[Leica] IR Filters; Rain and Sun

[henningw at archiphoto.com (Henning Wulff)]

>Does this still occur if you do not use auto White balance?
>Henning Wulff wrote:
>>
>>I think you will find that the center of the image is more magenta 
>>than the corners. This has been referred to as a 'cyan drift'. The 
>>central magenta look is actually correctly filtered but looks 
>>magenta because the auto WB averages things out, and the cyan 
>>corner conditions are the result of the oblique rays filtering not 
>>just IR but also visible magenta. This effect can be corrected in 
>>software, whereas the IR sensitivity can't.
>

I'm quite sure it would; if you look at the filters at a steep angle, 
you'll get a cyan cast. It's a radial effect due to the incident 
angle, so the center would still be balanced correctly, but not the 
edges. With digital it's easy to corrected with the radial luminance 
correction tool in panotools, but that tool doesn't come with Velvia. 
So for wideangle lenses, take off the filter.

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>Harrison McClary
>Harrison McClary Photography
>harrison@mcclary.net
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>
>
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