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08-14-2015, 09:26 AM   #1
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Astrotracer shows trails, what am I doing wrong?

I tried different combinations, K3 and K-50; 35mm prime, 50 mm prime, 18-135mm; 240 secs, 90 secs, 30 secs. I performed 'precision calibration' on the O-GPS1. I also tested if the sensors are indeed moving - they are (captured a long-distance object on the ground and the resulting images showed movement blur).

Process: I put the cameras in bulb mode, enabled 'Astrotracer' function in the cameras, performed 'precise calibration' in both cameras, set timed exposure, and used both 2 secs timer and cable release (one after another).

What are some things I could be doing wrong? Other things to try to get pin point stars?

08-14-2015, 09:39 AM   #2
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The lenses you used are the Pentax DA series, right?

Can you maybe upload a photo or two, so we can see what it looks like? You can resize it or post a 100% crop, but leave the exif data
08-14-2015, 10:19 AM   #3
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Here's one I took on Wednesday on the K-3....
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08-14-2015, 10:21 AM   #4
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An example image would help. However, in general where were the stars trailing? Along the edges, or across the entire image. Was there more trailing on the longer images?

________________________

It looks like you were probably shooting straight up. It's pretty much the general consensus that shooting with an elevation higher than 45 degrees is going to start to have some trailing problems.




Last edited by interested_observer; 08-14-2015 at 10:27 AM.
08-14-2015, 10:27 AM   #5
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QuoteOriginally posted by interested_observer Quote
An example image would help. However, in general where were the stars trailing? Along the edges, or across the entire image. Was there more trailing on the longer images?

Yup. Just posted one. I should've posted an image in the opening post to begin with. I'll upload some more.
08-14-2015, 10:33 AM   #6
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One more.
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08-14-2015, 10:48 AM - 1 Like   #7
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Very interested in this thread, since I am getting ready to use my recently acquired Astrotracer.
08-14-2015, 10:59 AM - 1 Like   #8
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QuoteOriginally posted by interested_observer Quote
it looks like you were probably shooting straight up. It's pretty much the general consensus that shooting with an elevation higher than 45 degrees is going to start to have some trailing problems.
+1

m

08-14-2015, 11:04 AM   #9
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Hi,

I think that we posted at pretty much the same time - on the first image.

It looks like the second image is much better (in terms of star trailing) than the first one. What was the difference between the two, other than being taken about 13 minutes apart? Was the camera pointed at the same bearing/azimuth? Same elevation (angle up)? Was it pointed above 45 degrees up? Are either of these images cropped?

Also, the tracking approach that Pentax uses in general, works better in some areas than others. Off hand - and I don't remember, it either works better the closer to the equator or the poles. There is a reference to this on one of the Pentax websites/spec sheets.

08-14-2015, 11:22 AM   #10
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QuoteOriginally posted by interested_observer Quote
Hi,

I think that we posted at pretty much the same time - on the first image.

It looks like the second image is much better (in terms of star trailing) than the first one. What was the difference between the two, other than being taken about 13 minutes apart? Was the camera pointed at the same bearing/azimuth? Same elevation (angle up)? Was it pointed above 45 degrees up? Are either of these images cropped?

Also, the tracking approach that Pentax uses in general, works better in some areas than others. Off hand - and I don't remember, it either works better the closer to the equator or the poles. There is a reference to this on one of the Pentax websites/spec sheets.

Shoot, I didn't pay attention to the elevation angle...something to track for next time. The other difference, of course, is part of the sky. The bearings: first image is 69-deg and the second one 4-deg, per the image data on the LCD screen (from true North, I think). Would the detailed EXIF data (extracted from exiftool) show elevation angle?

Neither are cropped.

Thanks for tip about 45-degrees straight-up, I believe I may have been doing that. Lower than 45-deg would probably have showed trees. This was at a Silver Dark Sky site near Cleveland, Ohio - so close to neither the equator nor the poles (even the Earth and Sun consider us 'flyover states'!). Does that mean no matter what I do, stars will trail even with 30 second exposures?
08-14-2015, 11:44 AM   #11
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The stars are going to track somewhat differently depending on the part of the sky you are shooting. Overall, in terms of the approach and process you are using, I don't think that I see anything you are doing "wrong". I have never really applied a 2 second delay, but that is just extra protection in terms of controlling the any vibrations.

I tend to shoot with a wider focal length. Last year, when I acquired the GPS unit was a year of learning. I tried all sorts of things. Based on that, I decided that I really did like the GPS unit, but to help things out, I did go out and get a very fast lens - the Sigma 18-35/f1.8. In some ways it's overkill, also it is a bit more difficult to use since it does not have a hard infinity stop, so focusing does take some time - and luck.

With the K5/K5IIs, I just start out at ISO 1600 and go up from there - with the largest aperture. I have found that at 18mm, 420 seconds (4 minutes) does start to pull star trails around the edges. So, as a note to myself - 240 seconds and kick the ISO up from 1600 to 3200.At first I was shooting straight up at the sky, although I have not done that for a year or so now. I want to try that again. I also want to try shooting with a longer focal length. In a couple of the astro threads, folks have captured some really nice images at 200mm.

I have also been pretty successful at stitching shots together, without using the GPS.
08-14-2015, 11:56 AM   #12
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QuoteOriginally posted by interested_observer Quote
The stars are going to track somewhat differently depending on the part of the sky you are shooting. Overall, in terms of the approach and process you are using, I don't think that I see anything you are doing "wrong". I have never really applied a 2 second delay, but that is just extra protection in terms of controlling the any vibrations.

I tend to shoot with a wider focal length. Last year, when I acquired the GPS unit was a year of learning. I tried all sorts of things. Based on that, I decided that I really did like the GPS unit, but to help things out, I did go out and get a very fast lens - the Sigma 18-35/f1.8. In some ways it's overkill, also it is a bit more difficult to use since it does not have a hard infinity stop, so focusing does take some time - and luck.

With the K5/K5IIs, I just start out at ISO 1600 and go up from there - with the largest aperture. I have found that at 18mm, 420 seconds (4 minutes) does start to pull star trails around the edges. So, as a note to myself - 240 seconds and kick the ISO up from 1600 to 3200.At first I was shooting straight up at the sky, although I have not done that for a year or so now. I want to try that again. I also want to try shooting with a longer focal length. In a couple of the astro threads, folks have captured some really nice images at 200mm.

I have also been pretty successful at stitching shots together, without using the GPS.
Holy crap - those are great images! Interesting technique too, stitching different shots together like that.
08-14-2015, 12:10 PM - 1 Like   #13
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The astro technique is pretty straight forward. Having said that, I always seem to find some small way to screw things up. I get home and while looking at the results, there is always something that I should have done differently, or opportunities that I did not recognize and capitalize on.

My son just moved up to Sedona for a new job, so that means that I now have a new base that I can operate from. It will help reduce the drive and give me more time to shoot, with a completely different landscape and it's much darker there.

08-14-2015, 12:21 PM   #14
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I don't have an Astrotracer, but every time I've tried the DA35 2.4 for stars, my results have looked like yours. I hate this lens for stars. The always look soft to me, not sharp. Same with the 18-135. I use an SMC M28mm 2.8, Fa50 1.4 and Rokinin 16mm with great results.
08-14-2015, 12:43 PM   #15
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For those hard to do angles, build yourself an Astrotracer. These tangential "barn door" types are good for several minutes tracking. This one I made is for wide angle lenses and you rotate it on the marks every 15 seconds max. More frequently if you want but with a WA lenses it does fine.

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