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 Post subject: Photographing green tourmaline
PostPosted: Sun Mar 22, 2009 2:44 pm 
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Hi all,I'm sure someone must have experienced the same frustration I have when trying to make a pic of green/blue tourmaline look like it does in person.
My attempts usually result in the picture having brown or grey highlights which are actually not in the stone at all! Changing the lighting angles does not seem to help much. Maybe it's the type of light? I use a daylight spectrum fluorecent(nothing fancy at all) and it seems to work very well for just about all other colors.
This pic is a good example of what I'm talking about:
Image
This stone is a very pretty two tone blue and green but the picture does it no justice.

If anyone has some tips on resolving this issue I would be very happy to try them out!.

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PostPosted: Sun Mar 22, 2009 7:54 pm 
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what camera are you using?

look up bayes filtering on wikipedia...

then shoot it in incandescent light to deal w/ the filters.. u may need to photoshop..

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PostPosted: Sun Mar 22, 2009 8:47 pm 
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Quote:
Changing the lighting angles does not seem to help much. Maybe it's the type of light? I use a daylight spectrum fluorecent(nothing fancy at all) and it seems to work very well for just about all other colors.


That source has one big green line at 560nm or so, then gets "white" from blue and orange phosphors*... but is missing quite a few other wavelengths that are needed. Try a shot under open sky, not direct sunlight. Or as suggested, tungsten with filtration.

We have discussed metamerism in the past I think..

"The term illuminant metameric failure is sometimes used to describe situations where two material samples match when viewed under one light source but not another. Most types of fluorescent lights produce an irregular or peaky spectral emittance curve, so that two materials under fluorescent light might not match, even though they are a metameric match to an incandescent "white" light source with a nearly flat or smooth emittance curve. Material colors that match under one source will often appear different under the other."

* Just because a human eye perceives it as "white" does not mean that it is spectrally a continuum. The eye has automatic white balance so that after a while colors even in candlelight begin to look amost "Normal".

What you see is often not what you get when film or a CCCD wants to call "White" a mixture of narrow bands of blue/green/red or cyan/yellow/magenta, and your eye shrugs and says, "White is something that is not black".

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PostPosted: Sun Mar 22, 2009 9:16 pm 
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Thanks for the suggestions guys!
The Camera is a nikon d40,an excellent camera by all acounts,I can't say the same for the lens but that isn't the problem.
The photoshop /Bay's filtering idea sounds okay but I already do minimal photoshop editing like cropping and some sharpening and have the capability to change the photo but was looking more to reproduce as natural a pic with minimal editing as my camera is capable of doing with most stones.
I will definitely try some other light sources with more natural daylight spectrum and possibly natural sunlight and post the results.

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PostPosted: Sun Mar 22, 2009 11:55 pm 
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I've played around with a few different light sources. Over the last bit, I've actually found a mixture HPS (high pressure sodium) and MH (metal halide) arc lamp to be quite impressive... these are often used in indoor greenroom application (though the price-sensible approach would be using the ones they sell at hardware stores). They do have 'peaks' in their spectrum, but the areas around the peaks are not devoid of light, just weaker.


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PostPosted: Mon Mar 23, 2009 1:04 am 
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I've faced the same problems trying to take some photos of some deep green chrome tourmalines... they turn out reddish or green/brown depending on the stone.

I have a D40 with all the internal processing turned off (as much as Nikon lets you anyhow). I have tried tungsten, the GE Reveal tungstens, and two different types of compact flourescent bulbs with no appreciable difference. I also calibrate my exposure and white balance with an 18% grey card prior to shooting the stones.

I suspect it has to do with the filter over the sensor itself... acting something like a Chelsea filter.

For almost all other stones the colours come out pretty much spot-on. It's just those chrome tourmalines for me.

Oh, wait, I remember there was one stone that positively lit up on the camera but in person was a normal colour. Can't remember the details, but it was so unreal - think of a neon paraiba when the stone itself was a pale aquamarine.

