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03-12-2012, 06:41 AM   #1
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K5 sensor with Cokin ND Grads

Hi there,

last year I went on a photo course up in the Lakes with my K20D. Lotys of pics had a pronounced pink cast when using over ND8 grads. I have since found out that it is the IR light not being stopped by the grad that is getting throught the sensors IR filter.

Does anyone know if the K5 is affected by this as it seems to be dependant on camera type. My K10D isn't affected for example.

Cheers - Bill

03-12-2012, 06:56 AM   #2
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Were they Cokin original ND grads or eBay ones (the Chinese eBay cokin filters are notorious for colour issues
I haven't noticed anything serious with my Cokin on the K7, that being said the Lee filters and thor labs filters are better (and more expensive) than the Cokin filters
Definitely if ir is the culprit different cameras will perform differently as the strength of the ir cut filter varies
Singh Ray who also make good filters have this in their faq's

QuoteQuote:
Q13) I'm getting a color cast with my Neutral Density filter. What's the problem?

A: When using a Neutral Density filter (graduated or solid) you are generally causing your camera to make a longer exposure than normal, sometimes much longer. The software in some digital cameras uses response curves that adjust the RGB sensors sensitivity based on the exposure time, which may introduce more red into the image. Sort of a digital form of reciprocity failure. In other instances, blocking visible light and a longer exposure allows infrared light to "build up" on the red sensors leading to a red or purple-ish cast. If your filter looks neutral but you see the cast in your images, try taking some test shots using the filter with a different brand of camera, or with a film camera. If you still see the cast, and you're within the warranty period, contact Singh-Ray to have your filter evaluated and possibly repaired/replaced.
03-13-2012, 03:13 AM   #3
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QuoteOriginally posted by eddie1960 Quote
Were they Cokin original ND grads or eBay ones (the Chinese eBay cokin filters are notorious for colour issues
As far as I know they are original, although I did get them from e-bay but not from China directly. I don't remember seeing any issues with my K10 using them but I can not remember if I was stacking them or not.

I am considering some Lee filters as I like being in debt!

Bill
03-13-2012, 06:01 PM   #4
DAZ
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More than likely the “pink” cast is due to like leaks. When you use a strong ND than any other light becomes a major source of light. The biggest is from the view finder. This is why Pentax (and every other camera company) gives a cover for the view finder. The next biggest source is can be around the filter. If you are using the Cokin filter system light can get in the top and bottom. It then is reflected between the filter and the lens or any other filter. To block this you need something absolutely opaque to light like aluminum foil. Cinefoil is perfect for this as it is flat black and thicker.

DAZ

03-14-2012, 09:18 AM   #5
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QuoteOriginally posted by DAZ Quote
More than likely the “pink” cast is due to like leaks. .
Possibly, Hi Tech gave me today the same answer as above re the IR leaking.

Anyway, in a fit of spending I have today gone the Lee route of 0.6 and 0.9 hard grads so either it will be a master stroke, or an expensive mistake!!!
03-14-2012, 09:25 AM   #6
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QuoteOriginally posted by Billgscott Quote
Possibly, Hi Tech gave me today the same answer as above re the IR leaking.

Anyway, in a fit of spending I have today gone the Lee route of 0.6 and 0.9 hard grads so either it will be a master stroke, or an expensive mistake!!!
The Lee's are excellent filters, so are the Tiffens (Tiffen is widely used in the movie industry for colour balancing film stock)
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