Mitutoyo 50x 0.55 and Mitutoyo 50x SL 0.42

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Munich
Posts: 28
Joined: Mon Jun 16, 2014 5:36 am

Mitutoyo 50x 0.55 and Mitutoyo 50x SL 0.42

Post by Munich »

Hello Everybody,
A couple of months ago, I bought a Mitutoyo 50x SL 0.42 on Ebay. The seller did not deliver for a month and I opened a case against him. While waiting, another Mitutoyo 50x surfaced, this time a regular one with a N.A. of 0.55. I had given up hope on my first purchase and bought that one too. Then, both lenses arrived within a short period of time.

I have no experience with this magnification and wonder whether one of the knowledgable forum members could kindly give a few ballpark remarks about the quality of the images below.

Both of them have been shot with an Olymps EM5 MKII, a Sigma 150mm 2.8 Macro as a tube lens and a Metz 54 at 1:256 power. In both cases, I took 10 shots of an old Zeiss Jena diffraction grating, selected the best one and cropped (100%). The images were shot as ORF files, converted to DNG with Lightroom and exported as JPEG. They are unsharpened und unmodified in any other way.

First the 50x SL 0.42

Image

Then the normal 50x with the larger N.A. of 0.55 and better sharpness and contrast.

Image

Is that roughly the resolution one should expect or is there something wrong with the lenses, my approach or my target?

Beatsy
Posts: 2105
Joined: Fri Jul 05, 2013 3:10 am
Location: Malvern, UK

Post by Beatsy »

I can't offer any judgement on the first one, but I have the 50/0.55 and I'd say your second shot looks right with regards to resolution (with a 150mm tube lens). I think I see a tiny hint of lateral CA though and haven't seen that on my copy. But I've never shot such a starkly contrasting target with it. I assume these were centre of the frame crops. You'd expect an APO design to be perfect in this regard (certainly for longitudinal CA anyway - and this looks fine here), but any number of other things could be causing some slight lateral CA instead (spacing between tube lens and mitty, the tube lens itself etc).

Edit: just a thought - is your diffraction grating under a cover slip? That might induce a bit of colour fringing.

Munich
Posts: 28
Joined: Mon Jun 16, 2014 5:36 am

Post by Munich »

Thank you Beatsy, that helps. And, you are right:
the grating element is enclosed in a chunk of glass that weighs almost two pounds.

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