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Old Jul 20, 2005, 11:03 AM   #1
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I posted these images along with color and grayscale versions of same image in the "Critiques and techniques" forum : http://www.stevesforums.com/forums/v...mp;forum_id=90

Since I got no response, I'll try here.

I purchased a Cokin P7 (Wratten 89b equiv) filter for my D100 and am trying to learn to use it.

The best technique I have found so far is to frame and focus the image without the filter, insert the filter and shoot (using tripod, of course!). I then split the IR image to RGB channels and discard the blue and green channels. I do a slight histogram adjustment (levels in PS??) on the red channel image and below is what I get. Is there a better way or is this method a good one?

IR image from camera:


Red channel from Split RGB:


Any comments good, bad, ugly, or constructive would Really be appreciated. Thanks for your time.

Cal Rasmussen

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Old Jul 20, 2005, 11:28 AM   #2
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It definitely has the look of an IR shot :-).

I bought the same p007 filter just haven't had any time to play with it yet.
Only thing I notice is my camera has no trouble focusing with the filter attached over an F2.8 lens. Nice but you never are sure what it actually chose to focus on :blah:

Peter.

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Old Jul 22, 2005, 10:59 AM   #3
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Thanks for your comments, Peter. It has always been my understanding that IR focuses differently than normal color or BW. If you look at the focus scale on your lens, you may see a letter "R" next to the normal focus line. In film, if you use IR film, you focus the lens manually. Then you look at where the focus scale lines up with the index mark. You then adjust the focus so that the point that was lined up with the index mark is lined up with the "R".

I don't think doing IR with a filter works the same way. With IR film, you capture both reflected IR and emitted IR from heat sources. With a filter, you only get the reflected IR. I don't know if this affects focus or not. It doesn't seem to. I have tried manual focus (focusing before inserting filter) and auto-focus. I got good results either way.

The real problem for me is how to post-process and get the best looking monochrome image. I have seen several techniques described but I can't seem to get any of them to work. The best result I have obtained so far is by splitting the IR image to RGB channels which generates three monochrome images based on the red, green, and blue values in the image. I find that the blue and green channel images generally contain nothing useable. However the red channel contains an image that seems to be usable but usually a little dark. I adjust the histogram to lighten it a bit.

My real question is -- Is there a better way?

Cal Rasmussen

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