Hot Mirror Filters

Sean Lambrecht · October 28, 2008

A couple questions about hot mirror filters:

Are Interline Transfer CCD's affected by near infrared light, or is it only CMOS chips? I've read that CCD's are affected, but read somewhere else that 3 chip cameras are not...(?)

Are the ND filters with a hot mirror coating necessary, or would an individual hot mirror filter work in front of any grade ND as long as you don't stack multiple ND filters?

Michael Collier · October 29, 2008

All electronic optics are affected. Some more than others. In my experience I haven't noticed one being more sensative to it than the other. If you need anymore proof of their sensativity to infrared and near infrared, point a remote control at the lens and hit a button. if you see the LEDs light up in the viewfinder its picking up IR.

I think the reason this has come out recently as a problem, is DPs are far more likely to use ND than any other users of CCD or CMOS technology in video, and are prone to being more particular about their effects. ENG and EFP users don't really use ND, other than the built in ND filters in their camera (and usually not anywhere near in the ND9+ range common on daylight shoots we might do)

Heavy ND without a hot mirror will magnafy the effect. You might not see weird coloration with a certain camera, but throw an ND 1.2 on and you might. I would use one with any measure of ND if possible, but definatley over ND3 should have either a coating or a seperate mirror.

You can use a mirror with regular NDs (like you said, don't stack multiple NDs) the problem with this is the same problem with using too many filters. The optic track will be effected. If that flare artifact doesn't matter much to you, then go with it. If you don't like it then get the ND set with HM coating. Also consider if your ever caught in a situation where you need ND, Pola, 85b. Do you really want to add another peice of glass to take care of the hotmirror? Or will your matte box even allow for another peice of glass?

If your looking at getting a new set of NDs, I would get the mirrors, because it won't have an effect on your film work, but you'll be covered for video work. If your renting, maybe sometimes its cheaper to rent the hot mirror set only when you need hot mirrors.