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06-24-2016, 11:06 AM   #1
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Another user getting star trails with the Astrotracer

This seems to be a common problem. I suspect it's something I'm doing wrong and I'd appreciate any tips. The weather is supposed to be good next week and I'm hoping to get some good milky way shots.

I have a K-3II, which is what I'm hoping to use and I also have a K-50 and an O-GPS which I bought some time ago but haven't really used.

This is what I did with both cameras.
1. Turned on the GPS, and waited until it acquired a position.
2. Did a calibration.
3. Turned on the Astrotracer
4. Did a precise calibration.
5. Took the images.

All Images are with the M28 F2.8 (and yes the focal length was correctly set in camera). I started after sunset and worked for an hour or two so the ISO varies some. I was just trying to get star images without blowing out the background, not trying to get great shots.
These are 100% crops. The star is Deneb (in Cygnus).
According to the astrotracer I should have been able to go as high as a 5 minute exposure.

Here are the results from last nights test.

1. A 30 second control image taken with the K-3II without using the Astrotracer.
2. A 30 second image from the K-3II with the astrotracer. This image was so poor I didn't try anything longer with the K-3II.
3. A 30 second image from the K-50 with the astrotracer (O-GPS), A little egg shaped but not bad.
4. A 120 second image from the K-50 with the astrotracer (O-GPS). Disappointing...
5. A 60 second image from the K-50 with the astrotracer (O-GPS). More egg shaped. (sorry these are out of order but I couldn't change it once uploaded)

I've seen some really stunning results from others so I'd appreciate any help

Attached Images
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PENTAX K-3 II  Photo 
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PENTAX K-3 II  Photo 
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PENTAX K-50  Photo 
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PENTAX K-50  Photo 
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06-24-2016, 11:19 AM - 1 Like   #2
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QuoteOriginally posted by JimS_256 Quote
According to the astrotracer I should have been able to go as high as a 5 minute exposure.
Roughly 30 to 90 seconds is what I would realistically expect, though it all depends on the focal length, where you are, and how well you calibrated.

It looks like your K-3 II isn't calibrated properly, so just do it a few more times and your pics should start looking better. It's a good idea to turn the camera 180 degrees in both directions along each axis, instead of doing complete revolution in a single motion. This allows you to hold the camera more steadily.

The K-50 looks like it's close to where it should be. The 30s and 60s shots look fine. By calibrating some more you might be able to make them look even better.

Good luck!

Adam
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06-24-2016, 11:43 AM - 1 Like   #3
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I've gotten pretty good results with the k3ii. Sometimes I need to do a second precise calibration if I get trails, but the main factor so far has been how well I manage to steady the tripod. It's not just the tripod's quality or using a cable release / timer, but also making sure it doesn't sink in the ground ever so slightly -- let is settle for a few minutes.
Another thing which may only be I myth I created: I try to keep my phone in airplane mode and far away from the camera in order to avoid magnetic changes, but I have no proof that it actually affects anything

More (most?) importantly, depending on the cardinal direction to which you point the camera, the stars' motion is not parallel so the camera will not be able to compensate for all the same. Straight north and they all rotate, so what's in the center barely moves, the outer ones do a circle, and if you get anything more to the east or west it will likely be linear. With a wider lens it's more likely this will be the case. Here's an example: Understanding Astronomy: Motion of the Stars
06-24-2016, 12:48 PM - 1 Like   #4
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QuoteOriginally posted by aaacb Quote
I try to keep my phone in airplane mode and far away from the camera in order to avoid magnetic changes, but I have no proof that it actually affects anything
Perhaps not, but local magnetic disturbances DO influence the accuracy of the compass calibration and if disturbances are strong, they may corrupt the whole setup. So, further to Adam's suggestions above, I would recommend the OP to:


1. Try moving around to see if changes in position have any effect on results.
2. Try out the astrotracer at more stars in different directions (azimuth)


Further:
3. Try out the astrotracer on stars of different heights above the horizon (altitude). I can see that images are shot from a position at 48 degrees latitude, meaning that Deneb must have been fairly high in the sky (>45 degrees?). The compass heading accuracy degrades as altitude increases and although 45 degrees shouldn't be an issue for Astrotracer, I would also try stars or planets nearer to the celestial equator. Currently, Jupiter, Mars and Saturn could serve as such "test objects".


My own experiences with the Astrotracer on a K-5 and K-3 tells me that you can achieve - and are entitled to expect - far better results, so don't give up!

