Odd spot discoloration

[CeeScott]

Hey all, long time lurker but I had to register just to post this question. I searched the forum a few different ways and couldn't find any leads on the problem I'm having.

We are an auction house, and I have a setup I'm using strictly for coin photography. It's not all space-age top of the line, but 90% of what I'm doing looks great.

The camera is an Olympus TG-2, attached to a photo stand. I have a two-light setup running standard incandescent bulbs ("soft white") inside soft light boxes. I use a custom white balance, shot against a neutral gray card each time I start a session.

Here's an example of a silver dollar shot that looks as I would expect, and this is a typical result:

However, I'm noticing a troubling trend when I have a copper or darker toned coin. As you can see from the next shot, there is a spot of "pink" discoloration on Lincoln's head that looks like a discolored/worn/cleaned spot:

Moving the coin around so it's not centered demonstrates that the defect is not on the coin. You'll see in the following photo that Lincoln's face now looks fine and the spot has moved to the back of his head. I can actually spot the "pink" spot in the viewfinder if I move the camera around rapidly, I can watch the discoloration move around to whatever spot I'm pointing at.

Here's a really good example of the problem on another coin. None of that pink halo in the center is present on the coin itself:

This is driving me crazy, as it will negatively effect the amount that a bidder is willing to put up against a coin. My darker coins all look more spot worn than they actually are.

It's either not happening with lighter silver/gold coins or the effect is so faint that it's not a problem.

Things I've tried:

Making sure the lights are behind the plane of the front of the lens, so I am not getting any lens flare.

Going outside on a sunny day and shooting strictly with sunlight - the problem goes away and I cannot duplicate it.

Setting up the white balance to one of the defaults and shooting the coins with the wrong white balance. Problem goes away and I cannot duplicate it.

Swapping out lighting. Seems I can alter the effect for the better with lights of a different color tone, but I favor the over all color and clarity that I'm getting with this setup. CFC bulbs are just too blue, no matter how much I tinker with white balance. If this fixed the problem entirely, then fine, but I'm finding it only alters the effect.

So, awesome community people, are there suggestions for changing my set up? Do I have a faulty camera? Any thoughts you have would be appreciated, because I have 1600 lots waiting to shoot.

Thank you.

 

[JoeW]

My guess is that it's chromatic aberration. Usually you see this when you're shooting with a wide open aperture on some lens.

 

[astroNikon]

I love collecting coins

From what you mentioned the lights are even with the camera ??
Looking at your pics, your lights seem to be a various angles due to the shadows.
If this is a reflection and not chromatic abberation mentioned above You want light to bounce away from the camera, not towards it.

for example, if you use the oncamera flash you will get alot of glare. The further away at an angle you move that flash the less glare.
You have soft boxes so you can direct the light. The light should be generally at a 45 degree angle so directed light cannot bounce towards the camera.

read this - all 4 pages
Master The Family Of Angles | DigitalPhotoPro.com

by you moving the camera you are changing the angle of reflections so that hazy spot moves.
So move the lights to simulate the light angles from the camera movement.
You'll be able to find the best spot. usually 45 degrees from center.

you can also put a small cylinder under the coins to raise it from the background.

I'm sure someone is gong to recommend this book too
Light Science and Magic: An Introduction to Photographic Lighting: Fil Hunter, Steven Biver, Paul Fuqua: 9780240812250: Amazon.com: Books
but that link is a short version (really short) of it

 

[CeeScott]

Re: Light angles

I will check this out, but I would have to say that I've had lights all over the place while tinkering for a solution. They've been as steep as directly behind/above the camera pointing down, and as shallow as maybe 20 degrees and it hasn't made a difference for this problem. The discoloration remains fixed if the camera remains fixed, and doesn't seem to be moving around with the lights.

But I will double check this to see if I'm missing something there. Thank you!

 

[webrotate360]

Judging by your last image with a pronounced circular shape close to the center of the image, I'm guessing it's a reflection of your lens. You can try putting a small mirror or very reflective piece of metal instead of the coin and see what's reflecting at this exact spot.

 

[CeeScott]

I have had this happen with highly reflective coins, especially high mirror proofs.

However, the coins pictured above are almost entirely non reflective, but I like your idea of using a mirror to see what is reflecting at that spot. I will do so, thanks!

 

[KmH]

So the TG-2 is a waterproof camera?

If so I suspect there is a waterproofing window in front of the lens that creates an air gap and your pink spot is lens flare cause by that air gap.

 

[dennybeall]

If you look at the first photo you can see the spot is there on the ear. It's just not as noticeable as it appears a slight bluish tint around the ear. At least appears that way on this laptop screen. That definitely points to the camera in my mind and the air gap sounds like something that would cause the problem.

 

[Derrel]

So the TG-2 is a waterproof camera?

If so I suspect there is a waterproofing window in front of the lens that creates an air gap and your pink spot is lens flare cause by that air gap.

THIS ^^^^^ to the tenth power.

 

[godsotherson]

I had a similar spot occur when shooting a bronze bust a year ago and could not figure out the problem. Last week I took a shot while attempting to get extreme lens flare from the sun peeking thru foliage and got this image. Now I am convinced it is lens flare that caused my spot on the bronze as well.

 

[CeeScott]

Hey guys, just wanted to follow this up.

The suggestions that it was the waterproofing seem to be the cause. Through several different tests of lighting with this and another camera, I had to come to the conclusion that it's just a bad camera to use in this setup, which is really a shame! Everything else about the setup was easy to use and the other aspects of the coin photos were great, but it comes to naught if the camera discolors the final result.

I moved to a more expensive Canon EOS T5 setup and have resolved the issue.

Thanks all who responded with assistance!

 

[ruggedshutter]

Thanks for the followup. Glad to hear that you found and fixed the problem