I'm glad to hear it's not just me! I was beginning to think I was losing it.

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Last edited by gembug on Mon Mar 23, 2009 4:30 am, edited 1 time in total.

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PostPosted: Mon Mar 23, 2009 4:07 am 
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bayes filtering does a Green 1.0/Red .49 / Blue .51 or so.. to match human eyeball sensitivity. Toss it in photoshop, bust out the channels and multiply by the inverse co-efficients to get it back to reality. Then try your modifications. You may need to use "raw" format.. not sure w/ your camera.

Each camera has a specific manufacture degree of bayer filtering..that's the one (from memory) for my canon, but its close enough to the 2:1:1 ratio that it'll work.

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PostPosted: Mon Mar 23, 2009 5:55 am 
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Hi,
I'm using a 60W 'normal' tungsten daylight bulb (made by phillips, them blue ones ;) I buy 'm here for a few bucks at any hardware store) and have very little trouble capturing accurate colour. They throw a nice, even spectrum.

I've seen 'm in 60W and 100W. There is higher wattage 'photoflood' bulbs on the market but they have a very limited lifetime.

used this picture before in another example but it fits in here as well:

Image

accurate colour, taken with a 60W philips daylight tungsten bulb.


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PostPosted: Mon Mar 23, 2009 6:49 am 
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I've seen 'm in 60W and 100W. There is higher wattage 'photoflood' bulbs on the market but they have a very limited lifetime.

Now that you mention it, back in the fossil days of film, I used to get the 150 Watt tungsten photofloods made with blue glass. I used them for industrial product photography and they did work well. As you say, short-lived, and HOT.

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PostPosted: Mon Mar 23, 2009 8:18 am 
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I'm using a 60W 'normal' tungsten daylight bulb (made by phillips, them blue ones I buy 'm here for a few bucks at any hardware store) and have very little trouble capturing accurate colour. They throw a nice, even spectrum.
Sounds like an inexpensive idea and worth trying too,good color on that retangle.

Thanks again for the excellent advise to everyone that responded,very interesting stuff indeed.Since I have no sunlight today (raining) I will try to pick up one of the phillips bulbs and shoot some more pics,also photoshop and post results tonight.

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PostPosted: Mon Mar 23, 2009 8:28 am 
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I like them blue lightbulbs too. Here is a webpage about them. :) The picture in my avatar was taken using only such a lamp. I've had good results with all kinds of stone colours, from red over yellow to green. Oddly enough, not with deep blue though... That seemed to like a regular bulb more than a blue one.

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PostPosted: Thu Mar 26, 2009 12:55 pm 
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I prefer taking pictures on an overcast day or using a northern exposure if it's sunny. The biggest problem that I have is in getting the exposure right. If I reduce the light, my camera, (an older Nikon 4300), just tries to compensate and I still get an over exposed, fuzzy area in certain sections of the shot. I suppose that I should take the time to set up a consistent lighting setup, but I prefer to run around outside trying to find the "perfect" lighting situation and then standing on my head or hanging from a tree to get the stone at just the right angle. Here are some green tourmaline shots that have only been cropped and sharpened a bit.

ImageImageImage

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PostPosted: Thu Mar 26, 2009 6:59 pm 
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Michael
I like the way the color came out. No substitute for natural light!

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PostPosted: Sat Mar 28, 2009 12:40 am 
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Wow Michael - those are great photos for using a 4300! I have one of those and gave up trying to get close-ups like that.

A tip for getting the proper exposure and such is to buy yourself an 18% grey card. Lay it out on the surface you're taking the photo on, and then use the camera's custom white-balance measurement to set the colour. Then use the same card, same position and set the exposure lock. Replace the card with your gem and you should get pretty close to true colours and proper exposure.

It was the only way I could get even close to capturing the violet-blue tone and deep saturation of the fantastic Afghan Lapis I love.

I can't remember the exact steps but it worked for me (before I switched to a Nikon D70 which blew up and was just replaced with a D40).

Hope this helps,

-Allan

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