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10-12-2008, 05:32 PM   #1
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K20D for Astrophotography

I bought a K20D this summer after using my istDL for general photographic use and also for some astrophotography. My problem is that the K20D will not let me turn off noise reduction for long astrophotos. I would take multiple 2 to 5 minute photos and do a dark frame subtraction. The istDL would allow me to turn off the noise reduction, but the K20D will not. Any ideas?

How would I make a suggestion to Pentax about including this in a software upgrade. I love the K20D, but noise reduction makes it nearly useless for astrophotography.

10-12-2008, 06:37 PM   #2
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Maybe maybe shoot in RAW? I don't know for sure, just an idea. You can turn off noise reduction on the K10D, but have to go into the custom settings menu. I'm surprised Pentax would get rid of that setting in the K20D.
10-12-2008, 07:02 PM   #3
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This is s known problem with the Pentax K20D. At this time there is no known fix. Everything has its Achilles heel and astrophotography is the K20Dís. About the only thing I have seen others do who are using it for astrophotography is to take short (1-2 sec sometimes) photos and stack with an astrophotography program.

The K20D can do so many other things well though.

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10-12-2008, 09:40 PM   #4
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Yes, I believe that stacking is the state of the art for astrophotography instead of long exposure in the age of digital. I like the k20d for astrophotography because the live view makes it easier to focus.

10-12-2008, 09:56 PM   #5
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Thanks for the replies. I guess I will have to wait and see if they do a software fix for this "feature". I usually shoot 2 minute exposures, then stack them in software after subtracting a single dark frame (basically what NR does). With NR on, it automatically takes a dark frame and subtracts it each exposure. To get good results, I usually do at least 10 2 minute frames. I love the camera, but if I have to wait an extra 20 minutes waiting for NR, I'm going to just go back to the istDL.

I've attached a photo of Comet Swan from 2006 with the istDL
Attached Images
 
10-13-2008, 05:41 AM   #6
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Yes, it is a bummer that the K20D won't allow noise reduction to be turned off. Some are "getting around" this by putting camera on multiple exposure mode and taking 9 shots on a frame. If you set it to manual exposure and set shutter for 8 seconds or less (if I remember correctly) it won't go into noise reduction if set to auto noise reduction in custom function.
Pentax could have sold me a second K20D if this problem didn't exist. Had to keep the K10D around for stuff like this. Amazingly they cripple their own camera - unintentionally for sure.
There is also a second catch with the K20D and long time exposures. On B the ISO is limited to 1600 or lower.

Nice shot Jay. If you do the 8 sec times 9 you will be 72 sec total. Just have to do that about 20 times instead of 10.

thanks
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10-13-2008, 06:22 AM   #7
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What?
What about setting the NR setting to None? I could have sworn theres a "None, Weak, Weakest, Strong" as well as the "auto" or "on" option.

I have set mine to None (or whatever the minimum/off was called).

Maybe Im confused, but I know what I saw.
10-13-2008, 07:33 AM   #8
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Hey Marlon
I have found that Auto usually never gives me what I want. In this case, the camera will decide what NR is needed. I don't want that. Of course ON is also a bad idea.

The "Off, Weakest, Weak or Strong" option only works with a high sensitivity setting (not defined) and doesn't appear to work in Bulb. I turned it "off" then tried a 10 second exposure at 1600 and came up with the same results, 10 seconds for the exposure, 10 seconds of waiting for the NR.

10-13-2008, 11:20 AM   #9
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That's a cool photo.

I was into telescopes way back in the day. I built an 8.00 Newtonian back in the 7th grade as a science fair project. Optically, it was fantastic. Primary mirror came from Edmund Scientific back when they had some really good ones. I can only imagine what what could have been done with a digital camera and that rig. It would have been so much nice than standing on a ladder...

Was that a telephoto lens or a proper telescope? The question with a telescope is what to do about a clock drive. And a mount. It snowballs really fast.

Restarting THAT hobby is one idea I need to get out of my mind...
10-13-2008, 11:26 AM   #10
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This is my first effort with a camera...

K100D. The main lens is a Sigma APO 500mm. I jacked that up with a crappy (???) Seimar 2X teleconverter that came with a pile of other stuff. I will try again without the teleconverter to see what detail is there.

Back with my old telescope, I could get astounding detail and magnification. Try 5 times the magnification with detail you could almost touch.

I think I am talking myself into another project...

