Dark Frame Subtraction

NRV Shooter · 12-25-2012, 06:39 PM

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.

**ismaelg** · 12-25-2012, 07:10 PM

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,

**interested_observer** · 12-25-2012, 07:33 PM

NRV Shooter · 12-25-2012, 07:43 PM

Originally posted by ismaelg

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!

MPrince · 12-26-2012, 10:58 AM

Originally posted by NRV Shooter

...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.

NRV Shooter · 12-26-2012, 03:38 PM

Originally posted by MPrince

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.

Dr_who · 12-26-2012, 03:58 PM

Originally posted by MPrince

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.

MPrince · 12-26-2012, 04:40 PM

Originally posted by Dr_who

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.

lister6520 · 12-27-2012, 10:25 AM

Originally posted by Dr_who

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.

Dr_who · 12-27-2012, 10:27 AM

I just have it turned off fully. If needed I'll take my own dark frames with lens cap on

12-25-2012, 06:39 PM	#1
NRV Shooter Senior Member Join Date: Feb 2010 Location: New River Valley, Va. Posts: 116	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, 07:33 PM	#3
interested_observer Loyal Site Supporter Join Date: Jun 2009 Location: Tumbleweed, Arizona Photos: Gallery \| Albums Posts: 5,707	Dark-frame subtraction - Wikipedia, the free encyclopedia Dark Frame Subtraction using Adobe Photoshop<br>by Chris Limone \| Take Great Pictures JPEG Dark Frame Subtraction Dark Frame Subtraction Guest post: Dark Frame Subtraction \| Nikon Rumors Astromart Articles - How to Subtract Dark Frames with Photoshop, Photoshop LE, or Photoshop Elements Dark frame subtraction Dark Frame Calibration Dark Clear Skies: Why Subtract Dark Frames?

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12-25-2012, 07:10 PM	#2
ismaelg Loyal Site Supporter Join Date: Apr 2009 Location: Puerto Rico Photos: Gallery Posts: 2,681	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
NRV Shooter Senior Member Join Date: Feb 2010 Location: New River Valley, Va. Posts: 116 Original Poster	Originally posted by ismaelg 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
MPrince Veteran Member Join Date: Sep 2006 Location: WV Posts: 1,495	Originally posted by NRV Shooter ...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
NRV Shooter Senior Member Join Date: Feb 2010 Location: New River Valley, Va. Posts: 116 Original Poster	Originally posted by MPrince 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
Dr_who Veteran Member Join Date: Jun 2009 Location: Edmonton, Alberta, Canada Photos: Gallery \| Albums Posts: 777	Originally posted by MPrince 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
MPrince Veteran Member Join Date: Sep 2006 Location: WV Posts: 1,495	Originally posted by Dr_who 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
lister6520 Veteran Member Join Date: May 2012 Posts: 733	Originally posted by Dr_who 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
Dr_who Veteran Member Join Date: Jun 2009 Location: Edmonton, Alberta, Canada Photos: Gallery \| Albums Posts: 777	I just have it turned off fully. If needed I'll take my own dark frames with lens cap on