiny spheres, the edges are not illuminated properly. I'm not sure what the proper lighting setup is for this - let alone what I can rig for $0 in my basement. This one, about 0.5mm in diameter, has a baby one magnetically attached to it at about high noon. To keep them from rolling away, ( no, I'm not kidding, they just roll away if you look at them wrong ) they are stuck to a tape coated magnet. The baby one is very tiny and almost perfectly spherical without any texture.

Image

While not "the real deal" they are interesting to me at least - like snowflake photography - and also they are in keeping with my "little planets" stereographic photos which have a similar vibe to them.

PeteM
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Re: Totally not micrometeorites

Post by PeteM »

Interesting images, Bob. Do you know how they're produced? Byproducts of coal power generation?? Or ???

Bob-O-Rama
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Re: Totally not micrometeorites

Post by Bob-O-Rama »

Fireworks, abrasive cutoff wheels, even a Bic lighter, anything that produces a shower of sparks. They are not present in remote areas or arctic ice, etc. I just found out we have an analytical X-ray florescence spectrometer, so I may be able to figure out what these are, and also test any suspect actual MM's. I just don't know the minimum sample size, some can do milligram sized samples. We have a SEM, which can also have sensors to do a similar sampling, however we don't have that probe.

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Re: Totally not micrometeorites

Post by rjlittlefield »

Bob-O-Rama wrote:
Mon Dec 05, 2022 1:20 pm
I'm using coaxial lighting because of the short working distance for my 20x objective. But as these are tiny spheres, the edges are not illuminated properly. I'm not sure what the proper lighting setup is for this - let alone what I can rig for $0 in my basement.
I suggest to surround the objective with a cylinder of diffusion material that goes all the way down to the tape that the spheres are mounted on. Illuminate the diffusion material with bright lights, and adjust the intensity or distance from the diffuser so as to balance this from-the-side illumination with the coaxial lighting that you're using now.

This will not give perfectly even illumination, but it will add a ring of bright reflection about half-way from center to edge. Beyond that, the spherical shape will be mostly reflecting the tape background, so that area is going to stay dark and bluish.

The only way I know to evenly illuminate a spherical subject is to suspend it in a spherical diffuser that wraps around the back side also. That seems not very practical for subjects like this.

--Rik

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Re: Totally not micrometeorites

Post by Bob-O-Rama »

rjlittlefield wrote:
Mon Dec 05, 2022 2:54 pm

I suggest to surround the objective with a cylinder of diffusion material that goes all the way down to the tape that the spheres are mounted on. Illuminate the diffusion material with bright lights, and adjust the intensity or distance from the diffuser so as to balance this from-the-side illumination with the coaxial lighting that you're using now. ...
That is challenging with a 1mm working distance, in the last I have used a thin piece of styrofoam from an egg container and cut a tiny donut out of it. I'll give it a try with this. Same for a donut shaped piece of memory foam, the business end of the objective can "squish" the foam. That's a great suggestion.

Scarodactyl
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Re: Totally not micrometeorites

Post by Scarodactyl »

Which 20x are you using? A fiber illuminator should be able to pump some light in from the sides even with diffusion but it is tricky with 1mm.

Bob-O-Rama
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Re: Totally not micrometeorites

Post by Bob-O-Rama »

Scarodactyl wrote:
Tue Dec 06, 2022 12:13 pm
Which 20x are you using? A fiber illuminator should be able to pump some light in from the sides even with diffusion but it is tricky with 1mm.
Nikon 20x 0.75 NA - I'm using it without cover glass, but compensating somewhat with the tube lens. ( I don't get as good a result with my Mitutoyo 20x ULWD one with side illumination. ) Please don't laugh:

Image

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Re: Totally not micrometeorites

Post by rjlittlefield »

Bob-O-Rama wrote:
Tue Dec 06, 2022 12:04 pm
rjlittlefield wrote:
Mon Dec 05, 2022 2:54 pm
I suggest to surround the objective with a cylinder of diffusion material that goes all the way down to the tape that the spheres are mounted on.
That is challenging with a 1mm working distance, in the last I have used a thin piece of styrofoam from an egg container and cut a tiny donut out of it. I'll give it a try with this. Same for a donut shaped piece of memory foam, the business end of the objective can "squish" the foam. That's a great suggestion.
There is no need for the diffuser to fit in any space under the objective. Just wrap it entirely around the objective and let it slide clear down so it rests on the tape with the subject. I do this routinely in special cases where the usual hemisphere diffuser would be awkward for some reason.

--Rik

Scarodactyl
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Re: Totally not micrometeorites

Post by Scarodactyl »

I have used oblique illumination with the Nikon 20xes, and it does work though it's fiddly. You might need to get the diffusion material fairly close to the subject for it to be bright enough. When you say ULWD 20x do you mean a normal 20x/0.42 or a sl 20x/0.28? The nikon can definitely outresolve either, but I think a 20x/0.42 might do better overall. For whatever reason I have noticed spherical aberration tends to be much less pronounced on coaxially illuminated subjects--you might notice the top is pretty crisp but the sides with more oblique light are smearier, and I suspect that will be more of a limitation than just getting light on it. Your results are really nice though! I've been meaning to find some of these after reading In Search of Stardust but hadn't gotten to it, maybe I need to bump it up the list.

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