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07-19-2010, 08:10 PM   #1
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K-x and Infrared

I recently picked up a 720 nm IR filter, and have been experimenting with it. My biggest problem is exposure. Just how red are my pics supposed to be (pre-processing)?

So far, as an example, on sunny days, I can get satisfactory (to me, anyway) photos using my 55-200mm of 1/2, 0.4, 0.3, 1/4, & 1/5 sec, @F5.6, 115 mm. On cloudy days I seem to be upping that to around 1-3 seconds.

Anyone else trying IR that can share some information?

07-19-2010, 08:28 PM   #2
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The rule of thumb I got from somewhere and have been using is that looking at the histogram, it should look slightly underexposed (the curve peaking towards the left of center).
07-20-2010, 07:52 AM   #3
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I found a good reference for how pics should/can look using filters is the Cokin site. www.cokin.com
07-20-2010, 05:58 PM   #4
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All should be red, you are mainly letting in the long=red wave lengths, heavy pp is normal.

07-20-2010, 06:49 PM   #5
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I don't know about the K-x, but the K100DS has a really weak IR filter, and I do 4-8 seconds in full noon sunlight to get good exposures.

You want to get the histogram as far to the right as you can without blowing out the red channel. If you underexpose at all, you'll be amplifying noise in all the channels when you process.

Everything will look red because the filter removes everything above 720nm which is deep red, into near-IR. You can either go B&W, or swap the red and blue channels (there are tutorials online) to get blue skies back. You can also get funky color effects by setting custom WB off various tones in the picture.
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