Color Correction Filters

[Photo Dave]

Hello All... I'm inquiring about filters to correct color shift during long exposures. Long as in Hours! My latest project is star trail photography such as the attached image.

The film manufactures recommend filters to use for their films to correct color shift during long exposures but they are only talking seconds not hours. I picked up a copy of The Complete Tiffin Filter Manual, it's really excellent but I'm confused about Primary, Secondary and Complimentary colors, and how they interact with each other. And more importantly which filters will block or pass what color. If I'm interpreting the book correctly wouldn't a cyan filter adjust the magenta out to give me a more "natural" looking image? Though I'm not sure what natural is exactly!

This image is a 4.5 hr exposure @ f8 on Provia 100 film. And on a related note... Which film would work best for this? I rummaged in the back of the frig and came across this Fuji 35mm which I'm experimenting with, dialing in F-stops and exposure times, before I start to burn the Expensive stuff. I've always heard Fuji is a "cooler" film with a blue cast while Kodak film is "warmer" so they will react differently. If anyone has experience with this technique I'd sure appreciate your comments... you'll save me a lot of time and money experimenting.

Thanks... Dave

[Gordon Moat]

I found sort of the opposite between Kodak and Fuji, though I have not shot Provia. Specifically I find that E100VS shifts more blue over time, and Velvia 100F goes more magenta (actually one of the reasons I no longer use that). Normally I use nothing stronger than an 82B with E100VS, and often only an 82A. I think you could try either of those with Provia, based upon your attached image, and stay away from a too strong blue 80A.

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

[Walter Calahan]

Or try a modern color negative film. I realize that many can't part with transparency film, but sometimes with extreme exposures and color shifts, color neg is easier than trying to nail the right filter correction.

[CG]

Probably not too many people are doing exposures as long as you need, but you can sort out your filter needs by testing

Maybe you could do test shoots at the times you need. One shoot will give you the general direction your filters will need to go. A second shoot with a guestimate filter will get you closer. It's a iterative process that will bring you to whatever level of accuracy you need with a few cyles of testing and refinement.

Best,

C

[panchro-press]

You might check with astronomers. I never did any photo-astronomy myself, but I recall they would do some crazy stuff to compensate for colour shifts in long exposures.