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Myosotis sp. [Forget-Me-Not]: Stacking a Tiny Flower

Conical Cells
28 replies to this topic

#21 Andy Perrin

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Posted 15 July 2020 - 20:47

No, it’s not fluorescence because that would be in visible light. This is in the UV photos around highlights and specular reflections.

#22 Stefano

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Posted 15 July 2020 - 21:04

Visible light from fluorescence can reach the sensor if the filter is not rear mounted (if you screw it in front of the lens). The only other thing I can think about the lens are coatings. You said that it doesn't happen with all lenses, so the origin of the problem should be in the lens. Bright objects can maybe produce reflections inside the lens, as the coatings are not optimized for UV.

Does the problem disappear or is mitigated if you mount the filter in the back of the lens?

#23 Andy Perrin

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Posted 15 July 2020 - 21:07

No, rear mount is identical. It's not a coating issue either because I have two otherwise-identical El-Nikkor 80mm/5.6 metals, one of which has the problem and the other of which does not. See this ancient thread:
https://www.ultravio...r-80mm56-tests/

Edited by Andy Perrin, 15 July 2020 - 21:16.


#24 Andrea B.

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Posted 15 July 2020 - 21:31

Some of that "glow" or "fog" could be from stacking? A specular reflection does not necessarily bounce in the same direction each time. (Not sure if I said that correctly?) One would have to ensure the lighting was precisely in the same place for each shot in the stack. And you could still get differently directed specular reflections because the flower might "breathe" also on the cellular level. I've had some flowers which just flat out move when the UV flash hits them.

Or specular reflections could induce a bit of flare? Or the camera in use may not handle specular reflections/highlights well resulting in some pixel "bloom" -- like, spillover into another pixel?

So there's 3 guesses. Anything sound reasonable? :grin:

Thought of a 4th possibility.
UV photos take longer to expose. So the time spent making a UV stack is quite a bit longer than it takes to make a Visible stack. The slight wilting or organic movement of a flower during the UV stack making could contribute to a kind of stacked motion blur (not sure what to call it) because the stacking softwre cannot completely resolve the match up of the tiny details.

Still a spec-tacular result though!
Andrea G. Blum
Often found hanging out with flowers & bees.

#25 Andy Perrin

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Posted 15 July 2020 - 21:55

Yeah, so I was assuming that the glow in this case was the same as the problem I had in my old El-Nikkor but you may be right that it’s from something else stacking-related. I suppose the question could by answered by looking at an individual frame or two of the stack.

I don’t think it’s caused by movement. It looks pretty much like my old problem with the flare. But I don’t get why some lenses do it and not others.

#26 dabateman

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Posted 15 July 2020 - 22:11

I don't know the lens formula. But if there are cemented doublets and they start to separate, then you can get an odd double image or glow. That can be why you see it in one sample.


#27 UlfW

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Posted 16 July 2020 - 05:33

I am rather certain the "glow" is mostly a stacking artefact from out of focus image parts.
If I had used a tighter longer stack and much more retouching in Zerene that might have been improved a bit.
As it also lacks AR-coating ther is likely some flare caused by the different lens surfaces.

In the stack it did not look like local parts of the flower moved much, "breathing".
The total time for taking the stack was less than 90s.

The Milar is a simple triplet without any cemented groups.
It is a very old design.
Ulf Wilhelmson
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#28 UlfW

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Posted 16 July 2020 - 05:54

The visual image is taken with a few decades younger lens. I got the Milar last week.
Ulf Wilhelmson
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#29 Andrea B.

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Posted 16 July 2020 - 15:15

Thanks for the additional input on the stacking details. I really hope to see more such work from you. I have not yet been able to acquire the patience required for shooting a stack and working with Zerene Stacker. I really would like to try it though.
Andrea G. Blum
Often found hanging out with flowers & bees.