Ultra-violet photography with digital cameras?

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chrish
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Ultra-violet photography with digital cameras?

Post by chrish » February 1st, 2014, 10:03 am

Anyone here have trouble photographing fluourescent things (scorpions, etc) with you digital camera?

Reading this discussion (http://www.dyxum.com/dforum/ultraviolet ... 81951.html) it appears that many digital cameras have internal cut filters that are needed to block out infrared radiation and that these filters also block out ultraviolet light. Therefore it takes long exposures to get any decent UV image on the sensor.

I have tried this several times and here's what I get. These photos are shot with the Sony A-700 DSLR (CMOS):

Flash photo (for comparison)

Image

UV straight out of the camera using the same settings as the above photo (auto white balance on) (ISO 640, 1/30th at f/2.8) -

Image

UV with some post process (white balanced as much as I can and desaturation of purple)

Image

It isn't bad that way, but I wonder if anyone else has had better luck?

I know the brand/type of UV light might be influencing this, but I'm wondering if anyone has found a good methodology either in camera settings or post process.

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Re: Ultra-violet photography with digital cameras?

Post by Owen » February 1st, 2014, 10:11 am

Any information about your UV source? Spot or flood? Wavelength? I actually think a camera with an EVF allows you to see the exposure better than trusting the AE to do it for you.

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 1st, 2014, 10:26 am

Owen wrote:Any information about your UV source? Spot or flood? Wavelength?
I believe I was using my older Inova X5 which has 5 LEDs and a flood pattern.
It is supposedly around 365/390mm UV light mix according to a review I read online.

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Re: Ultra-violet photography with digital cameras?

Post by Owen » February 1st, 2014, 10:43 am

I'm wondering if manually setting the WB to daylight (~5000) would help.

My scorpion shot on the other thread was ISO-800, 1/125, f6.3 at about 1:2 life size; the millipede was ISO-400, 1/60, f7.1 at closer to 1:3 life size. It may be that a stronger 'spot' source works better since light can be directed at the subject. I was also spotting the scorpion from about 8" and the millipede from about 12" while holding the light just under the lens.

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Re: Ultra-violet photography with digital cameras?

Post by sjfriend » February 1st, 2014, 10:34 pm

I have noticed different looks using different lights. With film had to use long exposures to get proper look. Do notice that using digital the uv light shows up more on the ground.

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 2nd, 2014, 8:58 am

Owen wrote:I'm wondering if manually setting the WB to daylight (~5000) would help.
Unfortunately, the color temperature of UV light is somewhere in excess of 12,000 Kelvin so most (all?) cameras can't be set to color temperatures in this range.

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Re: Ultra-violet photography with digital cameras?

Post by Owen » February 2nd, 2014, 9:48 am

chrish wrote:
Owen wrote:I'm wondering if manually setting the WB to daylight (~5000) would help.
Unfortunately, the color temperature of UV light is somewhere in excess of 12,000 Kelvin so most (all?) cameras can't be set to color temperatures in this range.
But you're trying to photograph the fluorescing, not the actual UV balance. My camera records it at about 3600K when set to AWB, but I rebalance it in Lightroom to about 4500K since that appears closer to what my eye is seeing.

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 2nd, 2014, 4:52 pm

Owen wrote:But you're trying to photograph the fluorescing, not the actual UV balance. My camera records it at about 3600K when set to AWB, but I rebalance it in Lightroom to about 4500K since that appears closer to what my eye is seeing.
Good point. I wasn't thinking about the lower energy level of the fluouresecence.

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Re: Ultra-violet photography with digital cameras?

Post by umop apisdn » February 5th, 2014, 10:23 am

Several years ago, I was powder tracking gopher tortoises to check out their feeding/surface activity patterns. I used a UV flashlight to illuminate the fluorescent powder. I was using a Canon EOS Rebel XTi at the time, and I recall the photos actually coming out pretty nicely, considering I was photographing them handheld at night.

I'll have to do some digging to see if I can find those photos.

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 5th, 2014, 10:26 am

umop apisdn wrote:Several years ago, I was powder tracking gopher tortoises to check out their feeding/surface activity patterns. I used a UV flashlight to illuminate the fluorescent powder. I was using a Canon EOS Rebel XTi at the time, and I recall the photos actually coming out pretty nicely, considering I was photographing them handheld at night.

I'll have to do some digging to see if I can find those photos.
I did some similar stuff with Cophosaurus and Ammospermophilus many years ago (pre-digital). Never thought about trying to photograph the trails. The Cophosaurus were funny since they apparently sleep out in the open. Walking up to a fluorescent green or orange lizard sleeping in the middle of a desert flat or dirt road in the dark is kind of mind-blowing.

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Re: Ultra-violet photography with digital cameras?

