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07-21-2014, 01:53 AM   #1
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Hello & Long exposure K-3 noise profiling

Hi people,
I'm new to this forum, let me introduce myself and wish all you very clear and astonishing shots with your Pentaxs!

The reason to enter the forum is that I am thinking in purchasing a new camera (I got MANY years ago one K110) because the K110 is tooooo noisy for doing nocturne pictures. I am an amateur astronomer, and have been doing astrophotography for long years. My K110 can not go longer than 60 or 90 seconds without showing the terrible thermal noise that plague its CCD sensor. Recently I took a shot where I could even see the top left CCD frame glowing in red (mainly) because of the small heat generated by the output electronics placed in that area of the sensor!

My question is: some user/owner of a new K-3 could make a set of shots with the optics of the camera closed with a cup ('DARKS') exposing in the range of 180-300 seconds long?
F number and optocs are irrelevant. ISO is important in the test trial. Can a K-3 shot beyond ISO1600 and longer than 30 seconds? A set of trials with ISO 800, 1600 and 3200 would be great. Ambient temperature in the range of 15-30C would also be OK.

The K-3 will not be mainly used for taking pictures through the telescope, but for nocturnal and light painting landscapes, on tripod and nights with temperatures spanning -8 to 35C degrees.

I attach one picture with my K110 showing the high noise that this camera presents, otherwise a VERY good camera (perfect for the price I paid) for regular use, full of performances only found in superior brands or models.

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07-21-2014, 01:46 PM   #2
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Hi and welcome!

There are several astrophotographers on here, so I'm sure you'll find someone who can help you out. It might be a good idea to ask over at this thread: https://www.pentaxforums.com/forums/172-pentax-k-3/244417-k-3-astrophotography.html

Or start a new thread in the K-3 section
07-22-2014, 02:29 AM   #3
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Welcome here, I'm sure one of the night sky guys will be along in a minute to help you with you question.
07-24-2014, 12:03 PM   #4
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Hi, Max. I have just completed a run of darks for various ISOs as you requested. There were some surprising results for me. I cannot post the full raw files here due to size so I will just convert to jpeg and post. If you want the full raws, I will put them on my dropbox and you can download them from there.

Jack

07-24-2014, 12:25 PM   #5
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K3 noise profile - ISO1600

OK, Max. Here are the ISO1600 darks for 3 minute and 5 minute exposures. Viewfinder blind in place. This can be viewed as a baseline for astro work given the minimal thermal noise. 3 minute on top.

Jack
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07-24-2014, 12:27 PM   #6
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K3 noise profile - ISO3200

And the same for ISO3200. 3 minute exposure on top.

Jack
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07-24-2014, 12:33 PM   #7
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K3 noise profile - ISO6400

And a couple of the ISO6400 darks. Since this ISO was the basis of your query, I did four exposures at this ISO, two with no viewfinder blind and two with the blind. I was shocked to see the difference the blind makes. Here are the 3 minute exposures. No viewfinder blind on top (obviously).

Jack
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07-24-2014, 12:37 PM   #8
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K# noise profile - ISO6400 again

And here are the ISO6400 5 minute darks. No viewfinder blind on top again.

Jack

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07-24-2014, 12:40 PM   #9
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K3 noise profile - ISO12800

And for a lark, I did an ISO12800 pair as well with the viewfinder blind in place. 3 minutes on top. The thermal noise is very well controlled in the K-3 and quite linear. But a viewfinder blind is essential for longer exposures.

Jack

---------- Post added 07-24-14 at 12:47 PM ----------

Forgot to mention that all exposures were made at room temperature. Only the base curve was applied in post to make the blacks black. No other adjustments made.

Jack
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07-25-2014, 03:49 AM   #10
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Original Poster
Hello Jack,
many thanks for your very good review of the K3 dark performance! I am supposing that your shots will be of high interest for us astrophotographers/nocturnals aficionados.
Those shots has been decisive, I think that we can say with no doubt that the K3 is a good camera for night working, join that with the ability to work below 0 and the needing to purchase a one-shot color astrocamera may be discussed.

It is very important the discovering of the effect the blind cup for the viewfinder does in long exposures, may be that some good long exposures would had come ruined because of light leaking through the viewer. It is something to take into account.

I would like to have the raws of the darks. I do not promise, but I would try to make an statistical analysis of the noise profile.
What was camera's the approximate temperature? Did you find noise increasing from shot to shot due to sensor heating?
Please excuse me if I do too many questions, when I got my K3 I will throw a full test trials on it!

Best regards from Spain.
Max.
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