Weird Color Shift w/NDs

E

earmarkcreative

Active member
On a recent shoot, I got a really odd color shift when using ND glass filters in a matte box on the HPX500. I tried everything, black balance, white balance, changed the scene files, changed lens (I tried with both a canon and fujinon) we tried different brand filters (Tiffen + Schnider), SAME PROBLEM each time. We then tried the filters on an HVX200 and got the same problem.
We tried it on an HDX900 and voila, no problem. After some asking around, I found out that apparently the IR filters in the "lower-end" P2 cameras isn't that great (thus the prices I guess? ) The only solution is to use a pancro filter.

See the image below for an example. A few things to note when viewing the image:
1) The guy's sweater is BLACK! His cap is red so fairly accurate to what you see here.
2) Its not a white balance issue since there is no color cast and the grass is still green and there is a bit of blue in the sky to the top right.
3) I think an ND6 was loaded at this time.


I am just wondering if anyone else has had this problem with their HPX500. Panasonic Canada is currently baffled by this discovery too. They are working very hard to recreate the shooting scenario to get to the bottom of this.
 

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smelni:
Have you experienced the issue with your HPX500?

Hunter:
We tried with both Tiffen and Schnider filters and got the same response. For the rest of the shoot, I used the built-in filter wheel.

What's a hot mirror?
 
"Hot" IR mirrors block IR light (which is causing the color shift) sometimes when you use heavy ND, you block so much visible light that the IR light becomes more visible. A hot mirror goes in the first filter tray before the ND, but now there are hot mirror+ND combos for cameras sensitive to IR light (The Red camera)

pancro.com sells them.
 
i ahvent run into it on the 500 but that made just be circumstantial -

hunter - thanks for the tip - that makes a lot of sense
 
I see. Yah, I already figured out that pancro is the only way to combat the issue (see my original post) OR to use the on-board ND's.

Thanks
 
Sounds like an infrared issue. Sometimes with a heavier ND filter, more infrared light gets through in proportion to visible spectrum light and turns your blacks to red, if the camera doesn't have enough of a filter built in over the sensor. (oops...just as hunter richards mentions above.)
 
one question then - why do the internal ND filters not have this issue - are they IR coated?
 
I bet internal ND filters are very high quality. (speaking that they are less than the size of a quarter!) Maybe they are coated with some sort of mirror?
 
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