Post by umop apisdn » February 6th, 2014, 5:53 pm

Well, I don't recall the photos being all that great for visualizing the tracks themselves. Not before long, most tracks would reduce to following small patches of grass where lingering powder brushed off the plastron, and at times I was on hands and knees with my face inches from the sand, trying to detect even a single speck of powder. It was a bit unnerving the time I realized I was following snake tracks in that manner. Never found the snake, though...just noticed the serpentine trail heading in a single direction.

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Re: Ultra-violet photography with digital cameras?

Post by Alex H » February 9th, 2014, 8:07 am

Thank you Chris, for reading my article on Dyxum.com (the link in the original post).

What you have recorded with your camera is a combination of UV-induced visible fluorescence of the scorpion, and the reflectance of violet light (emitted by the torch) from the soil and rocks. There is no actual UV recorded in this picture, because as you correctly pointed out cameras internal cut filter (hot mirror) will block most of it from reaching the sensor. Especially at such shorts exposures. I have gotten very similar results when photographing scorpions in Arizona. Look at this picture:

Image

This happens because many LEDs rated at 390nm will also produce sufficient amount of violet light in a range of at least 400-405nm for it to be recorded by the camera. If you want to record UV-induced visible fluorescence, you will have to get a UV torch that does not produce any visible light. I use rather expensive Nichia 365nm LEDs and in addition I mount UV-pass filters on top of LEDs to minimize even more that almost negligible amount of visible violet light that these LEDs produce. I wrote a short post about it on my web site.

You can also use your current torch, but but a yellow filter on the camera lens. It should filter out UV and ultraviolet, and should give you a better image. Unfortunately, if there is any fluorescence in violet or blue, the filter will block it. One more thing to remember is that some older yellow filters may fluoresce themselves, so should not be used for such application.

If you want to record reflected UV light, than I would recommend to use full-spectrum modified camera with internal cut filter removed from it.

I hope what I wrote will be useful.
Alex

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Re: Ultra-violet photography with digital cameras?

Post by Owen » February 9th, 2014, 3:26 pm

Cool stuff Alex. I'm playing with a Nitecore CU6 which has a 365nm, 3W LED. It does seem to just affect the fluorescing subject:

Image

Image

Image

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 12th, 2014, 5:09 am

Interesting. So the key seems to be finding a UV light with significantly narrower or at least lower wavelengths (i.e. 365 vs 395) to avoid the purple fluorescence. The camera should filter out the UV and in a perfect world you would only see the fluorescence of the scorpion.

The problem I see with using a yellow filter is that it would alter the perceived color of the scorpion's fluorescence.

Looking into this more.

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Re: Ultra-violet photography with digital cameras?

Post by Alex H » February 13th, 2014, 11:09 am

Owen wrote:Cool stuff Alex. I'm playing with a Nitecore CU6 which has a 365nm, 3W LED. It does seem to just affect the fluorescing subject:
It does indeed look like the Nitecore torch does not produce any noticeable visible, which is very good. Yoru pictures are much clearer and have nicer colors.
I do not know what type of LEDs the Nitecore torch uses though. It would be interesting to find this type of information.

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Re: Ultra-violet photography with digital cameras?

Post by Alex H » February 13th, 2014, 11:17 am

chrish wrote:Interesting. So the key seems to be finding a UV light with significantly narrower or at least lower wavelengths (i.e. 365 vs 395)...
That is why it is good to know the emission spectrum of LEDs when purchasing. Unfortunately, many lower cost LEDs do not even mention what type of chips they have.
chrish wrote: ... to avoid the purple fluorescence...
Please note that the "purple" color of the background soil is not fluorescence.
chrish wrote:The problem I see with using a yellow filter is that it would alter the perceived color of the scorpion's fluorescence.
I totally agree about that. That is why I use higher quality LEDs centered arounf 365nm, and, in addition, have Schott UG11 glass installed in front of the LEDs, to completely block that minuscule amount of violet that these LEDs produce.

If You follow the link to my web page (http://www.holovachov.com/fluorescence), at the bottom, there are a number of useful links and references, related to UV induced visible fluorescence photography.

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Re: Ultra-violet photography with digital cameras?

Post by Owen » February 13th, 2014, 3:59 pm

Alex H wrote:I do not know what type of LEDs the Nitecore torch uses though. It would be interesting to find this type of information.
I can't find any info on the UV chip from their literature. The white XP-G2 is a 3.45mm square chip, but the UV chip is bigger and looks like it's 5mm. I actually got it when it was on sale at 20% off (~$88) which seemed reasonable for a multi-purpose unit. When the weather gets warmer, I'll see how well it works on a sheet for black lighting for insects.

