I photograph clothing in a studio with a Kodak DC 120 zoom and Lowel Tota lights and keep getting strange color casts on some of my images (especially noticable on all-black or all-white garments). It seems to be pretty random. Mostly, I get a magenta cast, sometimes blue, and an occasional amber. Does this sound like IR interference from "hot" lights? If so, what exactly are hot lights? Are they literally HOT lights, because these Totas are definitely hot. Finally, what can I do to correct? Money is a bit of a factor. Thanks Ben Burke

-- Ben Burke (benjaminburke@hotmail.com), January 04, 1999

Answers

Dont think that I.r. is the problem. Supposed I.R interference if it occurs will only be in near infrared range since Silicon has a sensibility as far as 1160 nanometers. If silicon sensors are not filtered from visible red (around 750 nanometers) to 1.160 5 you can have a "x-ray" effect, some colors, specially red become transparent. To make a test, draw something with a black pencil, then cover it with some red paint (not to thick film) if you will see the underdrawing then your camera is badly filter. A Sony video camera has this problem last summer.

-- Luc M. Comolli (Lucamax@bigfoot.com), January 06, 1999.

The single-chip Kodak color imaging sensors use a stripe filter which means your image is passing through colored plastic before it registers digitally. Sounds like a chromatic aberration. Maybe a ND, UV, Sky, etc... filter would help.

-- Jon (jonmiles@pacbell.net), January 08, 1999.

Do the color shifts reproduce reliably on the same subject, or are they pretty random? If the same behavior with the same subject, it sounds like a camera problem. If not, ???.

"Hot" lights refer generically to tungsten, and it can produce some wacky results, but usually the problem manifests as under-saturated color and excessive image noise. A (partial) fix is to use a Tiffen "Hot Mirror" filter over the front lens. These aren't cheap (typically $50 or so for a reasonable size, like 52mm). They don't completely cut out the problem, but do help.

Your problem though, sounds more like white-balance difficulties: Are there strongly-colored objects elsewhere in the scene with the complement of whatever color tinge you're seeing in the whites/blacks? (In other words, when you see a magenta tinge, do you have a bright green object somewhere in the scene?) If so, what's happening is that the subject is faking-out the cameras's auto white-balance algorithm. We've never tested the DC120, so I don't know the specifics of its white balance capability. Some cameras allow you to select a "manual" white balance option, which fixes the color balance at some unvarying standard, usually set for daylight, tungsten, etc. If you have that option, try the "tungsten" or "incandescent" white balance setting and see what happens. (An alternative would be to select "daylight", and us an 80A filter to balance the tungsten to a daylight color temperature. This won't work though, if the DC120 isn't doing its metering through the lens. (Again, don't know specifics, not having tested it.)

Hope this helps, report back what you find!

-- Dave Etchells (hotnews@imaging-resource.com), January 08, 1999.