Questions about UV fluorescent photography

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physicsmajor
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Joined: Sun May 10, 2020 12:56 pm

Re: Questions about UV fluorescent photography

Post by physicsmajor »

Rogerly_Fluorescent.jpg
This is a macroscopic focus stack from a 14.8 cm wide specimen of fluorite from the Rogerly mine in England, lit from the left and slightly below with my Convoy with a Nichia U365 emitter, mixed with dim natural light from above. The Convoy was about 1.5 meters from the specimen. These new LW UV LEDs are awesome!

As a cautionary note, at least with my Nikons you generally need to dramatically underexpose to not blow out fluorescence (this varies by the color of fluorescence of course). No filtering was applied on the light source or camera side, and along the top/right you can see the natural deep green of this Rogerly fluorite. There is essentially no violet pollution; the brilliant blue is accurate for this particular specimen.

For comparison, here's the same specimen with same settings but natural light alone.
Rogerly_Natural.jpg

rjlittlefield
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Re: Questions about UV fluorescent photography

Post by rjlittlefield »

physicsmajor wrote:
Tue May 31, 2022 12:46 pm
No filtering was applied on the light source or camera side, and along the top/right you can see the natural deep green of this Rogerly fluorite. There is essentially no violet pollution; the brilliant blue is accurate for this particular specimen.
What settings do you use for nominal white balance?

--Rik

physicsmajor
Posts: 108
Joined: Sun May 10, 2020 12:56 pm

Re: Questions about UV fluorescent photography

Post by physicsmajor »

rjlittlefield wrote:
Tue May 31, 2022 12:48 pm
physicsmajor wrote:
Tue May 31, 2022 12:46 pm
No filtering was applied on the light source or camera side, and along the top/right you can see the natural deep green of this Rogerly fluorite. There is essentially no violet pollution; the brilliant blue is accurate for this particular specimen.
What settings do you use for nominal white balance?

--Rik
In this quasi-studio setup I match the in-camera white balance to the exact Kelvin color temp setting from a trusted bicolor LED panel, which lets me set its Kelvin color temp. I don't change that when adding the 365nm source. Keeping a little dim white light is deliberate, I find this is preferable for most UV work and 'proves' you haven't let the camera WB go off the rails. The fluoro colors captured then match reality in my experience.

For color rendition comparison, this site has a good example of a Rogerly fluorite under UV and white light https://www.naturesrainbows.com/post/20 ... erley-mine. The UV activity so strong that it gains a blue-teal tinge under sunlight, which is an effect known as daylight fluorescence.

jmc
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Re: Questions about UV fluorescent photography

Post by jmc »

Funnily enough, I just finished correcting the final proof of a paper I've written which covers some of what you are seeing here Mark.

With 'normal' colour cameras, there are filters which are supposed to remove the UV and IR before it reaches the sensor. However some cameras do this better than others. My Canon cameras for instance have quite 'leaky' filters especially around 365nm, and this typically produces red specular highlights in UV fluorescence images, while Nikon and Sony are more efficient at blocking this. It looks like you will need an additional filter to block the UV rather than just relying on the ones in the camera. Lou mentioned Zeiss T* filters. I'm glad to hear that as the Zeiss T* was the one I concluded that was the best option to replace the now no longer made Schott KV-418 (at least among the commonly available highstreet type filters).
Jonathan Crowther

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