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 13th, 2014, 6:20 pm

Alex H wrote:.
chrish wrote: ... to avoid the purple fluorescence...
Please note that the "purple" color of the background soil is not fluorescence.
Of course. I just like trying to spell fluorescence so I type it every chance I get, even if it doesn't apply. ;)
Alex H. wrote:I totally agree about that. That is why I use higher quality LEDs centered around 365nm.
There are a few affordable 365 nm lights on Amazon. The only question might be whether they are truly 365 or not. One of the reviews I read said a person tested one unit and found it closer to 370 nanometers. That's still probably close enough to achieve our goal here. I may have to try one of these cheap lights just to see what $15 can buy.

BTW - awesome discussion on that link :beer:

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 14th, 2014, 10:53 am

Just for kicks, I took my cheap version of my UV scorpion light (I bought it online from China for about $6) and ran it through a spectroscopy program.

Here's the output. I didn't calibrate the machine first so the numbers might not be perfect, but.....

Image

Notice the peak wavelength is somewhere around 425nm which is well within the visible range. There is as much if not more light in the 450 range as there is in the lower UV 350 range.

Also notice that this light does emit some UVB and UVC which are the harmfull wavelengths of UV radiation. Might be a good idea to get the eye protection and not just point these at your skin for long periods.

I ordered a supposedly narrow range 365nm light and will see how this compares.

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Re: Ultra-violet photography with digital cameras?

Post by Alex H » February 15th, 2014, 1:28 am

What kind of software is that?

Torches with Nichia LEDs that I use are on average 200 USD in Europe.

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 15th, 2014, 7:39 am

Alex H wrote:What kind of software is that?.
I don't recall the name. I asked one of our physics faculty if he could measure the wavelengths of my UV light and he let me use a little USB spectrometer and a software program that read from it. I will look next week for the name.

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Re: Ultra-violet photography with digital cameras?

Post by Owen » February 18th, 2014, 6:26 pm

One more from today. I did the exposure so that the background was decently lit and balanced and that only the scorpion (Uroctonus mordax) is affected by the UV:

Image

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Re: Ultra-violet photography with digital cameras?

Post by Alex H » February 19th, 2014, 10:12 am

The last image is very nice, but the scorpion now looks like it is made from plastic :)

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Re: Ultra-violet photography with digital cameras?

Post by Owen » February 19th, 2014, 4:50 pm

Alex H wrote:The last image is very nice, but the scorpion now looks like it is made from plastic :)
I think that part of that is due to the sky reflections. UV was coming from the side and some ambient light from the top.

Here's Harpaphe haydeniana from the same day. You can see the true black and yellow color on the one in the background that is partially shielded from the UV:

Image

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Re: Ultra-violet photography with digital cameras?

Post by umop apisdn » March 13th, 2014, 7:03 pm

I finally got around to the images I took while I powder tracked gopher tortoises, of course they were better in my memory. Nevertheless, here's a shot. Not terrible, considering I was using a 3.2 MP Nikon Coolpix in the darkness without a flash, my only illumination being the UV light I used to detect the powder.

Image

Considering it's about a 7 year old photo and the fact that it was taken with a point and shoot in regular JPEG mode, I don't know that there's too much improvement to be had from the image.

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Re: Ultra-violet photography with digital cameras?

Post by chris_mcmartin » February 3rd, 2015, 7:07 am

In a magazine from a different hobby of mine, an article says the following:
Create glowing photography by using fluorescent-lighting setups on your subjects . . . The key is to fit strong blue filters for the strobes and a yellow filter on the lens. The resulting photos will show fluorescent colors produced within the subject rather than the reflected light we normally see.
This seems like a crude aproximation of UV photography...anyone here have the means to try it, with a captive scorpion perhaps?

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Re: Ultra-violet photography with digital cameras?

Post by chrish » February 3rd, 2015, 8:05 am

chris_mcmartin wrote:This seems like a crude aproximation of UV photography...anyone here have the means to try it, with a captive scorpion perhaps?
The problem with this approach would be it would give the "appearance" of UV fluorescence (e.g. the bright colors etc) but in fact wouldn't be utilizing light from the UV wavelength therefore the scorpion wouldn't actually be fluorescing.

My assumption is that the lights you would be using don't release strong UV wavelengths and that even if they did (they would have to have warnings if they did!) the blue filter would probably remove some subset of the wavelengths below 450nm.

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Re: Ultra-violet photography with digital cameras?

Post by chris_mcmartin » February 3rd, 2015, 8:21 am

chrish wrote:
chris_mcmartin wrote:This seems like a crude aproximation of UV photography...anyone here have the means to try it, with a captive scorpion perhaps?
The problem with this approach would be it would give the "appearance" of UV fluorescence (e.g. the bright colors etc) but in fact wouldn't be utilizing light from the UV wavelength therefore the scorpion wouldn't actually be fluorescing.
Yes, that's why I think it's a "crude approximation." The photo they showed as an example was pretty cool (sea anemones); I just wonder what a scorpion (known to fluoresce) would look like under a similar setup.

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