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10-25-2009, 10:32 PM   #1
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K-x is king for long exposures and astrophotography!

Greetings everyone. This is my first post to this forum so I thought I'd share something useful. I am an avid astrophotographer and have been using Pentax cameras for many years, namely the LX and 67II. I've also used all of the digitals (except the K-7) but with quite a few limitations due to noise in long exposures.

There have been many examples posted showing the high ISO performance of the K-x, but not much with long exposures. Noise is much different when the sensor is left on for a while and cameras that perform well with high ISO generally don't fair as well over time.

I just got a new K-x in hopes it would be an improvement and I must say it is nothing short of amazing!

These crops are between a K-m (basically the same noise as the K200D and K10D for long exposures) and the K-x scaled to 10M pixels to put them on the same playing field. It was taken with all lights in the room off at f/16, ISO800 to simulate a typical dark astro exposure (very underexposed). There is no NR applied or DFS. Both shots had values stretched the same amount in PS to show the noise.

Since long exposures have much more noise than short ones, plus the fact that these are underexposed, you'll see more than the average noise, but from the world I'm comming from this is absolutely amazing. There is clearly about 2 stops improvement over the old sony sensor Pentax was using. There are details that can be extracted out of the darkest areas that were impossible before.

Based on this I think Pentax finally has a low light/astro camera that clearly beats the competition. I can't wait to hook it up to my 300mm/2.8 or 9.25 schmidt telescope and start imaging the sky. Now if they could just allow the DFS to be turned off for longer than 30s! I guess this will have to be a hack though.

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10-25-2009, 10:38 PM   #2
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No DFS? IIRC the K-m had DFS with any exposure over like 10 seconds or so, although it allows you to disable it completely, but I thought at 30s DFS would've kicked in for K-x. If not, when does it start? So far all Pentax cameras with CMOS do not allow disabling DFS with long exposures, so that's a bummer. I really hope Pentax gives us that option, I don't care how noisy it is since I'll do my own dark frame. Speaking of which, how do you do your DFS at the end of the night with the K-m if you have several exposures of different lengths?

For me, the main reason that the K-x is awesome for long exposures is there is now a custom function option, like the K-7, to allow the remote control's first shutter click to start bulb exposure, and second one to stop it. IIRC this wasn't in the K-m and the only way to do it was to hold the shutter with your finger, either on the remote or the body, and wait.

Noise looks nice, I can't wait to get my white K-x.. damn you Pentax, release it already!
10-25-2009, 11:10 PM   #3
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DFS is mandatory for anything over 30s. Less than that and it will obey the menu selection to turn it off. For most people this is fine but for anyone wanting to stack exposures that are longer than 30s it is a big problem. Since the K-x does so well on long exposures, there is really no reason to force this as there really aren't many hot pixels to speak of.

I usually take anywhere between 15-80 shots a night and then take my dark frames at the end after the thermals have normalized. If there are varying exposure times I take a dark frame for each one so that the times are consistent and then subtract them seperately before stacked. If they are all the same time then it is much easier becasue they can be subtracted and stacked all at once.

I also like the new "B" remote feature. I've wondered long ago why they didn't allow the toggel on/off on this and finally it is here.

The K-x also has an accessory power adapter that slides in place of the "AA" batteries that will be crucial for long nights of exposure time. This will allow me to power from my portable 12V battery (with 6V regulator of course) all night long.

The only thing left to make this the top astro camera is to disable DFS! Why did they have to ruin it.
10-26-2009, 12:47 AM   #4
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QuoteOriginally posted by pti-andy Quote
The only thing left to make this the top astro camera is to disable DFS! Why did they have to ruin it.
You should write to them and let them know. If they wanted to, it should be trivial for them to add that option in firmware.

10-26-2009, 02:42 AM   #5
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QuoteOriginally posted by pti-andy Quote
The K-x also has an accessory power adapter that slides in place of the "AA" batteries that will be crucial for long nights of exposure time. This will allow me to power from my portable 12V battery (with 6V regulator of course) all night long.
Pls keep us updated about using the accessory power adapter that way. It sounds a quite useful setup - eg for heavy use of video away from a power supply.
10-26-2009, 10:49 AM   #6
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Ahh I recognised your avatar, and then saw the subject of the photo and now I know where I've seen the avatar before... Audio circle :P Vifa / Scanspeak soft dome tweeter if im not mistaken?
10-26-2009, 06:13 PM   #7
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QuoteOriginally posted by rawr Quote
Pls keep us updated about using the accessory power adapter that way. It sounds a quite useful setup - eg for heavy use of video away from a power supply.
Will do. I usually use my K200D that has an 6V plug on it and have a regulator that runs from my 12V car electrical system. This also powers my tracking mount and laptop for field use. The K-x however does not have this plug but does have an accessory that is mentioned in the manual to insert into the battery compartment. I expect it will give me the same capabilities as with the K200D.

