Why is there a GREENISH GLOW around the Subject ??

[George D.]

I have run into a small problem, so I'd like to get some opinions on what the solution might be.

I think I know what it is, but the insight of others is important to me, so feel free to comment.

I have been doing this kind of thing for many, many years, but have not run into this situation before.

We have been shooting a subject in an aquarium filled with water. We're using a still SLR macro lens on our Red-One Camera. The aquarium glass is 1/4" thick, and the subject is approximately 11" behind the glass.

When we look at our subject on the PC screen during post production, it seems to have a greenish glow around the "outside" edges. This could be due to the glasses color, since, like most glass, it has a very, very slight greenish color to it, or to the thickness of the glass itself.

But, it could also be due to a lens problem, causing color aberrations. It is a very high quality lens, but it is old, so that is also a consideration.

What do you think?

Thanks for your time.

George

.

 

[Nick Pasquariello]

This could be caused by . . . a lot of things. However, it's almost impossible to guess without seeing a screengrab. I could be talking about some spill, or some reflection, or some lens aberration . . . without seeing it though, that's the closest guess I can make.

 

[George Butterfield]

The green areas are green because they are receiving green light. This could be because of an aberration or from a genuine green light source. Try the exact same shot without the water if possible. The water could be acting as a prism. maybe try shooting thru full and empty glasses of water. (salt water if that is part of the mix). If the water is causing a prism effect maybe try moving the light sources. If you're using daylight, try tungsten or vice versa. Try a different lens. Personally I think it is diffraction. Try a different composition.

 

[Robert Hart]

My wild guess is the effect is more apparent with wide-angle lenses. The light which lands at the edge of image circle has to travel a greater distance through what is in effect a very-very thick planar optical element. If there is anything in the glass or glass-water combination to produce a green hue, then at the corners or edges this may be more apparent. If you view through the corner of an aquarium you will observe a prism effect on objects behind. The glow may become less apparent if you sit off from the subject with a longer lens. You might also need to consider a polariser filter as multiple reflection within the aquarium may be affecting the light. This will also guard against reflection from your side of the aquarium appearing. There might be a prism effect if your ambient light sources are cutting across the corners of the tank and reflecting off the rear wall of the tank. The same might happen because of several generations of internal reflection if you are adding light. Maybe try a small kicklight with Lee 1/8 or 1/4 Minus Green gel aimed through the back of the aquarium - another wild guess. - PLease heed the advice of those wiser and more qualified than I.

 

[Jeff Whitehurst]

My hunch is that your aquarium is made with "soda lime" clear float glass which is producing the green color. "Low Iron" or "Water White" glass is what you need to shoot through for best results.
http://www.truaqua.com/high-clarity-aquarium-fish-tanks.html