UV problems - being turned into magenta/cyan by sensor

inasir1971

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I am currently living in Bangkok and we have a lot of sun in the day. To give you an idea - I took a shot yesterday ISO 200 f8 with 9 stops of ND filters (3 Hoya ND8's) and exposure time was 1/45 s - there is so much light that I can AF perfectly through the 9 stops of ND filters.

Using Canon 7D and 550D with various lenses. I shoot RAW and convert. I was getting some cyan/magenta on the edges of objects and had previously attributed it to lateral CA but for some reason I could never eliminate it. Going back over some previous shots (white flowers etc.) - I think that UV was the issue.

I wanted some more color in the sky and tried recovering highlights for the first time, they were huge patches where clouds were turning pink/magenta and cyan - what I previously thought was CA was actually reflected UV being transformed by my sensor into magenta/cyan. I know people say you don't need UV filters on digital and for the most part I agree and shoot with a B+W MRC 007 (Clear) protector.

Suspected it was UV and switched to a UV + Haze - it helped a bit (I think). To test I then added stacked a second UV + Haze and that almost eliminated the problem but not fully. There must be a better solution than stacking two or three UV filters?

Any ideas / recommendations?

Thanks in advance everyone
 

tirediron

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Many ND filters can impart a magenta cast on an image, especially if you're shooting toward the sun.
 
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inasir1971

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I wasn't using any ND filter (just a B+W MRC 007 Clear) for the problem shots. My apologies - I should have been clearer about that.

I only mention the ND filter to give you an idea about the amount of light present in the day (and presumably the amount of UV).

Thanks for the input.
 

Garbz

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It's not UV. Between the sensor's lack of sensitivity in the UV range, the UV blocking properties of glass used in most lenses, and the UV filter on the front of your camera there would be no UV recorded.

I live right below the Tropic of Capricorn and our UV index is extreme pretty much every day of the year. Yet your problem is one I've never heard of. If it were something as common as UV there'd be many complaints and many knowledgeable solutions as well.

Can you post an example?
 
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inasir1971

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Done better - I've uploaded the original CR2 files as well as processed JPEG's into my public folder on iDisk (no password). Accessible by browser on:

https://public.me.com/inasir1971

Shots taken spot metering on subject.

I think access to the full RAW file would be more helpful. Problem really appears when you try highlight recovery. I'm stumped as well...


Thanks everyone
 

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