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08-25-2016, 01:15 PM   #1
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Attempting to Master the Astrotracer Functionality

I've been experimenting with the astrotracer function and am not achieving the expected results. As far as I know I've done all that is needed - using the GPS and the calibration function. The camera indicates the calibration is OK. Here's a crop of an example shot taken in my yard. As shown there is a star trail and the foreground is blurred (my neighbor's roof) as expected. I'm using a sturdy tripod setup and an electronic timer to control the exposure. Any suggestions for getting better results are appreciated.



08-25-2016, 01:35 PM   #2
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The roof shouldn't be blurred as far as I figure how things are supposed to work. Leaves on trees yes, not roofs - it's way too close, you should avoid nearby objects. I wasted a whole battery charge in my K-3 II until I figured how to set it up properly and got really clear images of the Milky Way shot from my backyard. Saw better ones than mine, though, but for the first time, I consider myself lucky and happy with the results. Tried all kind of arangements starting with ISO 200 and 120 sec (F2.8-F11) and gradually getting pretty close to what I want at 30 sec, F2.8 and ISO1600... Found images above ISO 1600 to be noisy and played further increasing exposure time to 40 sec and reducing sensitivity. Later figured out that the Moon was not far enough behind the camera and made mess so I gave up until better conditions....
08-25-2016, 01:44 PM   #3
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QuoteOriginally posted by PhilRich Quote
As shown there is a star trail
Since the star trail occurs with all the stars, I'd doubt it is a lens distortion issue.

I note you have a 300 second exposure with f5.6, ISO 100. I'd try to open the lens up a little more to let a bit more light in. Take advantage of that f2.8. I've read that some take an exposure only half to three quarters the theoretical maximum for best results. Try increasing your ISO to 1600 as well. You might want to stack a few images as well.

That said, some folks have reported that the astrotracer function simply does not work well from certain areas when pointed in certain directions. So you can change locations to try and rule that out.

Good luck!

Last edited by rgknief60; 08-25-2016 at 01:57 PM.
08-25-2016, 02:08 PM   #4
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If that's a 5-minute exposure, visible star trails are to be expected. But I'd like to know the full exif, as that will help us guide you


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08-25-2016, 02:19 PM   #5
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I had to give up on the Astro Tracer function and go to a tracking mount. Some of the lava rock here on the Big Island, and the island really is the world's largest chunk of lava, has very high iron content. Some pieces and cross sections have so much iron content that it looks red like sandstone from the southwest US. Out near recent new lava flows I was unable to get a calibration regardless of number of attempts. At my residence I can periodically get a calibration reading, depending where I am physically at in my yard. Joe Virgil at Pentax confirmed that some locations will have difficulty getting proper compass readings, in conjunction with the onboard GPS, to calibrate properly.

And FWIW, a well set up tracking mount does work in conjunction with pixel shift, even with 30 second exposures. The error is so small that no noticeable artifacts are induced except for occasional aliasing that is visible on some brighter stars at 150-200% magnification. As you can't use pixel shift with AstroTracer, I now prefer the iOptron mount.

My bigger issue has been the white dot problem with long exposures. The dark frame solution works against certain types of night sky work. There seems to be no immediate cure as it is a design function/flaw of the sensor and while all sensors exhibit this issue to some extent, without dark frame subtraction, my long exposure images are unusable.

Last edited by CDW; 08-25-2016 at 02:28 PM.
08-25-2016, 02:45 PM   #6
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QuoteOriginally posted by PhilRich Quote
I'm using a sturdy tripod setup and an electronic timer to control the exposure.
I don't think I understand your "using an electronic timer to control"? In Bulb-Astrotracer-mode, Astrotracer is your timer. Also, which lens have you been using? If it's a manual lens and the focal length has been entered incorrectly, you will typically get star trails as we see them here.
08-25-2016, 04:41 PM   #7
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It seems sort of odd that the roof would be blurred. A remote (wired or not wired) that eliminates contact with the camera is a necessity if you are possibly not using one, unless you are using the delayed timer (drive mode) in Manual for 30 second and under exposures. I am assuming you are using Bulb mode. Your shot does not look that bad with the exception of the blur degrading it. Like others have mentioned, testing with possibly a shorter exposure time (for example 30-120 seconds), an ISO that does not produce too much noise (100-800 if possible), and an aperture that will give you generous light according to what you have available is a way to see what produces a satisfactory image for you. The light can vary depending on where you are (ex. proximity to city lights) and the moonlight presence, so trying a variation of F Stop, Shutter Speed, and ISO settings is going to show you what works best for you and your equipment. Providing proper focus is also a necessity. Good luck.

Last edited by C_Jones; 08-25-2016 at 04:56 PM.
08-25-2016, 05:28 PM   #8
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It is normal for stationary terrestrial objects to be blurred in AstroTracer shots. The sensor is tracking the night sky, which is relatively sharp in the poster's image.

