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09-09-2010, 09:20 PM   #1
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Km IR filter cut-off

Hi all!!

Does anyone know at what wavelength the IR filter in front of the sensor cuts in? Anyone have a specta for the filter?

Cheers,
Mario

09-10-2010, 09:00 AM   #2
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There are 720nm and 900nm filters, the former being the more common, AFAIK.

Edit: are you referring to the filter on the sensor itself rather than that on the lens? AFAIK, the one on the sensor cuts away all IR wavelengths. It will have to be removed if you want to do true IR photography.

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09-12-2010, 09:22 AM   #3
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Various IR-pass filters are available. I use 780nm, 900nm, 930nm and 1000nm filters on my 5mpx Sony DSC-V1 'NightShot' P&S, which has a switch to flick-sway the IR-blocking Hot.Filter. If you want to do serious IR work with your Km, you can have the Hot.Filter surgically removed and replaced with clear optical glass. You can then use an IR-blocking filter in front of the lens for general photography, or any IR or other spectrum-slicing filter for specialized work. Remember than sans a Hot.Filter, the vast majority of digicam sensors are sensitive to IR and insensitive to UV.

But to answer the question: Hot.Filters usually have a sharp cutoff at 700nm.

Last edited by RioRico; 09-12-2010 at 09:34 AM.
09-12-2010, 01:20 PM   #4
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Thanks for the info.

I was after the cut-off for the ir filter in front of the sensor. I'll put it at around 700nm meaning that I should be able to get decent information at around 656 nm (hydrogen alpha in astrophotography).

Cheers,
Mario

09-12-2010, 01:26 PM   #5
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Not a lot of info that I have been able to find. From what I seen, the cut-off is around 700 to 750 nm.
http://www.samirkharusi.net/spectrograph
This site is astro, not specific to pentax but gives an idea.

Last edited by Ex Finn.; 09-12-2010 at 01:32 PM.
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