QuoteOriginally posted by WerTicus Quote
Ahh I recognised your avatar, and then saw the subject of the photo and now I know where I've seen the avatar before... Audio circle :P Vifa / Scanspeak soft dome tweeter if im not mistaken?
Not sure where I got that avatar from. Have you seen it before? If so where? I've had it for many years on my drive and thought it was amusing. It probably came from a site (not in the US). The tweeter is actually an Audax. These are home made speakers. I used this crop because it had high contrast of light and dark.

Edit: I changed my avatar so the above response doesn't apply anymore.

The amazing thing is how you can see the screws and details on the black surface. Keep in mind that this picture was almost completely black before the histogram was streatched. It really shows how much detail is in the shadows of the K-x.

I'll share some field pics once I get out. Anyone else do long exposure shots?

Last edited by pti-andy; 11-13-2009 at 09:29 PM.
11-06-2009, 07:50 AM   #8
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astrophotography

Was just wondering if you had done some more pictures with your Kx? I have been thinking about getting a DSLR but need one that does astrophotography. I tried a couple of CCD cameras made for that purpose but had to return all three types due to problems. I am now back to film for astrophotography. I have a lot of Pentax stuff so am a little unwilling to buy Canon equipment just for night stuff. Anyone tried long exposure stuff with the Kx or other Pentax DSLR's? A lot of my film exposures run from 5 to 45 minutes with ASA from 400 to 1600 for the astro stuff. I have been trying the new B&W film by Kodak with some success but is more grey in tone and requires some digital processing to get really good shots. Any photo processing place can process them which is a plus. The question really comes down to is "are any of the current Pentax DSLR cameras good for astrophotography?" From what I gather from what I have read the answer is "NO". Opinions?

William

11-06-2009, 08:00 AM   #9
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QuoteOriginally posted by WillCarney Quote
Was just wondering if you had done some more pictures with your Kx? I have been thinking about getting a DSLR but need one that does astrophotography. I tried a couple of CCD cameras made for that purpose but had to return all three types due to problems. I am now back to film for astrophotography. I have a lot of Pentax stuff so am a little unwilling to buy Canon equipment just for night stuff. Anyone tried long exposure stuff with the Kx or other Pentax DSLR's? A lot of my film exposures run from 5 to 45 minutes with ASA from 400 to 1600 for the astro stuff. I have been trying the new B&W film by Kodak with some success but is more grey in tone and requires some digital processing to get really good shots. Any photo processing place can process them which is a plus. The question really comes down to is "are any of the current Pentax DSLR cameras good for astrophotography?" From what I gather from what I have read the answer is "NO". Opinions?

William
hmmm.. if "made for astro" cameras don't work for you it may be hard to get any DSLR to do it. Canon made one specifically for this purpose but it is discontinued...
Most normal ccd/cmos cameras (all brands) just are not as good as film for this purpose. At least that is my opinion....
http://www.scopecity.com/detail.cfm?ProductID=5209
http://www.opticstar-ccd.com/Run/Root/Root-Home.asp

Last edited by jeffkrol; 11-06-2009 at 08:08 AM.
11-06-2009, 07:18 PM   #10
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QuoteOriginally posted by WillCarney Quote
Was just wondering if you had done some more pictures with your Kx? I have been thinking about getting a DSLR but need one that does astrophotography. I tried a couple of CCD cameras made for that purpose but had to return all three types due to problems. I am now back to film for astrophotography. I have a lot of Pentax stuff so am a little unwilling to buy Canon equipment just for night stuff. Anyone tried long exposure stuff with the Kx or other Pentax DSLR's? A lot of my film exposures run from 5 to 45 minutes with ASA from 400 to 1600 for the astro stuff. I have been trying the new B&W film by Kodak with some success but is more grey in tone and requires some digital processing to get really good shots. Any photo processing place can process them which is a plus. The question really comes down to is "are any of the current Pentax DSLR cameras good for astrophotography?" From what I gather from what I have read the answer is "NO". Opinions?

William

I have not had a good opportunity yet due to combinations of weather and full moon. I plan on trying this weekend. I will post the results as soon as I get some shots.

I own an Orion Starshoot Pro astro camera but the sensor is so small it is really only good for planets and smaller galaxies. I have done many shots with a K200D and can actually get better results than the cooled astro camera by stacking around 25 1 min exposures. The problem with any of the 10MP Pentax cameras is the noise and random hot pixels that increase the longer the shutter is open. This is why I limit my exposures to less than a minute and just take more of them. The chroma noise shown in my first post shows just how bad it can get in only 30 seconds.

To answer your question... If stacking multiple exposures and processing properly, I can get much better results with the 10MP (K10, K200D, K-m) Pentax DSLR's than any film and I've been doing this for nearly 20 years with a 6x7 and NHG 800. The problem with film is reciprocity failure making your hours of exposure time more limiting has you push on through the night. With the digital I can stack over a hundred exposures and get the real benefit of that precious time in the dark cold night.

That being said, my preliminary tests with the new K-x just blows away the previous generation of 10MP Pentax cameras. There is a minimum of two stops of noise improvement with exposures of 1 minute. It also does not have the extreme chroma noise, hot-pixel, and amplifier glow over time so I believe exposures of up to 5 minutes will be practical. This is hard to achieve with nearly any non-cooled CCD camera today and up till now the CMOS cameras just didn't have the high ISO performance.

