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12-25-2012, 06:39 PM   #1
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Dark Frame Subtraction

Can someone point me to an explanation of Dark Frame Subtraction? I have done the "search" thing here and think that it has something to do with long exposures, such as one might use in night photography. I have only seen it mentioned in reference to a K-7, in terms of it kicking in after 30 seconds of exposure. I have never seen it mentioned with any other Pentax camera, including the K10D which I use. Thanks.

If this thread is in the wrong forum section, please move it to the correct one and excuse my mistake.

12-25-2012, 07:10 PM   #2
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In simple terms, DFS works like this: If the exposure time is longer than x seconds (not sure how many, and I think it varies per model), after the shutter closes it takes another exposure of the same amount of time but without opening the shutter. Since it is in "total darkness", whatever is recorded in that second "image" is considered noise and it is substracted from the original shot. The idea is to eliminate unwanted things like overheated pixels etc.

Thanks,
12-25-2012, 07:43 PM   #4
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QuoteOriginally posted by ismaelg Quote
In simple terms, DFS works like this: If the exposure time is longer than x seconds (not sure how many, and I think it varies per model), after the shutter closes it takes another exposure of the same amount of time but without opening the shutter. Since it is in "total darkness", whatever is recorded in that second "image" is considered noise and it is substracted from the original shot. The idea is to eliminate unwanted things like overheated pixels etc.

Thanks,
Thanks!

12-26-2012, 10:58 AM   #5
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QuoteOriginally posted by NRV Shooter Quote
...I have only seen it mentioned in reference to a K-7...
If I am not mistaken, DFS in the K-7 differs from other Pentax models in that it cannot be disabled.
12-26-2012, 03:38 PM   #6
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QuoteOriginally posted by MPrince Quote
If I am not mistaken, DFS in the K-7 differs from other Pentax models in that it cannot be disabled.
I remember reading that somewhere which led to to see just what DFS meant. I don't think I will be involved with it much, based on what I have read in the responses. Thanks for the response.
12-26-2012, 03:58 PM   #7
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QuoteOriginally posted by MPrince Quote
If I am not mistaken, DFS in the K-7 differs from other Pentax models in that it cannot be disabled.
It can indeed be disabled in the K5, K5II and K5IIs. Possibly even on the K30.
12-26-2012, 04:40 PM   #8
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QuoteOriginally posted by Dr_who Quote
It can indeed be disabled in the K5, K5II and K5IIs. Possibly even on the K30.
It can even be disabled in the K100D. It's a mystery to me why it can't be disabled in the K-7.

12-27-2012, 10:25 AM   #9
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QuoteOriginally posted by Dr_who Quote
It can indeed be disabled in the K5, K5II and K5IIs. Possibly even on the K30.
Yes, it can be disabled on the K-30, and also the K-r.

You won;t find it by that name in the menus though. It is called 'Slow shutter speed NR' and can be set to auto, on or off.

When set to auto it takes into consideration ISO, shutter speed and the temperature of the sensor in deciding whether or not to shoot a dark frame.
12-27-2012, 10:27 AM   #10
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I just have it turned off fully. If needed I'll take my own dark frames with lens cap on
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