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DPChallenge Forums >> Tips, Tricks, and Q&A >> Canvas-like texture on infrared images
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Nikon D800
01/19/2011 04:43:38 PM · #1
I've had my Nikon D100 converted to infrared and on occasion, I get an image that looks like it has the texture of canvas underlying the image. I've compared the meta-data of good, smooth images and the shutter speed and f-stops are the same; the only difference I can see is the smooth ones I looked at were shot at ISO 200 and the canvas-like textured ones are shot between 400-500 ISO. It's not noise...it looks like "lines" across and up and down on the image. Are there any infrared shooters out there that have seen that weird texture before? Do you think it could be ISO or is something else going on? Thanks for any thoughts you might have.
Canon EOS-5D Mark IV
Canon EF 24-105mm f/4.0 L IS II USM Lens
 01/19/2011 05:31:35 PM · #2
Sounds just like a moire pattern. "Most current digital SLR cameras incorporate the Anti-Aliasing Filter (AAF) with the IR cut filter in a 3 glass sandwich. When a converter removes the ICF, the AAF is also removed." Read more here.
Nikon D800
01/19/2011 06:27:38 PM · #3
Hmmmm, I'm not sure that's it. The pattern occurs on landscape images which would would be contrary to the statement from the link as follows. "Aliasing occurs when the visual pattern from the image matches a multiple of the spacing of the pixels on the sensor." It's especially pronounced in the clouds or flat areas like fog.
Canon PowerShot S3 IS
Canon 12x IS USM (S3 IS built-in Lens) -- 36-432mm (35mm EQ)
 01/19/2011 06:36:03 PM · #4
You may need to do some experimenting to see if there's a pattern (pun intended) to this problem. I'd suggest finding a scene which creates the problem and one which doesn't, and at each site, shoot the same scene using each of the ISO settings at several aperture settings and at several zoom levels (or with different lenses) to try and isolate the problem to either the electronic or optical system.

You could shoot in Aperture-Mode if you want to compare "good exposures" or in full Manual if you don't want to add the additional variable of shutter-speed to the test images.

You might also post some 100% crops of samples which show this problems so we can see what it looks like -- your description is way shorter than a thousand words ... ;-)

Message edited by author 2011-01-19 18:37:37.
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