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04-28-2012, 12:38 PM   #1
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Tungsten Front Focus - Possible Solution

I know this subject has been beaten to death, but I would like to share my experience on this.

My K-5 is clearly having the front focus issue under tungsten light, which is unfortunate. I happen to have a infrared cut filter (Hot Mirror like this one Hot Mirror Filters Press Release ) and put that on the lens to see what happens.
basically three things happen.

1 Its low tungsten light front focus issue is pretty much gone
2 Its low light focusing capability is significantly reduced (minimum light required to be able to focus is increased)
3 Lot more hunting as if it was much darker in the room under dimmed conditions

It was tricky to set the minimum amount of light that the camera would still focus with a IR cut filter on the lens while showing the front focus without the IR cut filter. I simply use the dimmer on my tungsten ceiling light to dim the room and then I shoot various subjects.

I have a feeling the issue is related to the IR sensitivity, however, my K10D does not show this problem, which is interesting.

From my IR photography I do, using a modified K10D, I know there is a focus shift when shooting IR, which is how I came up with the idea.

I just thought this is interesting, and hope the future K-5 replacement will not have this problem.


04-28-2012, 12:45 PM   #2

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Well, that's interesting. You listening Pentax?

Mental note: try out when camera received.
04-28-2012, 01:03 PM   #3
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Eric, did you happen to notice if the IR cut filter also helped reds and oranges from becoming oversaturated?
04-28-2012, 01:34 PM   #4
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Old news, ricehigh i believe already did this test.

found it with the Kr but that one uses the same AF.

Last edited by Anvh; 04-28-2012 at 01:43 PM.
04-28-2012, 02:40 PM   #5
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Merci ...

Thanks for your post ... always good to see solutions!

Salut, John le Frog

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