A hot mirror is a little different from an IR filter, but the purpose is the same.
A hot mirror filter has a coating on the outside of the glass that reflects IR light. The filter needs to be the outermost piece of glass, and the coated side needs to be on the outside.
A regular IR filter is integral to the glass, rather than being a surface coating, at least the few I’ve seen.
We’ve been using a Hot Mirror/1.2 ND combination for our Red camera, since the IR pollution only seems to show up around N9 or so. It’d be great to have one at .9 and one at 1.2, but they ARE expensive.
Red Camera Rental & Indy Features, Denver Colorado.
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