06-24-2016, 05:18 PM   #5
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QuoteOriginally posted by Adam Quote

It looks like your K-3 II isn't calibrated properly, so just do it a few more times and your pics should start looking better. It's a good idea to turn the camera 180 degrees in both directions along each axis, instead of doing complete revolution in a single motion. This allows you to hold the camera more steadily.

Good luck!
It's interesting looking at the K-3II tracking image (photo#2). It appears to be tracking in the correct direction but at about half the speed necessary to eliminate the star trail. Like it was tracking for a 14mm lens instead of 28mm (and yes, I double checked that I entered the correct value)...

For calibration I used the technique shown in this pentax video.

I will try doing a second (or more) precise calibration to see if that helps.

QuoteOriginally posted by aaacb Quote
Another thing which may only be I myth I created: I try to keep my phone in airplane mode and far away from the camera in order to avoid magnetic changes, but I have no proof that it actually affects anything
That's easy enough to do, I'll give it a try. Thanks for the suggestion.

QuoteOriginally posted by Stone G. Quote
Perhaps not, but local magnetic disturbances DO influence the accuracy of the compass calibration and if disturbances are strong, they may corrupt the whole setup. So, further to Adam's suggestions above, I would recommend the OP to:


1. Try moving around to see if changes in position have any effect on results.
2. Try out the astrotracer at more stars in different directions (azimuth)


Further:
3. Try out the astrotracer on stars of different heights above the horizon (altitude). I can see that images are shot from a position at 48 degrees latitude, meaning that Deneb must have been fairly high in the sky (>45 degrees?). The compass heading accuracy degrades as altitude increases and although 45 degrees shouldn't be an issue for Astrotracer, I would also try stars or planets nearer to the celestial equator. Currently, Jupiter, Mars and Saturn could serve as such "test objects".
I'll try some different locations and different stars to see if I get any better results.

I checked, Deneb was about 37 deg above the horizon when I started and at about 43 deg. when I finished. The time stamp on the image Standard time so it's off local (daylight) time by an hour (really 10PM instead of 9)

QuoteOriginally posted by Stone G. Quote
My own experiences with the Astrotracer on a K-5 and K-3 tells me that you can achieve - and are entitled to expect - far better results, so don't give up!
Thanks,that's good to know. I realize that the times listed by the astrotracer are optimistic and should be (at least) halved but (using a 28mm lens) I was expecting my 2 minute image to look more like the 30 second one (and the 30 second one to not have any oval/egg shape).
06-24-2016, 05:20 PM   #6
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The direction you point your camera will affect the time you can work too. There is a thread.. I can't find at the moment.
06-24-2016, 06:24 PM   #7
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QuoteOriginally posted by mattt Quote
The direction you point your camera will affect the time you can work too. There is a thread.. I can't find at the moment.
Here are some Ricoh charts on that: Specifications | GPS UNIT O-GPS1 | RICOH IMAGING

My sample images are well under the max.
06-24-2016, 07:13 PM - 1 Like   #8
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A few more questions...
  • Did you calibrate near anything that is large and metal - like a car? Anything metal will introduce a bias/error into the compass. You need to move about 10 to 15 feet away for the calibration.
  • I try to do the precise calibration rotating the camera body 180 degrees in each direction around the axis. Even with a successful calibration, I have gone back and done it a second time, just to make sure.
  • Where in the frame did you chip the examples from? Center? or along the edges/corners of the frame? It makes a difference. The center of the frame, the stars should always be in a point. Long term exposures 90 to 300 seconds, the stars along the edge start to trail, since the sensor is not able to track perfectly in 3 dimensions. Over time an error component grows - which results in trailing along the edges.
  • Just for a point of reference, using a 18mm lens, I get good point stars at 60 second exposures (which is about 6 times longer that with out the GPS unit).



06-24-2016, 10:01 PM   #9
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Same procedure with the built-in GPS

06-25-2016, 09:38 AM   #10
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Thanks everyone for your comments!

