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Surprising fluorescence


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#1 Alex_Mustard

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Posted 06 October 2005 - 10:41 AM

Fluorescence is pretty common underwater. It is when a subject absorbs light of one colour and emits light of another. It is usually pretty hard to capture photographically.

I am sure you have all seen examples of fluorescence - such as an Anemone fluorescing red, or a mushroom coral fluorescing orange or green, or in the Caribbean a coral, often the great star coral (M. cavernosa) fluorescing orange. These are just examples I can think of now.

Generally the way it works is blue light (i.e. underwater ambient light - and usually reasonably deep) shines on the subject and it emits fluorescent light of a different colour. And it is only certain individuals that fluoresce - it never seems to be all the population. This is a completely different process to phosphorescence or bioluminesence.

There is a good explanation here: http://www.nightsea.com/aboutfluor.htm

Anyway it has always been difficult to capture. When you see your bright red anemone or bright orange coral you take a picture (with flash) and it comes out brown and much more muted than it looked underwater. In fact usually they look like all the other corals do.

Curiously I have found that available light images (taken with a filter - presumably of any brand) will capture this fluorescence as it appears underwater.

Here is an example of Great Star Coral in Cayman - that was clearly fluorescing underwater:

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and

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You can see from the first picture that I was able to capture the fluorescence while rendering the rest of the reef (and my fin in the bottom left corner!) in normal colours.

Alex

p.s. The next day I photographed some other fluorescent coral with flash for comparrison that I will post once I have found them.

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#2 Alex_Mustard

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Posted 06 October 2005 - 10:52 AM

OK, I dug out a flash lit version. This was different individual, but showed the same fluorescence. Once I shot with the flash this coral looks brown, just like all the others:

Posted Image

Again I included my fin in the corner of the shot (for comparrison purposes, honest) :D

Alex

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#3 Alex_Mustard

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Posted 06 October 2005 - 10:54 AM

And finally, after taking the last shot I then turned the flashes off. And took an available light image.

Posted Image

I can actually see hints of the fluorescence in this shot - but no where near as much as it looked at the time - (which is what you see in the filter shots at the start of this thread).

Alex

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#4 acroporas

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Posted 06 October 2005 - 11:23 AM

Wow, that is really cool.

I have a fealing that images like this will be accused of over photoshopping.
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#5 james

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Posted 06 October 2005 - 11:38 AM

Alex,

I've always been disappointed when photographing flourescent animals - because the results from the flash are pathetic! Thanks for the tips. I was particularly disapointed to get such a blase image of this rose E. quadricolor anemone in Bali on the Liberty Wreck (you probably saw it too):

Posted Image

Under normal sunlight or aquarium lamps these anemones really "pop."

Cheers
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PS, how did you get your fin in the TOP of the shot Alex, were you standing on your head???? Anything to get the shot dude. :-)
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#6 Chris Bangs

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Posted 06 October 2005 - 06:31 PM

I have had some luck capturing the fluorescence on Anemone tips but underexposing the flash output. Green, yellow, and Pink can be captured this way but the bright red as seen on Guam still is an issue. Digital does a better job than fime did on the red but still nothing like what it looks like in natural light.

I will try the magic filter next month on the red anemones when I am on Guam.

I have always wanted to try using a black light filter over the strobes but I have been unable to find something that can be used underwater

I included examples where some or most ( inthe case of the green and pink ) of the color was retained

Posted Image

Posted Image

Posted Image

Posted Image
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#7 MikeVeitch

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Posted 06 October 2005 - 08:28 PM

Aha, you took the idea straight off my tongue!

I was wondering the same thing the other day. I too have always been disappointed with how ugly bright red anemones come out on flash shots. However, in video with the red filter it looks the bright pink/red that the eye sees. Sooo...i have wanted to try the Magic on it myself, unfortunately there are only two of them that i know of in Yap and i haven't been diving on those sites in quite some time....Of course as soon as a dive guide surprises me and takes us there i will be set up with the video or the 105mm or something....
:D

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#8 anthp

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Posted 06 October 2005 - 09:02 PM

Aha, you took the idea straight off my tongue!

<{POST_SNAPBACK}>


Eeew... :D
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#9 Tom_Kline

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Posted 07 October 2005 - 09:27 PM

Cool shots! The filters you used for the pix in the first post must have functioned as a barrier filter such as used in fluorescence microscopy. With blue excitation the barrier filters are yellow. At depth, e.g., 30m, the ambient light is mostly cyan thus providing the excitation wavelength. The human eye to some degree adjusts for the ambient light much like with tungsten light so we see the fluorescence better than the camera. Try various filters to block the shorter wavelengths and viola' you've got the pix. Higher ISO would be useful too.
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#10 Snappy

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Posted 08 October 2005 - 12:49 AM

Alex, you mention black light and the diffifulty of finding a filter for underwater use. You may find a solution here (not only the 3100 dollar light...):
http://www.nightsea.com/exciter.htm
http://www.nightsea.com/convert.htm
http://www.nightsea.com/photoblue.htm
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#11 Alex_Mustard

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Posted 08 October 2005 - 01:51 AM

Thanks Guys,

I have used the Nightsea filters before. They work very well.
Posted Image

But you can only use them at night, and you have to swim round the reef zapping various subjects until you find a fluorescent one.

After my Nighsea filters were sent to the bottom of the ocean (for research reasons) I actually made up a set myself using sample filters from small Lee Filters product booklet. These worked pretty well too:
Posted Image

I agree with Tom about why it is working with the Magic Filter in daylight. The fluorescence is naturally excited by the blue ambient light, but unlike the ambient light shot the Magic Filter is then acting as a barrier to the excess ambient light, so that orange fluorescent light from the coral can be recorded. In the Flash lit shot the main light source is white light - so the reflected colours of the coral (i.e. normal brown) are recorded.

Alex

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#12 Chris Bangs

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Posted 08 October 2005 - 02:07 AM

Alex

did you try using a night sea filter during the day on a deep subject such as a red anemone?

I will take the magic filter down as soon as I can on Guam. there are some red bulb tip anemones at 60 feet that are almost neon like.

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#13 Alex_Mustard

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Posted 08 October 2005 - 02:12 AM

Its a while sinec I was playing with the Nightsea - but from memory it does need to be dark - or almost completely dark to get the shots. The Fluoresence is not very bright and therefore is easily overwhelmed by the ambient light.

Alex

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#14 JamesWood

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Posted 12 October 2005 - 01:50 PM

I've been playing with the Nightsea filters as well, so far only at night. . .

James
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