[vinikrish]

Hello,

I am new to the Pentax system and astro photography with bigger focal lengths. Of course the main feature that made me switch to Pentax is the astrotracer feature.
My question is, how do people manage to take multiple hours of images since astrotracer does not actually "track" the stars? Do we have to reposition the stars/ constellation to the middle of the frame after each shot? or people do any other mechanism to automate the process? I would be very interested to hear different options...

Thanks in advance!
Vineeth

[MossyRocks]

My question is, how do people manage to take multiple hours of images since astrotracer does not actually "track" the stars? Do we have to reposition the stars/ constellation to the middle of the frame after each shot? or people do any other mechanism to automate the process? I would be very interested to hear different options...

I frequently use astrotracer and once I get things calibrated and focused I use an intervolometer to take several shots with the object moving across the frame from shot to shot. I will usually take 6-8 shots like this at 400mm before repositioning the camera and then begin the process anew. This method actually has one benefit as it basically auto dithers the image so that hot or cold pixels get erased during the stacking process and the dither also in theory allows one to make use of the ability to upscale and do a super resolution image (drizzle is the astrophotography term for it). The downside is that because not all portions of the final image have the same number of exposures noise will generally increase as you go towards the edge of the frame.

Also when I say frequent user of this feature I do use it a lot and take images with total exposure times measured in hours. Some examples of what I have done using that technique and using my 400mm lens. These are the actual framing one gets at 400mm with an APS-C format camera:

About 90 minutes of the Pleiades (M45, the Seven Sisters, or if in Japan Subaru):


2 hours 45 minutes of the Andromeda Galaxy (M31):


Almost 9 hours of the Great Orion Nebula and Running Man (M42), I reprocessed this this week so I actually have an even better image that I need to post at some point:

[AstroDave]

Well, astrotracer sort of follows the stars - by moving the sensor to counteract the apparent motion of the sky due to the earth's rotation. Since the sensor can move only so far, that limits how long an exposure can be. If your celestial object stays in the overall camera frame for longer than one exposure, you can take several in a row, but at some point, yes, you will have to adjust the aim of the camera.

Others here should be able to tell you more about how long you can keep this up. I hope MossyRocks chimes in! He works wonders with this stuff.

If you are serious about hour-long exposures, you will need a polar tracking mount. Even then, you will probably want to take numerous shorter exposures (~ a minute) and stack them in software.

ps welcome to the Forum. You will find lots of helpful folks here.

Well - MossyRocks beat me to it!!!!!

[Paul the Sunman]

Welcome to the forum. Please post some of your images when you get a chance.

---------- Post added 11-12-21 at 07:57 AM ----------

About 90 minutes of the Pleiades (M45, the Seven Sisters, or if in Japan Subaru):


2 hours 45 minutes of the Andromeda Galaxy (M31):


Almost 9 hours of the Great Orion Nebula and Running Man (M42), I reprocessed this this week so I actually have an even better image that I need to post at some point:

Impressive work MossyRocks!

[Bob 256]

Really, really good shots MossyRocks - now we know what Rocks in your user name refers to.

The OP's other option, though not an AstroTracer application, is to use a guided mount. With a mount, exposure time extends long beyond what AstroTracer can do and you can keep your main subject centered, but there are drawbacks to a mount in terms of setup, alignment, tracking, and transport which AstroTracer has the edge on.

[MossyRocks]

With a mount, exposure time extends long beyond what AstroTracer can do and you can keep your main subject centered, but there are drawbacks to a mount in terms of setup, alignment, tracking, and transport which AstroTracer has the edge on.

As someone who use astrotracer and also owns a small equatorial and will run both when out there are advantages to both. Equatorials have weight capacities and for good tracking you want to be at no more than 50% to about 66% of their mas capacity and this is not a limitation that astrotracer has. Astrotracer, the one that uses the GPS, electronic compass, and level sensors, is actually rather finicky and takes some getting use to but it can work very well once one starts to master it and knows an area and what to watch out for. Depending on the focal length the polar alignment of an equatorial doesn't have to be terribly close and I think with my 12mm lens I so long as I have polaris in the polar scope it would track just fine. However astrotracer is really best when one gets into normal to telephoto fields of view since the difference in the rotational component of movement from one edge/corner to another isn't very great but with ultrawide lenses one gets greater tracking errors as you move farther from the center of the frame. When using an equatorial that isn't a problem as the tracker keeps the same field of view on the sensor. For what I run on my little equatorial typically getting a good polar alignment doesn't take much longer than getting a good astrotracer calibration (rarely do I get it on the first try) so that is a wash. There is a greater setup time for the equatorial but we are talking only several minutes. When I consider transport the tripod I use the camera with astrotracer on is actually bigger and heavier than the one I stick my little equatorial on and the astrotracer tripod is actually bigger, heavier and more stable than the tripods that come with even a big equatorial. The tripod I use for my equatorial is an old Manfrotto 3058 tripod with a 3057 head. but this is my big ultra heavy duty tripod I use with the big glass and astrotracer. Granted that isn't a fair comparison as most wouldn't have that big wooden tripod but for me the transport ends up the same where as others would run astrotracer off of a smaller aluminum tripod so they would enjoy better mobility.

