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01-18-2016, 07:53 AM   #1
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K3-2 Astrophotography?

Ok, my k3-2 should be here by Friday! I really want to try some Astrophotography with it, but not sure where to start. I have been into astronomy for many years, and understand polar alignment, and tracking, but have no idea at all how all this works with the built in astrotracer! Was thinking of using my scope with the camera mounted on top so I can easily get polar aligned. Probably wouldn't use the mounts tracking, and just rely on the astrotracer. Attached is a picture of my scope. Thanks!


Last edited by Tony3d; 01-31-2016 at 11:48 AM.
01-18-2016, 09:06 AM   #2
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If your telescope's mount is calibrated I'm not sure why you wouldn't use it. You'll need to properly enter the telescope's focal length to have accurate astrotracing using the K3, right?
That does look like it could be fun if you have the sky for it.
01-18-2016, 09:13 AM   #3
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QuoteOriginally posted by Tony3d Quote
Ok, my k3-2 should be here by Friday! I really want to try some Astrophotography with it, but not sure where to start. I have been into astronomy for many years, and understand polar alignment, and tracking, but have no idea at all how all this works with the built in astrotracer! Was thinking of using my scope with the camera mounted on top so I can easily get polar aligned. Probably wouldn't use the mounts tracking, and just rely on the astrotracer. Attached is a picture of my scope. Thanks!
Concerning infos and discussions you should be in good company if you joined the ASTROPHOTOGRAPHY GROUP here in PentaxForums.

If you want to use the Astrotracer stand alone there is no need to go polar aligned because it works on a completely different physical basis.The Astrotracer shifts and rotates the sensor to compensate the relative movement of the stars. So you have to adjust the orientation from time to time before the target gets out of the cameras field of view (because the camera does not "track"). Astrotracer calculates the necessary sensor movement mainly on ist knowledge of actual focal length and inclination/declination of lens axis which is acquired in camera by internal magnetic and acceleration sensors. So you calibrate it each time, point and shoot from a tripod.

Astrotracer stand alone is good for lenses up to 200 mm focal length. It prolongates the possible exposure time by factor 10 (to 15) in comparison to the rule of 500. That is not too much for dim deep sky objects and long lenses (though you can go for Orion Nebula, Andromeda Galaxie, Plejades etc. I even shot M33, M51 and M101 with it @ 200 mm using Picture series and stacking Software DeepSkyStacker). Using the scope as a "lens" together with Astrotracer will not be good because the precision is not sufficient for such a long focal length. Also the aperture of the scope should require long exposure times that the Astrotracer can not deliver.

Astrotracer is great in the field and on trips, for moon- and skyskapes, milkyway etc. But stationary -if you already have a tracking mount- you could use it with the camera piggyback without Astrotracer and have much longer exposure times and precision. And why not attach it to the telescope wit a T2-Adapter and use the mount for moon, sun and deep spce objects?

Last edited by Pete_XL; 01-18-2016 at 09:19 AM.
01-18-2016, 09:20 AM   #4
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Hi, since i am both a Pentaxian and an enthusiast astrophotographer i will try to give some thoughts.

Your mount (Orion Skyview?) and its tracking is surely more than good enough for some piggiback astrophotography up to at least 100mm.
Unfortunately i have no experience with the astrotracer but from what i have read and from my general experience even a poorly aligned mount will deliver much better results than the astrotracer. Its fine if you dont have anything else and a really good thing to get more people into astronomy. But if you have the equipment, use it.

I have used my K3 for some wideangle shots without tracking at all (16mm, 20 seconds) to see how it works for some quick and dirty shots when i dont have the time to use the heavy equipment but gave up on it.
The main problem, at least for me, is the very low sensitivity in all the interesting wavelengths, h-alpha for example. This is a problem for almost all unmodded cameras, so if you want to shot some of the giant nebulae for example you will have to remove your cameras internal filter (which you probably would not do with a brand new K3ii).

Another problem will be noise from long exposures and the resulting sensor heat. The K3 ist good in this regard but if you want to get deeper into astrophotography image noise will become a very big problem very fast.
For example i use a 12MP canon sensor with its filter removed, a CLS-CCD filter added and a watercooled peltier cooling at around -10 Celsius / 15 Fahrenheit at ISO800 and at least sixteen 600 seconds exposures at 200mm f2.8 stacked to get at least decent results.
With 600 second exposures tracking becomes a new problem of course.

Long story short i you want some starfield shots (maybe some bright objects like Orion, Andromeda, Plejades) a K3 mounted on your scope with the mount polar aligned and tracking is perfect. If you want more be prepared to spend some time and money.

01-18-2016, 10:14 AM   #5
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You don't need a Peltier when you shoot at ambient temperatures of -20C up here in the north country in the winter !!!
01-18-2016, 10:31 AM   #6
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I'm not in astrophoto but I have learnt something about temperatures. 20 minutes of video in +34 C shut down my K-3 with temper.... something error. Today I tried to take a small video and my battery died after four minutes. -21 outside. So make sure you have power for your camera.

I can't say how much different video is to long exposure times but both read the sensor all the time.
01-18-2016, 10:47 AM   #7
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QuoteOriginally posted by jbinpg Quote
You don't need a Peltier when you shoot at ambient temperatures of -20C up here in the north country in the winter !!!
Yes, low ambient temperatures definitely help but even at -20C ambient the sensor would be at 10-20C since the sensor heats up to around 35C above ambient, its not that much different from a CPU in this regard.
Every temperature rise of 7 the image noise doubles, and like anemone said, long exposures are like video or even worse.
Note these numbers apply to Canon CMOS sensors but i dont think Pentax/sony sensors behave much different.

When shooting starfields all this is not that much of an issue, but when you try to get the faintest signals from the red channel you want to have the noise in there as low as possible.

Edit: dedicated APSC+ astrophotography cameras (Apogee, FLI, SBIG,...) are 4000-40000$ without filter wheel. One day...

Last edited by Bewatek; 01-18-2016 at 10:57 AM.
01-18-2016, 02:30 PM   #8
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QuoteOriginally posted by Tony3d Quote
Ok, my k3-2 should be here by Friday! I really want to try some Astrophotography with it, but not sure where to start. I have been into astronomy for many years, and understand polar alignment, and tracking, but have no idea at all how all this works with the built in astrotracer! Was thinking of using my scope with the camera mounted on top so I can easily get polar aligned. Probably wouldn't use the mounts tracking, and just rely on the astrotracer. Attached is a picture of my scope. Thanks!
Polar alignment and equatorial mounts are not compatible with the astrotracer. The astrotracer requires that the camera is on a stationary tripod. You either use the astrotracer with the mount motor turned off, or enable the mount's tracking and turn off the astrotracer.

That scope looks like a fairly long focal length. You will probably get better results from using your mount instead of the astrotracer through that telescope.

I recommend 2 ways for you to get started taking photos:
1) The astrotracer works best with wider lenses. Keep things wider than 100mm and the astrotracer is a very portable way to take images of the Milky Way.
2) Use your telescope and mount for images of the moon. That will give you a chance to get started with how to set up and focus. After you get some good moon shots, you might want to advance to other planets or to deep sky photography.

01-18-2016, 04:57 PM   #9
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Wow! Thanks everyone for all the info. I have a lot read. I think I'll start with my manfrotto tripod, and astrotracer. I have the Pentax 18-135mm zoom. I can start with that setup. Should be fun!
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