Slow shutter speed noise reduction k-3


BarryE

Link Posted 26/08/2014 - 08:47
There seems to be no real info on this in the manual and internet searches haven't shown any definitive data - as usual lots of conflicting opinions, so ...

Does "slow shutter speed noise reduction" on k-3 affect RAW images ? If so when does it kick in ? In the ISO NR there's control of ISO speeds where it's applicable, but not for shutter speed NR - just auto or off.

I had assumed that it was only applicable to JPEGs, however I've just tried some long RAW exposures (30sec) and they were surprisingly soft. (All the usual movement "lock-downs" were applied.) So NR got me wondering ... As the manual does not make an explicit mention of RAW/JPEG for NR, I've inferred that it does indeed apply to RAW.

Anyone got any knowledge on this ? I'm guessing there's some astro photographers out there who'll know ...

Thanks

alfpics

Link Posted 26/08/2014 - 09:28
I don't have a K-3, but slow shutter speed NR, AFAIK, means that any long exposure will be followed by another exposure of the same time. Ie the camera would be unusable for that extra duration as the sensor records a dark image that it then subtracts form the picture exposure. You would certainly notice whether the camera was doing that!
Andy

BarryE

Link Posted 26/08/2014 - 11:24
Thanks Andy for quick response.

I tried 20 sec exposures with/without NR in JPEG and RAW and the shutter was open for approx 20 secs in each case. So maybe K-3 is different or I don't understand what you meant.

Cheeers

alfpics

Link Posted 26/08/2014 - 11:50
If its like some of the other cameras, I suspect that NR only kicks in with a shutter time of greater than 30 seconds - ie try using B mode and, say, 40 seconds with NR activated
Andy

BarryE

Link Posted 26/08/2014 - 12:14
Thanks again, Andy.

The taking longer is, I assume, the processing time. Maybe I'll not really see it unless I accurately time and compare the shot times, as the K-3 processor is quicker than previous generations.

A quick Bulb test with NR on for >30 secs did not show any appreciable lapse after the shutter closed before it was ready to take the next shot.

Maybe the test I need to make is to actually compare the images closely for various settings. I was hoping to avoid this, if I could get a definitive answer. Got to get back to work now

It's a shame Pentax don't define functions like this ...
Last Edited by BarryE on 26/08/2014 - 12:32

JAK

Link Posted 26/08/2014 - 12:37
Have a look at page 42 of the manual which deals with noise reduction and the settings options.
John K

alfpics

Link Posted 26/08/2014 - 12:45
Ok - in the K5ii menu on 3rd page of 'camera' folder there is the slow shutter NR selection and I can select auto/ on/ off. It seems you might not have the always 'on' selection. If I select ON, then it always takes a double shot, the second being the nr (or dark field subtraction) shot, and the time = that of the first shutter time. And works on RAW files. So you would have noticed that, even though the processing time of K-3 is quicker!

As your shots seem soft, it maybe something else, as assuming everything is stable, the NR simply subtracts any pixels that are bright when they should be dark.
The high ISO nr is something that can make an image soft.
Andy
Last Edited by alfpics on 26/08/2014 - 12:47

BarryE

Link Posted 26/08/2014 - 13:31
JAK wrote:
Have a look at page 42 of the manual which deals with noise reduction and the settings options.

p42 is high I so not slow shutter that I can see ...

BarryE

Link Posted 26/08/2014 - 13:43
Andy, that's helped. NR auto was not applying any NR at 20 sec exposures. Setting it to ON applied NR function - could see NR in the top LCD display.

So the question remains, when in auto does it decide to apply it ? Anyway I can now see the function being applied so can experiment without having to laboriously check the the images.
Many thanks,
Barry

alfpics

Link Posted 26/08/2014 - 14:12
I think in auto it kicks in at exposures above 30sec
Andy

JAK

Link Posted 26/08/2014 - 14:25
What makes you think a long shutter speed affects noise reduction? I'm pretty sure it is only a high ISO that causes it to kick in if the camera is set for it to do. A long shutter speed with a low ISO would have little, if any, noise to reduce, so why would it need to be applied?
John K

alfpics

Link Posted 26/08/2014 - 14:32
There are two forms of NR that can be applied; high ISO and long shutter time. The long shutter time one removes the effect of pixels getting hot and bothered by a long exposure; ie some get 'hot' and this can happen at relatively low ISO as well. the K-7 doesn't allow you to turn it completely off and it always comes on at anything over 30seconds.
OTOH, High ISO nr is there to help reduce the random noise signal that a sensor has when you are applying a high level of amplification to it to get the high ISO performance. Hope that makes sense!
Andy

JAK

Link Posted 26/08/2014 - 14:44
This may be of some interest, though the writer is commenting on use of a non Pentax DSLR but no doubt things aren't that different.

http://www.kadamsphoto.com/nightphotography/long-exposure-noise-reduction/
John K

BarryE

Link Posted 26/08/2014 - 15:13
Hi John, that article helps with some detail. My inclination is to now have shutter nr set to auto (default) as it shouldn't degrade the image - just take double the time to operate - not sure when it does actually come into play, though.

High iso nr is another matter. I'm now inclined to set this to off and fix in post as this noise isn't predictable and so a visual fix is likely to be better, albeit taking longer.

Time will tell if this works for me ...
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