QuoteOriginally posted by interested_observer Quote
A few more questions...
  • Did you calibrate near anything that is large and metal - like a car? Anything metal will introduce a bias/error into the compass. You need to move about 10 to 15 feet away for the calibration.
  • I try to do the precise calibration rotating the camera body 180 degrees in each direction around the axis. Even with a successful calibration, I have gone back and done it a second time, just to make sure.
  • Where in the frame did you chip the examples from? Center? or along the edges/corners of the frame? It makes a difference. The center of the frame, the stars should always be in a point. Long term exposures 90 to 300 seconds, the stars along the edge start to trail, since the sensor is not able to track perfectly in 3 dimensions. Over time an error component grows - which results in trailing along the edges.
  • Just for a point of reference, using a 18mm lens, I get good point stars at 60 second exposures (which is about 6 times longer that with out the GPS unit).

No, nothing large and metallic was nearby.

That sounds like the calibration technique I've been using. I tried to copy the procedure shown in the pentax video (see my link in post #5 or Not a Number's link above). If anyone has any suggestions on improving the technique shown in the video, I'd love to hear it.

The crops are all from the central portion of the frame. I was aware that the edges of a wide angle lens could be problematic.

Thanks for the reference point. While Pentax seems to promise much better in their information and sample images, I would be fine with that.
07-05-2016, 02:55 AM   #11
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is it possible you were shooting over the Bermuda Triangle??
I've heard things...
07-11-2016, 03:20 PM - 1 Like   #12
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QuoteOriginally posted by mikeSF Quote
is it possible you were shooting over the Bermuda Triangle??
I've heard things...
LOL. Nope I can safely say that isn't the problem.

I've been out one other time and gotten similar results, maybe slightly better but not much.

This time:
I made sure that I wasn't near anything magnetic, including removing my cell phone and a large metal belt buckle (I really thought the belt buckle might be this issue).
Tried shooting stars at different declinations and altitudes.
Did the precise calibration every time I went to a different part of the sky and at least twice before starting.

Nothing made much difference.
07-11-2016, 04:56 PM - 1 Like   #13
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It's trial and error to find a combination that works well with the thing, I have had much better success at the long end and get clean exposures @ 300mm of up to 60 seconds whereas with the 10mm it seems to vary a lot.
A few things that have caused problems for me were the ground (how stable was it), were there any vibrations, even a little breeze can mess things up. Try the digital zooming function all the way in with live view on a star and you will then see if there is any movement. Were you using a remote shutter release, the timer, or just your finger?
Has the astrotracer symbol shown up on the reat lcd along with the green gps symbol?
07-11-2016, 06:08 PM   #14
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QuoteOriginally posted by Grippy Quote
It's trial and error to find a combination that works well with the thing, I have had much better success at the long end and get clean exposures @ 300mm of up to 60 seconds whereas with the 10mm it seems to vary a lot.
A few things that have caused problems for me were the ground (how stable was it), were there any vibrations, even a little breeze can mess things up. Try the digital zooming function all the way in with live view on a star and you will then see if there is any movement. Were you using a remote shutter release, the timer, or just your finger?
Has the astrotracer symbol shown up on the reat lcd along with the green gps symbol?
Thanks for the response!

I have avoided using longer lenses because I wanted to get the 28mm working first, thinking it would be the easiest. I'll give some longer lens a try too.

I was using the timer for these but I have a remote to use if I ever get the astrotracer sorted out. Looking at my sample images I don't see any signs of vibrartion problems, only poor tracking. At 28mm I don't think this is a big issue but I'll be extra careful if I'm using 200 or 300mm.

Yes the astrotracer symbol and the green GPS symbol show in the rear LCD.

@Grippy What camera are you using?

Last edited by JimS_256; 07-11-2016 at 06:32 PM. Reason: Adding a question
07-12-2016, 07:33 PM   #15
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QuoteOriginally posted by JimS_256 Quote
Thanks for the response!

I have avoided using longer lenses because I wanted to get the 28mm working first, thinking it would be the easiest. I'll give some longer lens a try too.

I was using the timer for these but I have a remote to use if I ever get the astrotracer sorted out. Looking at my sample images I don't see any signs of vibrartion problems, only poor tracking. At 28mm I don't think this is a big issue but I'll be extra careful if I'm using 200 or 300mm.

Yes the astrotracer symbol and the green GPS symbol show in the rear LCD.

@Grippy What camera are you using?
By chance was the camera pointing up in the sky - with an elevation angle greater than about 45 degrees? If so, there appears to be a design problem where you are pointing high up in the sky that others have found.

I would try once again, with the camera level pointing out to the horizon and see how that works as a test.

Two weeks ago, I was out and shot a lot with an elevation angle of about 30 degrees up and things worked just fine.

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