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04-14-2022, 11:04 AM   #1
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Noise in long exposures - K-5 vs K-3

I didn't quite see an exact answer in search for this so apologies if my search skills are just weak! I know the K-3 is touted for it's built in astro-tracer capabilities for long exposures on celestial objects. I'd like to try my hand at long exposure photography with my K-5 and am curious if the K-3 is better at maintaining a lower temperature on the sensor, and thus lower noise level, when the shutter is left open for time spans over hours in bulb mode with consecutive exposures.

I'm loving the high ISO performance on the K-5 and thinking now that a K-5iis makes the most sense as a second body. Despite the age the build quality seems to not slow these down.

Thanks in advance for pointers and sharing of experiences.

Cheers

04-14-2022, 01:03 PM - 2 Likes   #2
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I have a K-3II & one thing that I've noticed is that the edges of the sensor seem to shift to magenta when doing more long exposure high ISO photography. It starts happening even as low as 30 seconds in ISO 6400. I guess it starts getting hot inside the camera.

Here are a couple of examples of the K-3II at ISO 6400 shot for 30 seconds. You can see the image shifting towards magenta. I didn't use the GPS in these photos. I was just messing around.





When I use the GPS & a lower ISO in the K-3II for about 3 minutes or so, the sensor doesn't shift towards a magenta color at all. I haven't tried a several hours long exposure at low ISO, but I'm going to guess that it would be OK. It would probably explode at ISO 6400, though. Hahahaha!
04-14-2022, 01:34 PM - 2 Likes   #3
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IMO K-5 has very good sensor for long exposures, I remember there were some noise profile pictures on photonstophotos.com and K-5 was rated very good.
Example: night infrared, 12 min. exposure. Some white dots appear, but I did not use long exposure noise reduction
04-14-2022, 02:36 PM - 4 Likes   #4
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If you are really concerned about sensor heat artefacts then the thing to do is to take several dark frames at the same ISO and shutter speed at the end of your astro imaging session. From there you load them into your stacking program and tell it they are dark frames and it will create a master dark to subtract from all of the light frames. By taking multiple dark frames and averaging them together it removes more of the true random noise in the master dark providing a more accurate representation of the actual systematic error you want to subtract out of each of the light frames and thus final image. This method provides better results than the high ISO or slow shutter speed noise reduction as it allows you to capture more light frames in a given period of time and you also remove more of just the systematic error from each light shot. I prefer to capture as many light frames as possible when out so for capturing dark frames I do it at the end while I am tearing down and packing everything else up. So for each camera I usually get 15-20 minutes of dark frames (30-60 darks per camera).

04-14-2022, 05:23 PM   #5
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Great responses, thanks all. Sounds like K-5 is plenty robust for this kind of work.

The magenta color cast at higher ISO is probably an issue for any modern, high pixel density sensor. Gotta be careful with that gain!

That begs the question, though: what's base ISO for K5 and K3?

Beautiful IR shot, Medex.

Cheers
04-14-2022, 06:24 PM   #6
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QuoteOriginally posted by DeepSchwartz Quote
Noise in long exposures - K-5 vs K-3
This question was bandied around at length after the K-3's introduction. My memory is that the K-3 may have more more noise for combinations of ISO and subject, but that detail capture is generally better on the K-3. For direct comparison, K-3 noise performance is equivalent to the K-5 series cameras when the K-3 image is downsized to 16 megapixel.

As for my personal practice, I own the K-3 and address potential noise issues the same as I would on any other camera. I don't push the envelope and expect miracles nor do I do much NR in PP (I don't own dedicated NR software). Below is an ISO 6400 example...



One can click through to view higher resolution at Flickr.

Same evening, same subject, wider view...ISO 200



QuoteOriginally posted by DeepSchwartz Quote
hat begs the question, though: what's base ISO for K5 and K3?
Nominal base ISO for both cameras is ISO 100. Rumor is that it is actually ISO 200 on the K-3. I generally shoot my K-3 at 200.


Steve

Last edited by stevebrot; 04-14-2022 at 08:04 PM. Reason: Added second image for ISO 200
04-14-2022, 10:52 PM   #7
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QuoteOriginally posted by DeepSchwartz Quote
Great responses, thanks all. Sounds like K-5 is plenty robust for this kind of work.

The magenta color cast at higher ISO is probably an issue for any modern, high pixel density sensor. Gotta be careful with that gain!

That begs the question, though: what's base ISO for K5 and K3?

Beautiful IR shot, Medex.

Cheers
For long exposure I used ISO 80. What is worth to consider is K-5's antialiasing filter. I would go for K-5IIs model which has not AA filter - better details (my infrared camera is modified and has not AA filter)

04-18-2022, 11:39 AM   #8
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QuoteOriginally posted by Medex Quote
For long exposure I used ISO 80. What is worth to consider is K-5's antialiasing filter. I would go for K-5IIs model which has not AA filter - better details (my infrared camera is modified and has not AA filter)
A K-5iis is indeed high on my list. Less so after my experiment.

I tried a few 30s exposures at iso 1600 and iso 100 last night in the house. Results are good at 1600, even with strong shadow recovery in post using the built in NR. I'm continually surprised at how good the sensor is for it's age.

---------- Post added 04-18-22 at 11:49 AM ----------

QuoteOriginally posted by stevebrot Quote
This question was bandied around at length after the K-3's introduction. My memory is that the K-3 may have more more noise for combinations of ISO and subject, but that detail capture is generally better on the K-3. For direct comparison, K-3 noise performance is equivalent to the K-5 series cameras when the K-3 image is downsized to 16 megapixel.

As for my personal practice, I own the K-3 and address potential noise issues the same as I would on any other camera. I don't push the envelope and expect miracles nor do I do much NR in PP (I don't own dedicated NR software). Below is an ISO 6400 example...



One can click through to view higher resolution at Flickr.

Same evening, same subject, wider view...ISO 200





Nominal base ISO for both cameras is ISO 100. Rumor is that it is actually ISO 200 on the K-3. I generally shoot my K-3 at 200.


Steve
Cracking shot of that bridge.

I know that measured and declared ISO is a contentious subject in some circles. I'd expect that Pentax is maybe a bit more accurate than others, based purely off of my newfound brand allegiance bias. :^)
04-18-2022, 03:29 PM   #9
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QuoteOriginally posted by DeepSchwartz Quote
I'd expect that Pentax is maybe a bit more accurate than others
Yep...Standard Output Sensitivity (SOS) traceable to 18% gray.


Steve
04-30-2022, 01:01 AM   #10
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I have a K-3II and a K-5II. In terms of image quality the K-5II is much better.
04-30-2022, 03:20 PM   #11
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QuoteOriginally posted by DeepSchwartz Quote
I'm loving the high ISO performance on the K-5 and thinking now that a K-5iis makes the most sense as a second body. Despite the age the build quality seems to not slow these down.
I bought both new, the K-5 after the price came down to reasonable, which did not take all that long. The K-5 IIs after the arrival of the K-3, so I got it at 1/2 price in a left-over new stock closeout deal. I reasoned then I'd have one with and one without the AA filter. The K-5 IIs also had the AF upgrade, which was beneficial for some of my lenses. I also found fine detail to be better in many images. Of course, thereafter none of the new Pentax models had the AA filter, but substitute system that can be switched in as needed, a unique and brilliant solution. I went on to get the K-S2 as my small, lightweight model, then the excellent KP, but I still enjoy the features of my K-5-IIs and its still fine image quality.
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