08-25-2016, 09:29 PM - 1 Like   #9
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Expecting perfect dots with a 5 minute exposure is asking too much. When you consider the rotation of the galaxies in the sky, you're inherently attempting to translate the movement of a spherical view onto a planar surface. The geometric differences between sphere and plane become far more obvious with extreme wide angles, which is why many users are reporting astrotracer failure using ultrawide 14mm lenses. It's not the astrotracer, it's the geometric translation of the actual world onto the flat sensor... no amount of sensor movement can correct for that for such long exposures.

Here's my proof - I shot this with a K-1 using 1 minute exposures on repeat.

Instagram

Watch the stars exclusively at the left end of the frame. they're not trailing in the conventional usage of the world, but they're moving INTO the frame faster than they're moving when they near the center of the frame. That's the nature of spherical rotation versus simple planar linear transformation. And that's at 24mm. The effect is far more pronounced at 14mm.

The astrotracer gives Pentax abilities that no other camera manufacturer can offer without significant 3rd party equipment. Just like you wouldn't crank the clarity or sharpen sliders up all the way in post, extending the astrotracer exposure time to the max is also not responsible practice. Any other camera manufacturer shooting 1 min exposures at 24mm would have legit trailing all across that timelapse. Pentax astrotracer gives me cleaner dots at 1 min than other manufacturers get at 20 seconds... plus the extra 1.25 stops.
08-26-2016, 12:58 AM   #10
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QuoteOriginally posted by CDW Quote
It is normal for stationary terrestrial objects to be blurred in AstroTracer shots. The sensor is tracking the night sky, which is relatively sharp in the poster's image.
At five minutes or three minutes, yes, not at 20-30 seconds.
08-26-2016, 02:33 AM   #11
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QuoteOriginally posted by stein Quote
At five minutes or three minutes, yes, not at 20-30 seconds.
And this was 5 minutes.

As already stated, going for maximum allowed time is probably a bit optimistic. It could work if all the sensors reports perfect values, but more often than not they donít.

I have only just started to experiment with the compass on the K-1, and so far Iím not getting nearly as good results as I am able to get with the ogps-1.
08-26-2016, 06:27 AM   #12
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Don't know if that matters or not, I use the "Space Map Pro" app on my windowsphone (Lumia 640) and it's a great help to easily figure out in an instant where is what on the sky and in which direction to turn my camera if I want to shoot a particular part of the sky. The only "issue" I have is that my K-3 II drains the battery really quickly when working with long exposures. D-BG5 (replica) is already on it's way... Have a load of GP "Recyko" AA batteries and that should solve it.
08-26-2016, 12:14 PM   #13
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Just for fun, I was playing the other night with mine. I did a before and after type test. Took a 15 second shot and a 30 second shot with Astro Tracer off, just to get a base line of what to expect for trails. I used my DA-70 Ltd lens for the test. As expected, small trails at 15 seconds, and longer at 30 seconds. With the Astro on, I got upwards of 60 seconds with stars just starting to show a bit of movement (and only because I was looking for it) At 90 seconds, I was getting about the same as the 15 seconds without the Astro turned on. I was impressed to see the difference. For me, the hardest part was getting good focus, but once I got it, all was good.
08-26-2016, 03:39 PM   #14
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QuoteOriginally posted by Adam Quote
If that's a 5-minute exposure, visible star trails are to be expected. But I'd like to know the full exif, as that will help us guide you
I'm not sure on how to show the exif file here or what specific info you are looking for.

I've been away for a while so haven't responded to comments until now. I find some of the comments confusing. My impression is that the astrotrack feature should provide a star image as a point not a "track". I've used shorter (say a minute or two) and always get the track. So I think that I'm doing something wrong.

As regards the electronic timer comment - it simply controls the time of the exposure when in bulb mode. If you want two minutes, dial in two minutes and that's what you get without having to push the exposure control on the camera.

It seems to me that the purpose of the astrotracer feature is that you do not have to crank the ISO up to very high levels and use a wide open aperture. I used f5.6 to get best corner to corner resolution for the picture posted.

Would someone please post a picture in this thread of a properly executed astrotracer picture. One that has several minute exposure. That may help me to adjust my expectations. Thanks.
08-26-2016, 06:06 PM - 1 Like   #15
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QuoteOriginally posted by PhilRich Quote
Would someone please post a picture in this thread of a properly executed astrotracer picture. One that has several minute exposure. That may help me to adjust my expectations. Thanks.
Who needs several minutes?



No extreme ISO, no exorbitant long exposure, not even using the widest aperture on the lens. 24mm, ISO 1600, f/2.2, 60s. My post above has a timelapse of 130 of these exposures in a row.

---------- Post added 08-26-16 at 08:52 PM ----------

More? OK.



24mm, ISO 1250, f/2.2, 60s. Astrotracer works. Both in the portrait and landscape camera orientation (I've heard that complaint in similar threads). Without it, both of these shots would be trailing noticeably even with one third the exposure time.
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