Last edited by jocko_nc; 06-14-2009 at 08:05 PM.
10-13-2008, 04:54 PM   #11
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It is a bummer that the K20D does not allow turning off Noise Reduction. This was discovered and reported as soon as it was shipping to people on this Forum. Pentax is aware of it, but whether they will fix it ???? It is curious that the only Pentax with a CMOS sensor is the only one that forces NR on long exposures.

When taking images with my SBIG astro camera I'd take my own dark frames and subtract them when processing. I actually took 20-30 darks and used them for two or three months. I took bias and flat dark frames every two months also. Only flats had to be taken on the same night and same optics as the light frames.

All this changed when I bought my Pentax K110D. Others may disagree but I'm actually using NR and even a pause to cool down. I find the camera heats up considerably when running 100% duty cycle. In my light polluted location the heat noise soon overwhelms the faint deep space objects. By running 33% duty cycle (2 minute light, 2 minute NR, 2 minute rest) the noise stays in control.

Those using the "Big Two" and who have dark sites to image from can use separate dark frames. Once winter returns I may try separate darks again.
10-13-2008, 06:18 PM   #12
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I don't follow ANY of that but would like to learn more...

Recommend any good reads on how people image through telescopes, technology since the late 70's?
10-13-2008, 07:02 PM   #13
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QuoteOriginally posted by jocko_nc Quote
I don't follow ANY of that but would like to learn more...

Recommend any good reads on how people image through telescopes, technology since the late 70's?
Hi Jocko,

I didn't learn from a book so can't recommend any. I know there are good books out there. Perhaps someone will jump in with a suggestions.

I started out with a K1000 on a used 8 inch SCT 9still my main scope!). Here is an example with a K100D on the same 2000mm telescope. Thirty six frames of 2 minutes each.

http://pages.cthome.net/astroleo/m42-2.jpg

Your 1000mm Moon shot is very good for someone who claims not to understand astrophotography terminology. If you want to get detail in craters on the Moon try when the Moon is 1/2 or less. When the Sun is at an angle the craters cast shadows.

Since faint astro objects are HARD to photograph there are many tricks to improve the image. The different types of frames I mentioned are:

Light frames - the actual photo of the object

Dark frames - as JayLawson mentioned, they are subtracted from the light frames to reduce noise. Rather then use up your time under the stars with NR you can take your own darks at a later time. For my astro camera I'd enough 15 minute darks to last till daybreak and go to bed.

Bias frames - shortest exposure possible, used to remove an offset from the image intensity.

Flat frames - taken of a flat light field to measure what camera sees as white. Flats are divided into the lights to remove dust spots, vignetting, and other flaws. Since you can't always get all the dust off the sensor, flats will fix them.

Flat darks - used to remove noise from the flats.

Many frames of each type are taken. When multiple frames are averaged the noise goes down but the signal stays the same, thus the S/N ratio improves.

For starting out you can just let the camera do NR for you and not worry about the other stuff.
10-13-2008, 09:26 PM   #14
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What software do you used for compiling the various images? I see what you describe but have no idea how would be done.

My last time playing around with telescopes was probably in the early 80's. Obviously, any kind of digital processing that existed back then would been used by the military. I saw the film camera kits but never tried it. Very cumbersome for the unfamiliar. It was various eyepieces and probably a ladder to get up to them.

If one "permanently" mounted a digital body at the top of a large Newtonian, could someone plug in a laptop and control the action from down at the ground? Wow, that would be something.

Is SCT mean the design, Schmitt - Cassegrain?

I got wonderful images from the old Newtonian mirror design. They are just such a PITA. 8 inches in an F10 (I think I had) means you are 80 inches to the focal length. Ouch. I made the tube from old fiberglass water heater cores.

What do you use for a clock drive? Did you build or are they reasonably available?

That moon shot was 1000mm into a .75 crop, 1500mm. Being nearly full, the light was quite bright and the exposure was fairly short. It was early in the night, about 45 degrees to the horizon. I think some distortion and color was due to that.

Yes, I used to love 1/4 moons and such for the crater detail, especially around the poles. My old telescope was so sharp, even at very high magnification.
10-14-2008, 12:43 AM   #15
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QuoteOriginally posted by JayLawson Quote
Hey Marlon
I have found that Auto usually never gives me what I want. In this case, the camera will decide what NR is needed. I don't want that. Of course ON is also a bad idea.

The "Off, Weakest, Weak or Strong" option only works with a high sensitivity setting (not defined) and doesn't appear to work in Bulb. I turned it "off" then tried a 10 second exposure at 1600 and came up with the same results, 10 seconds for the exposure, 10 seconds of waiting for the NR.
Ah, thanks for clearing that up.
Sorry, I misunderstood you.

M
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