I am at the stage where getting a really big equatorial is in the general plan with all sorts of extras (autoguider and everything to make that work) so that means even more setup and gear. So my suggestion for others is that astrotracer is a good entry point and a huge boost for not a lot of money for someone starting out with astrophotography. This was one of the reasons why I stuck with Pentax when making the jump to digital.

[Mikesul]

Those are very impressive shots, MossyRocks. The Orion nebula was almost scary it was so beautiful.

[bwgv001]

@MossyRocks; how do you make sure you are properly focused? that to me is so far the biggest challenge, I tried a 300/F4 but the focuspoint is so hard to get; the slighest turn gets the lens out of focus. Any advise?

[MossyRocks]

@MossyRocks; how do you make sure you are properly focused? that to me is so far the biggest challenge, I tried a 300/F4 but the focuspoint is so hard to get; the slighest turn gets the lens out of focus. Any advise?

For my long glass I have bahtinov masks for them. So there I have one that fits inside the slide out hood for my 300/4 and for my 400/2.8. You can buy ones that work reasonably well for shorter glass like these these I bought and have used them on a lens as short as my 50mm ones. At 50mm you basically get 7 dots at 10x magnified live view.

Without using a focusing aide your best bet is manual focus in magnified live view with focus peaking off so you can minimize the star size. I mostly run old lenses but my 300/4 is the Sigma 300/4 APO tele macro and has a very sensitive focus near infinity. It took lots of practice before I mastered moving the focus on it to get things right.

[MossyRocks]

The Orion nebula was almost scary it was so beautiful.

If you liked that one when I say I went back and reprocessed that stack to get more out of it this is what I manged:


Again all the shots that were stacked for that image were taken with astrotracer on my K-3.

[DamienW]

I have a K-1ii. I have a Star Adventurer mount. I have never used the Astrotracer, preferring the mount. Friend of mine also has the K-1ii, but no motorised EQ mount. There has been colourful language pretty much every time we've gone out to do astro together.

If I'm shooting a longer focal length (and this is usually NOT with my K-1, but actually with a micro four-thirds camera), I find I rarely have to make adjustments to the camera position...it just follows the rotation so nicely. If I was using my K-1 with astrotracking, I would have to adjust it quite frequently.

K-3iii GPS-less tracking. Well...this is very exciting indeed. For your type of shooting though, how much will you get out of it? If you're taking a series of shots over even a fairly short period with a long focal length, can you even keep the subject in frame for the series?



---------- Post added 12-10-21 at 08:11 PM ----------

If you liked that one when I say I went back and reprocessed that stack to get more out of it this is what I manged:


Again all the shots that were stacked for that image were taken with astrotracer on my K-3.

That is a very nice image. I think just go with whatever MossyRocks says.

[shyrsio]

MossyRocks those are some astonishing images you got there!

[MossyRocks]

MossyRocks those are some astonishing images you got there!

Producing good images isn't all about taking them but also learning how to process them. It takes lots of practice doing both and it is really rough when one starts out as you will see images from others that are great and be let down by your own. I was like this but kept at it and eventually started producing some reasonably good ones. A big help were those over in the astrophotography group so if that is your thing go join it. We may be odd in that we go stand out in the middle of nowhere at night when ever we can but will help others out so ask questions early and often. My other advise is to start off easy and simple both in editing (levels and curves) and objects (pick the bright ones that are easy to find). As far as a good inexpensive starter lens get one of the Pentax A, M, K, or M42 200mm F/4 lenses and run it at F/5.6. They are good lenses and most of the time I can find the locally for between $60 and $100.

[PixL8]

I have no idea on this but I am very interested in the answers... Thanks for asking this question.