I'm very serious when I say that if this camera allowed DFS to be turned off it really would be the best thing for astrophotography for under $2000.

More to follow.
11-11-2009, 01:39 PM   #11
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I'm a newb to both astro-photography and DSLR world and i managed to get this shot using my k-x, deepskystacker, and only 4 exposures (+1 dark frame)

starfield1 on Flickr - Photo Sharing!

shots were taken in manual mode at 30s, iso800, f20, 18mm. I exposed a bit further in adobe raw. stacked in deepskystacker and processed the rest in cs4


i have no idea where in the sky i was shooting or what i actually captured as the 2 green marks but I am pretty sure they are globular clusters. For the camera to capture that detail in 4 30s exposures say to me that i'm not likely to need to take exposures longer then that and ever have to worry about the noise reduction kicking in.

not to mention theres no real way to perfectly time your exposures over 30s without some software aid which the k-x doesn't have and i'd much rather stack then deep deep expose. At least in my limited experience so far the stacking seems to be the smart way to go to get good results.
11-11-2009, 04:40 PM   #12
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Seeing as how you shot that with an 18mm lens, those cannot possibly be globular clusters since they would subtend much less of an angle in the frame. As well, they would never show up as such a saturated green. Not sure what they are, though.

As to stacking, I think you are right on in that the stacking method has many benefits for astrophotography. Lummo Falk has done much study in this area and in fact has developed a program to do multiple stacking to enhance resolution and minimize noise. The program is called PhotoAcute. I have tried it and it works as advertised. Do a search in the forums for both Falk and PhotoAcute and you will get many hits.

I think one of the benefits of the K-x's clean 12800 ISO is that it will allow shorter exposures for astrophotography such that you don't have to worry about as much sensor noise showing up in the frame. I would like to see the combo of K-x 12800ISO and PhotoAcute in action. The results could be spectacular.

Jack
11-11-2009, 07:56 PM   #13
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I've done lots of astrophotography with a K1000, SBIG ST-7E, and a modified Pentax K110D. I live with a lot of light pollution (MAG 3 - 4 sky).

With the SBIG I did exposures of up to 15 minutes when the subject allowed. With the Pentax I seldom exceed 2 minutes due to skyglow and camera noise. There is an advantage to long exposures, 10 * 2 min is not as good as 2 * 10 min. But I live with the shorter exposures of the DSLR since I enjoy the big sensor and one shot color. Due to my location I have been using the internal NR with the DSLR whereas with the SBIG I could start dark frames and go to bed.

Some programs like Images Plus handle stacking frames that have increasing noise due to sensor warm up as the night goes on . The software scales the dark frames as needed. This eliminates the need for taking darks throughout the session to track temperature changes. Images Plus accepts Pentax RAW files. Unfortunately almost no Windows software does the Pentax camera control needed for astrophotography. I use DSLR-Shutter for exposure control, but usually carry the memory card indoors to look at the results!

I agree with jbinpg, the green blob is not any deep space object in the 18mm lens.

I gather the K-x lacks an external 6.5 vdc power jack? How could they drop such a simple and needed feature? Does that accessory require removing the batteries to insert the adaptor? It would seem even a brief loss of power (tripping on a cord in the dark) would abort the session. With my K110D running on external power it will last about 10 minutes on internal batteries, plenty of time for me to discover the power plug fell out and get the external power back on line. I'd say it happens about twice a year!

I'm a die hard Pentax lover but must admit Canon makes better cameras for astro without even trying. The one astro camera they did make (20Da I think it was called) simply had a better red response for nebulas.
11-12-2009, 11:34 AM   #14
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I would love to get into this more. This shot was taken in northern Wisconsin, far away from city light on a moonless night and with my K200d in bulb mode simply propped and hand held on a lake pier. Rather awkward positioning, but the end result was nice

11-12-2009, 11:40 AM - 1 Like   #15
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QuoteOriginally posted by pti-andy Quote

I'll share some field pics once I get out. Anyone else do long exposure shots?
Not really, but it's something I would like to get into. It seems like you really need to get a tracking mount if you want to do any longer glass or longer than ~30 second exposures though, isn't that true? The "barn door" mounts look interesting and it seems that with some care in the design you can make a "manual tracking" version that might be ok for some longer exposures. Any advice on doing something fun on the cheap would be appreciated! I do have some stellar (hah!) long glass but I bet I'd get streaks/elongation pretty damn quick at 300/400mm.

Here's a stack of images, 10 secs each, Sigma 50/1.4 I did the other day as a test... I can shoot it at f/2 and get edge to edge sharpness; my wider lenses are a lot slower so not sure I'd get any more stars in them. E.g. my 15-30 I could shoot at f/4 -- 15mm would let me get longer exposures but it'd be capturing 1/4 of the light of the Sigma so kind of a wash...


Last edited by pingflood; 11-12-2009 at 11:46 AM.
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