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silica deposits
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dickb



Joined: 05 Jul 2010
Posts: 209

PostPosted: Mon Sep 30, 2019 5:39 am    Post subject: Reply with quote

Hallo Wim,

You're welcome to test any lens in my collection, I have a couple of (Apo) Xenoplans and MeVis-C lenses that may work for you. Alternatively, if you want higher resolution and have a monochromatic workflow, Lou has used lenses like XR Heligons with monochromatic light sources with interesting results. I have a few of those lenses you could try as well. I don't have any of those lightsources though

Dick
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Lou Jost



Joined: 04 Sep 2015
Posts: 3836
Location: Ecuador

PostPosted: Mon Sep 30, 2019 6:18 am    Post subject: Reply with quote

Dick makes a good point--since you don't care about color, for any lens you could increase resolution and eliminate chromatic aberration completely by using readily-available violet laser light, diffused through a milk diffuser to eliminate the speckle pattern. And there are lenses designed for specific wavelengths or wavelength ranges. But just changing to short-wavelength lasers would greatly improve any set-up regardless of lens. The violet lasers are very cheap.
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iconoclastica



Joined: 25 Jun 2016
Posts: 228
Location: Wageningen, Gelderland

PostPosted: Mon Sep 30, 2019 12:44 pm    Post subject: Reply with quote

Hmm, Dick and Lou, this surprises me. I thought along these lines a couple of years ago and I even did a test with a dark-blue filter (passing higher frequencies). The result was worse than without filter. I reasoned that I only excited the blue sub-sensels thus using only 1/4th of the sensels, and left it at that.

For the project shown above I got all the resolution I need, except in the z (depth / forward) dimension. But I can think of other possibilities.

For non-moving objects, monochome should never be a handicap: just run the stacl once again in white light and combine the luminosity of the monochrome stack with the colour of the full spectrum stack.
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Lou Jost



Joined: 04 Sep 2015
Posts: 3836
Location: Ecuador

PostPosted: Mon Sep 30, 2019 12:51 pm    Post subject: Reply with quote

Ah, yes, if you are going to do monochrome, it is best to have a monochrome sensor with no Bayer filter. These are readily available in smaller sensor sizes as astrophotography cameras; they also usually have cooled sensors, which reduces the noise tremendously. Alternatively a pixel-shifting normal camera will also sample each color at each pixel location, but without the cooled sensor. Full-frame monochrome cameras remain expensive, so for full frame the pixel-shifting (even just four-shot shifting like the Pentax k-1) is the best route. I use both solutions; a cooled monochrome MFT camera and pixel-shifting FF cameras. But I have not done much with the FF cameras in monochrome yet.....
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