• Ultraviolet Photography
  •  

This experiment didn't work out.

3 replies to this topic

#1 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,094 posts
  • Location: USA

Posted 05 October 2017 - 16:56

I set up a crumpled aluminum foil experiment yesterday to illustrate chromatic aberration in UV-capable lenses. It did not work out well because the little yellow "target" flower in the center of the foil and the surrounding grass created masses of colourful reflections on the foil which naturally confused the search for purple or cyan/magenta fringing.

Oh well. I can always try again. I'm thinking that I'll put the crumpled foil in a small light box with white walls and background. That should lesses stray colour reflections.

Here are a few shots to show you what I was trying to do. :D :rolleyes:

D610 + Coastal Optics 60/4.0

This lens is a UV/Vis/IR colour corrected lens. We would expect little chromatic aberration. However, there are so many colours floating around on the foil, that it might be difficult to decide what should not be there. There is also a grating effect from the foil surface Still, I think I see no obvious signs of fringing.

Visible [f/5.6 for 1/3200" @ ISO-400 with Baader UV/IR-Cut Filter in Sun]
Attached Image: coastal60-4_visSun_20171004wf_6961pn01.jpg

Visible [unresized excerpt from full-sized version of preceding photo]
Note grating effect from foil surface causing a kind of "iridescence".
Attached Image: coastal60-4_visSun_20171004wf_6961pn0101.jpg

Visible [unresized excerpt from full-sized version of preceding photo]
What is this blue from? Is foil slightly blue so that is shadows become darker blue?? Or maybe there are blue sky reflections.
Attached Image: coastal60-4_visSun_20171004wf_6961pn0102.jpg

Ultraviolet [f/5.6 for 1/6" @ ISO-400 with Kolari UV-Pass Filter in Sun]
I could not really get a firm white balance in the UV shot(1*). There are tinges of false cyan and false purple as well as the expected false yellow and false blue.
Attached Image: coastal60-4_uvKolariSun_20171004wf_6966pn01.jpg

Ultraviolet [unresized excerpt from full-sized version of preceding photo]
Attached Image: coastal60-4_uvKolariSun_20171004wf_6966pn0102.jpg

Ultraviolet [unresized excerpt full-sized version of preceding photo]
Attached Image: coastal60-4_uvKolariSun_20171004wf_6966pn0101.jpg

(1*) ADDED LATER:
The fix for that missed white balance is to shoot a white card with the given camera + lens + filter + illumination for use in your converter. Here I was relying on an existing D610 colour profile together and random stabs on neutral areas with Photo Ninja's white dropper. That works 98 times out of 100. Here it was less successful.


D610 + Micro-Nikkor 105/2.8D

This lens, an older version of the current Micro-Nikkor 105/2.8G AFS, is somewhat UV-capable. Again there are so many colours present in the foil that it could be difficult to say what colours are fringing and what are simply from reflection.

Visible [f/5.6 for 1/3200" @ ISO-400 with Baader UV/IR-Cut Filter in Sun]
There seems to be some purple/magenta fringing to the right of the flower.
Attached Image: nikonUVnikkor105-4.5_visSun_20171004wf_6882pn01.jpg

Visible [unresized excerpt from full-sized version of preceding photo]
Attached Image: nikonMicroNikkor105-4.8D_visSun_20171004wf_6920pn03.jpg

Visible [unresized excerpt from full-sized version of preceding photo]
Attached Image: nikonMicroNikkor105-4.8D_visSun_20171004wf_6920pn04.jpg

Ultraviolet [f/5.6 for 1/6" @ ISO-400 with Kolari UV-Pass Filter in Sun]
Because this lens would not be corrected in the UV, we should expect to see some fringing and perhaps we do here. But because the typical white balanced UV shot is expected to show false yellow and false blue, can we be sure? I need to try a more controlled experiment before saying 'yes'.
Also note that this lens did not produce quite the bi-coloured false yellow/blue flower that the CO60 did above. That suggests to me that its UV transmission range is not very wide.
Attached Image: nikonMicroNikkor105-4.8D_uvBaaderSun_20171004wf_6923pn01.jpg

Ultraviolet [unresized excerpt from full-sized version of preceding photo]
I'm pretty sure there is obvious purple fringing here. But a better experimental set-up might remove the remaining bits of doubt. "-)
Attached Image: nikonMicroNikkor105-4.8D_uvBaaderSun_20171004wf_6923pn0102.jpg

Ultraviolet [unresized excerpt full-sized version of preceding photo]
Attached Image: nikonMicroNikkor105-4.8D_uvBaaderSun_20171004wf_6923pn0101.jpg
Andrea G. Blum
Often found hanging out with flowers & bees.

#2 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,094 posts
  • Location: USA

Posted 05 October 2017 - 20:40

Edit: added small comment about white balance.
Andrea G. Blum
Often found hanging out with flowers & bees.

#3 OlDoinyo

    Member

  • Members(+)
  • 454 posts
  • Location: North Carolina

Posted 05 October 2017 - 22:54

Try roughing up the foil rather than crumpling it--either by manual means such as steel wool, or by etching briefly by spraying with drain cleaner or lye solutions and rinsing off with plain water.

#4 Andrea B.

    Desert Dancer

  • Owner-Administrator
  • 5,094 posts
  • Location: USA

Posted 06 October 2017 - 02:11

Will do !! Thanks for the suggestion.
Andrea G. Blum
Often found hanging out with flowers & bees.