Pushing the 7.5x Mitu down to 1.8x on MFT

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mjkzz
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Post by mjkzz »

Lou Jost wrote:Sorry, I meant to write that the step size should be smaller!!!
Got it

I think all these amazing images you guys shot somehow might be masking some "truth" as people are "distracted" by aesthetics of image. I am trying to find some glass with grid on it and maybe just shoot those to see distortion, sharpness around, CA, etc.

Beatsy
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Post by Beatsy »

mjkzz wrote:
Lou Jost wrote:Sorry, I meant to write that the step size should be smaller!!!
Got it

I think all these amazing images you guys shot somehow might be masking some "truth" as people are "distracted" by aesthetics of image. I am trying to find some glass with grid on it and maybe just shoot those to see distortion, sharpness around, CA, etc.
You can get plastic diffraction gratings quite cheaply. The lines aren't very contrasty, but with a bit of pushing in post, they could work backlit.

This one is 1000 lines/mm, but I think I saw 2 micron once. https://www.ebay.co.uk/itm/Network-diff ... SwnH1WaFmh

Or a stage micrometer for epi objectives, but that would be more costly

Lou Jost
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Post by Lou Jost »

It is a very good practice to use more standardized, cleaner targets for such tests. Like Robert O'Toole does. Those tests are methodical and easily compared to each other, and I admire them. A set of different diffraction gratings, or a USAF target, are also really valuable and I should get one.

I think that using complex, real targets also provides valid relative information (for example, x is better than y). And I particularly like to use messy three-dimensional targets to tell me how colors look, and to see how images will behave when stacked; longitudinal chromatic aberrations in particular, if mild enough, can disappear when images are stacked, but for me the best way to test this is to make an actual stack of a subject I might like to use for real, and see if the LoCA really disappears. Likewise the quality of the out of focus areas is interesting sometimes.

Also, sometimes we want to know what is a good enough solution for our purposes, and the only way to know that is to shoot things we are interested in, and see how they work in our applications.

And frankly, I like to have an excuse to shoot beautiful butterfly scale patterns! I've joined the Sunset Moth club and the Morpho Club....

mjkzz
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Post by mjkzz »

Beatsy wrote:
mjkzz wrote:
Lou Jost wrote:Sorry, I meant to write that the step size should be smaller!!!
Got it

I think all these amazing images you guys shot somehow might be masking some "truth" as people are "distracted" by aesthetics of image. I am trying to find some glass with grid on it and maybe just shoot those to see distortion, sharpness around, CA, etc.
You can get plastic diffraction gratings quite cheaply. The lines aren't very contrasty, but with a bit of pushing in post, they could work backlit.

This one is 1000 lines/mm, but I think I saw 2 micron once. https://www.ebay.co.uk/itm/Network-diff ... SwnH1WaFmh

Or a stage micrometer for epi objectives, but that would be more costly
Can not order from eBay, will have too look for them in China

mjkzz
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Post by mjkzz »

And frankly, I like to have an excuse to shoot beautiful butterfly scale patterns! I've joined the Sunset Moth club and the Morpho Club....
no wonder the scales are so large, even at 1.8x, they are quite large. OK, anyways, ordered some stuff, they will come in next week

Lou Jost
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Post by Lou Jost »

Butterfly scales have nice ridges a few microns apart, just like diffraction gratings but prettier!

mjkzz
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Post by mjkzz »

Lou Jost wrote:Butterfly scales have nice ridges a few microns apart, just like diffraction gratings but prettier!
oh ok, is that why you chose butterfly scales? For some reason, I do not see any grating effect on your scale image, maybe I am missing something.

With the moth scale image I shot, I see that, actually, the wing exhibits different colors when looked at, suggesting different width of ridges, hence different diffraction.

Or I am not understanding it correctly?

mjkzz
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Post by mjkzz »

in fact, I think I am mis-understanding something, the "colorful" wings I shot probably is due to its iridescence, instead of grating.

Lou Jost
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Post by Lou Jost »

Sorry, I was not very precise. The ridges I am talking about are spaced several microns apart, and don't cause any special colors. They are just nice reference lines to check resolution of a lens.

You also made a good point above about the size of the scales. These scales are indeed bigger than usual. Normally I control for species differences by using my "universal target", the worldwide butterfly Vanessa sp. (cardui or its close relatives), so anyone anywhere in the world can easily get the same target and test their equipment. But this time the Morpho underwing patterns were so pretty that I could not resist.

I should add that the colors you see on iridescent lepidoptera are due to constructive interference of certain wavelengths caused by regularly-spaced plates or layers on the scales.
Last edited by Lou Jost on Tue Apr 24, 2018 5:34 am, edited 1 time in total.

mjkzz
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Post by mjkzz »

ah, thanks, I thought I read somewhere, probably here this forum, just do not remember which post, that lepidopterans are "colorful" due to iridescence, not pigmentation.

I measured the distance between (large) ridges in the center image, typically it is about 8 to 9 pixels, with GH5 sensor, that means they are 8.5 (average) * 3.28 (pixel size) / 5.556x = 5.02um, not sure if that can cause grating effect.

For grating test, CD or DVD might be good to start and let me see if I can even find one of them :D

ray_parkhurst
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Post by ray_parkhurst »

I find more problems with lenses in specular areas than in resolution or sharpness tests, which is why I continue to use coins as subject. Well...not the only reason...

rjlittlefield
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Post by rjlittlefield »

mjkzz wrote:ah, thanks, I thought I read somewhere, probably here this forum, just do not remember which post, that lepidopterans are "colorful" due to iridescence, not pigmentation.
Most of the colors are from pigmentation. The metallic sheens and iridescent colors, especially blues, are structural. See http://www.photomacrography.net/forum/v ... .php?t=704 for some further discussion and illustration.

--Rik

mjkzz
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Post by mjkzz »

rjlittlefield wrote:
mjkzz wrote:ah, thanks, I thought I read somewhere, probably here this forum, just do not remember which post, that lepidopterans are "colorful" due to iridescence, not pigmentation.
Most of the colors are from pigmentation. The metallic sheens and iridescent colors, especially blues, are structural. See http://www.photomacrography.net/forum/v ... .php?t=704 for some further discussion and illustration.

--Rik
ooops, thanks for correction, my mistake. I meant "due to iridescence,
and pigmentation, but not diffraction grating". Yeah, that is the post I read, before even joining this forum.

Lou Jost
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Post by Lou Jost »

mjkzz, the more I think about it, the more I agree with you. I really should be using more standardized and homogeneous targets like the wafers Robert uses. This would make my results easier to evaluate and compare. I'll definitely get some when I go to the US.

mjkzz
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Post by mjkzz »

thanks Lou. I think when testing, we need to take away one factor -- stacking skills, you guys are so skilled, the aesthetics of your works can be "distracting" :D

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