Mirau objective?

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Smokedaddy
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Post by Smokedaddy »

Thanks Mike.

iconoclastica
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Post by iconoclastica »

OK, now we're talking business. First I changed for an object to a razor blade. That made a difference indeed. The flat surface displayed moving colour bands. Not nice rings, but I guess the surface is too rough for that. Here it is, colours exaggerated in photoshop:

Image

Then I moved to the slanted surface of the cutting edge. Moving about as I turned the focus I could see a band of interference pattern. With very little contrast, so I had to push it in Photoshop again to make it visible:

Image

Then I read Mike's explanation (thank you, Mike!). I was lucky to have just the right epi-illuminator, even though still powered by an uncollimated torch. Nevertheless, the interference patterns became much more prominent. The photo of the flat-surface colours almost as clear as the edited one above. The sloped pattern I show (cropped, but unedited) here:

Image

Very interesting to have tried this, but I don't see how it would be of any use to me, especially as it is limited to reflective surfaces (is it?).
--- felix filicis ---

mtuell
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Post by mtuell »

Well, everything is reflective - the best AR coatings still aren't perfect. But, I think you mean highly reflective? No, it works fine on bare glass which is about 4% reflective. The contrast of the fringes will vary with the ratio of test beam to reference beam, so you will see changes in contrast with changes is material reflectivity.

One of the primary limitations is the form of the object. If it varies from flat by very much, this technique isn't very useful without the scanning system which combines fringe data with known stage motion data. Looking at a bug eye, for example, the individual eye parts are too highly curved to do much with interferometry, since you lose fringes (both from high slopes and coherence length issues if you aren't monochromatic).

It is mostly used to inspect glass and silicon substrates and as James showed, you can get some interesting pictures on ICs or camera sensors. But, overall, things have to be fairly flat for anything interesting to happen.

Mike

Macrero
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Post by Macrero »

Note that this objective is intended for Contact Interometry. The MI multiple beam (Tolansky) objectives utilize a reference mirror which must be brought into direct contact with the specimen. Nikon dixit.

I can't see any usefulness of this objective outside of what it is intended for (and used as intended).

Btw, objective is rare, thought not "that" expensive compared with the "regular" M Plan. $752 vs $953 (the MI) original list prices. For instance, the M Plan 20/0.4 LWD was $1.108 and the ELWD - $1.145.

Best,

- Macrero

Edit: Sorry, I'm multitasking and I didn't read the thread... I just realized your objective is DI (non contact). I still can't see much of worthwhile use for it on camera, though. Also, the DI has a very short WD - 1.9mm.
https://500px.com/macrero - Amateurs worry about equipment, Pros worry about money, Masters worry about Light

mtuell
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Post by mtuell »

Yes, the MI is a different beast. The DI is very useful for what it is intended for, but not so much outside of that. If you were making knives or razor blades or optical surfaces or semiconductor wafers - it gives a way to visualize the surface in (essentially) 3D, so you can know it is good or that it needs improvement. It isn't really meant for simply making pretty pictures, but in certain circumstances (like James' video), it can do that. It really isn't meant for extreme macro applications.

Mike

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