actinic photo question

[Rascal]

I am shooting with a Canon Powershot A710IS. My tank is lit with 10K MH supplemented with both T5 and VHO actinic. When all lights are on, I have finally started getting good color rendition by using the custom white balance setting. I stick something white in the tank (clean pvc fitting works good for me), then select white balance -> custom -> point & shoot -- and I'm all set.

 

My problem is that this doesn't work when I am trying to take actinic-only shots. None of the pre-set white balance options work well either. When I do the custom white balance, I can get most of the greens to come out, and some of the reds, but all of the blues and purples are completely washed out. It's better than auto, for sure, but still not what I want. The rocks for example, appear grey, when to the eye they have a distinct purplish cast (the coraline under actinics). I think the problem is that I don't really want my whites to look white when I'm shooting under actinics. I want them to look as they do to they eye. Just can't seem to figure out how to do this.

 

Any tips?

[dhoch]

Have you tried setting the white balance before turning of the 10K MH?

 

Dave

[Rascal]

Have you tried setting the white balance before turning of the 10K MH?

 

Dave

 

No. I hadn't thought of that. Will give it a try tonight and let you know how it works.

 

Thanks.

[Gadgets]

Do you have a sample photo that I can check out?

[Rascal]

Caveat: I know there are a lot of things wrong with these photos other than white balance. I'm just beginning to figure this stuff out -- long way to go.

 

I took a series of shots last night, trying to get the same images with only the white balance being different. So, . . . most of my actinic shots didn't come out at all since I failed to adjust the exposure values. Duh. My guess is I should slow the shutter speed way down rather than increasing the aperture, in order to keep the same depth of field. I will try again tonight. I may use my son's high chair as a make-shift tri-pod.

 

Here's what I have for now.

 

For reference, here is a FTS with custom WB - using the white PVC fitting put inside the tank for that purpose:

Tv: 1/125

Av: 5

ISO 200

(I know, too dark)

 

Here it is using the camera's "underwater" setting:

Tv: 1/80

Av: 4

Exp. Compensation: -2/3

ISO 200

 

Aside: these are taken with the outer 2 MH's on, center MH off, b/c I thought it would be too bright. Now I'm not so sure.

 

Unfortunately, I don't have the shot the Dhoch suggested (using the white balance setting with the MHs on), for the reason stated above.

 

Here's an actinic shot with custom WB set after the MHs went off:

 

Tv: 5

Av: 3.5

ISO 400

Wierd, huh?

 

And here's one with the "underwater" setting again:

 

Tv: 5

Av: 2.8

ISO 200

 

 

This series may be more helpful:

 

Tv 1/160

Av: 4

Exp. Comp.: -1

ISO 200

Custom WB using white PVC

 

Tv: 1/125

Av: 4

Exp. Comp.: -1

ISO 200

WB: underwater setting

 

Tv: 1/25

Av: 3.5

Exp. Comp.: -1

WB: custom using white PVC set while MH's were still on

 

 

Tv: 1/50

Av: 3.5

WB: underwater setting

 

To me it seems like the "true colors" of my tank are somewhere in between the custom white balance and the underwater setting. This is true with both actinic and full light shots. Hmmm.

 

Any advice is greatly appreciated.

Edited April 26, 2007 by Rascal

[fab]

If you are trying to take pictures with your actinic lights only, then you don't want white balance, as such. White balance is an adjustment to the color value of the image to 'bring it back" to what it should look like under true white illumination. So what you are doing is you are providing illumination that is far away from white then you are trying to get the camera to "bring it back" to white. The camera expects the spectrum of illumination to be somewhat close to a so-called white spectrum, in the first palce, perhaps shifted a bit. The spectrum you are providing is largely devoid of many color wavelengths that are in a white-ish spectrum. You are using the camera to do something beyond its design capabilities and something, quite frankly, that doesn't make a lot of sense in the first place.

 

What you are trying to achieve is a picture that 'looks good.' That means it is pleasing to the eye and may even reproduce something close to what your eye is seeing under the actinic illumination. That is specturm matching, not white balance. Your illumination spectrum isn't white. The way you must operate to capture the effect you want is simply trial and error and a lot of note taking. Some people call that experimental physics. You just have to 'find' what works under the different non-white spectrum illumination schemes you want to photograph.

 

When I dive, the world I am in is not white-balanced. Above about 30 feet of depth, between 10 am and 2pm, within about 25 degrees of the equator, on a sunny day it is nearly white balanced and I can use the sand bottom to white balance my images. When I am deeper, the spectrum doesn't shift to the bluer end, it attenuates the redder end. So now the spectrum doesn't even have a similar shape to a white spectrum; rather it is lopsided. If I want to reproduce what I see, I use the white balance from the real world, maybe from above the surface or from white sand at a shallow depth, if there is any. The images will come out very bluish, including the sand, just as I see it with my naked eye (through a mask). If I want color based on white-spectrum light, then I provide white-spectrum light and illuminate the subject. Now I can take a white object and white balance against it at depth to make the illuminated subject look 'right.' But as soon as I film without the illumination, my white balance is off to the degree my illumination is not really white-spectrum.

 

So you need to figure out what you want your pictures to look like, color-wise, and experiment to get as close to that as possible. Your illumination source determines the spectrum you are photographing within. If you are taking still shots and you want some kind of real white balance, use a flash or use two flashes. If you want to capture the irridescence (zoos under blue lights), don't expect your camera to do that automatically. You have to develop the knowledge ( or lookup table ) to set the shot up to achieve that effect.

 

fab

Edited April 28, 2007 by fab

[Rascal]

Thanks. That makes sense. I have started a table to keep track of how things come out with various settings, and it has really helped.

 

As far as colors go, my goal is to take pictures that accurately reflect my tank as it appears to me. My full lighting shots are getting a little bit closer - although the colors are still not nearly as vivid -- but I still haven't even begun to come close when it comes to actinic shots. What seems to really be lacking is the florescence that "pops" under the VHOs, especially the greens.

[fab]

Good for you. A methodically maintained notebook will outstrip a lifetime of undocumented anecdotal experiences any day. I hope you succeed!

 

There is a possiblilty you may have to use film to capture that look accurately and vividly. I recommend you go to a professional photographers' store and discuss with them what it takes to capture irridescence. You might need a film that is especially faithful in the deep blues. Ask them whether your ccd camera should be able to pick up these colors accurately. Another thought is to call Canon customer support and discuss it with them. I've had good luck with the camera companies' tech support for questions like yours. You are trying to do something that is off the beaten track in photography.

 

BTW, if you do use film then use positive (slide) film, not negative film for prints. You will get your best color saturation. Get professional advice on which brand and specific model of film. The brands are substantially different from each other in how they render colors. My guess is that Fuji will end up being the better choice for what you are trying to capture. Kodachrome is usually toned down. Fujichrome is usually toned up, yielding very vivid colors with excellent color saturation. It is popular with underwater photographers for this reason.

If you finally get a couple of really good pictures, you can get them scanned into digital format.

 

Keep us posted on your progress. What you are trying to do is not easy.

 

good luck,

fab