jcolwell
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 IR mods | |
I've recently been playing around with some DSLR's and a Wratten 87 filter. I was quite surprised to find that my 1DII is very sensitive to IR light; the 20D is a bit sensitive, and the 5D less sensitive. The 1DII with 87 filter has probably about the same sensitivity as Kodak HIE film with the same filter, from what I recall (it's been a long time).
The first attached photo is a 1DII test shot from yesterday with Wratten 87 on 50/1.4 at f/2.8 and 1/2 sec, ISO 800; taken handheld from my bedroom window, on a windy day. Not a "keeper", but it suggests that the unmodified 1DII has real possibilities.
As for which filter to use, the second attached image is a screen shot of a spreadsheet I recently put together. It shows IR filter transmission properties for Wratten 29, 89B and 87 filters, with a colour bar along the bottom to show the visible spectrum. The slender, vertical blue lines show wavelength at 50% transmission for each filter. The 50% wavelength for the Wratten 87 is about 790 nm, and that for the 87C you mentioned is further to the right, at about 850 nm.
I have a 89B filter on order to see what I get with a bit more red in the picture (if you'll pardon the pun), but I'd hesitate to go lower wavelengths for "IR" photography. The 87C is more completely in the IR range, with no visible light passed at all.
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