Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-19-2013, 06:43 AM   #1
Site Supporter
Site Supporter




Join Date: Feb 2008
Location: Boston MA
Photos: Gallery | Albums
Posts: 297
Still Having Star Trails with O-GPS1

I tried the O-GPS1 on my Pentax K-5 and K-5ii, and was getting star trails regardless of how I calibrated it. Once, by accident I had an apparent good calibration on my K-5, but did not last. The compass noticeably bounced a lot anywhere I used it. So I replaced it and my new O-GPS1 has seems to have more stable compass behavior. However, I still have star trails, with any lens I use (Pentax 70mm, Sigma 105mm, Sigma 50-500mm @ 50mm and 200mm). My tests were 30 second exposures. I checked the level indicators on the cameras, and only the K-5 is a little off in the horizontal direction. Is it just hit or miss performance of using this O-GPS1 device? Does anyone have suggestions what I can do to improve my shots?
Thanks

08-19-2013, 07:20 AM   #2
Pentaxian




Join Date: Jun 2010
Location: North Zealand, Denmark
Photos: Gallery | Albums
Posts: 1,516
The two most obvious causes I can think of are:

1. Where and how do you use the O-GPS1? If you have magnetic materials on your mount or nearby, the compass may be fooled. Then the firmware will compute a false declination and you will get star trails. Not only should your compass reading be reasonably stable, but it should also be within plus/minus 10 degrees of the true geographical direction. I check once in a while on stars/planets at the time, I know they are culiminating.

2. A more sinister cause would be flaws in the camera body's sensor actuators. You wouldn't notice that in ordinary shake-reduction use, but it could be definitely be a problem in star tracking. You have tried on two different cameras (and I trust firmware has been up to date). Were the errors equally bad?
08-19-2013, 08:33 AM   #3
Site Supporter
Site Supporter




Join Date: Feb 2008
Location: Boston MA
Photos: Gallery | Albums
Posts: 297
Original Poster
Yes, the firmware is up to date. My replacement GPS seems better than the one I returned. I used it in an open field to about 20 feet away from my car to ensure metal objects wouldn't affect the compass. The trailing seems about the same on both cameras. I tried a couple of different lenses since the focal length information needs to be pretty accurate too. I am wondering that this O-GPS1 system just has too many variables that need to all be accurate to make things work, thereby limiting practical use for a relatively inexpensive system.
08-19-2013, 09:27 AM   #4
Pentaxian




Join Date: Jun 2010
Location: North Zealand, Denmark
Photos: Gallery | Albums
Posts: 1,516
Well, that's a tough one. You seem to be perfectly well aware of what you are doing, but allow me one silly question - and please don't take offence: You are doing "precise calibration" and not only "calibration"? Again, apologies for asking, but I have encountered others who overlooked that detail.

Second question: Do you always/mostly get trails or is it just once-in-a-while?

I have used my O-GPS1 for more than a year on a K-5 with many lenses and without severe, consistent problems. So, I may not be the right one to advice on further trouble shooting, but here are a few things you might try, anyway, (or you may have tried already):
  • Avoid zooms. The way they report their focal length may not be too accurate.
  • In fact, I am afraid that even not all prime focal lenses live up to specs so find those of yours that give the best results.
  • Wen you encounter trailing, try to do the precise calibration again with your lens pointing in different directions. The number and positions of available GPS satellites change all the time and it is my experience that such re-orientation will often be helpful.
  • On any night try to photograph in different geographic directions; some directions will often work better than others for me.
I do hope, you will find a solution, because - when it works - the O-GPS1 is such a wonderful thing. It is by no means 100.00% reliable, but it is so easily portable and redy to use that it has already given me more good/acceptable images in one year than I could ever find the spare time to get during the same year with my heavy, polar alignement requiring equatorial mounts.

08-19-2013, 10:46 AM   #5
Site Supporter
Site Supporter




Join Date: Feb 2008
Location: Boston MA
Photos: Gallery | Albums
Posts: 297
Original Poster
Indeed I start with the calibration first, followed by the precise calibration. I am getting trails most of the time. Once in a while.. (5-10% of the time so far) I got perfect tracking. Indeed the orientation seems to make a difference. I figured the focal length info is not very accurate on zooms, and therefore used a number of primes.

I am thinking or returning the O-GPS1, perhaps it is too finicky.... For the same price there is this mount: Orion StarBlast AutoTracker Altazimuth Mount | Orion Telescopes and Binoculars That may work more reliably... Although, it does state in the manual that even after aligning the scope, that objects could still slowly drift. Right now the "drift" on my O-GPS1 is about 5 times better than having no tracking. I was hoping for a factor 20.....
08-19-2013, 12:56 PM   #6
Pentaxian




Join Date: Jun 2010
Location: North Zealand, Denmark
Photos: Gallery | Albums
Posts: 1,516
QuoteOriginally posted by Eric Seavey Quote
I am thinking or returning the O-GPS1, perhaps it is too finicky....
I understand your thinking. This just doesn't sound right.

Now, you haven't shown any sample pictures, but something like this, is what I regularly - though certainly not always - get with my 200mm lens(es) and 20s of exposure time:



OK this is a stacked, processed image - but it's a 100% crop and the trails are what you see on every individual exposure.
08-20-2013, 08:46 AM   #7
Site Supporter
Site Supporter




Join Date: Feb 2008
Location: Boston MA
Photos: Gallery | Albums
Posts: 297
Original Poster
Last night I spent a little time with other lenses and finally got decent results with 1-minute exposures with 21mm, 40mm, 70mm (first attached 100% crop is what I get 30% of the directions I shoot) and a Sigma 30mm. OK results with Sigma 105mm. Useless results with my Bigma 50-500mm @100mm, but would be more similar to your photo at 20 seconds exposure...see second attached 100% crop. It got cloudy and so I wasn't able to test it with my K-5ii. I am planning on using the K-5 for astrophotography anyway, so it is OK. Seems like I need to switch to the new Orion Starblast mount, that I can use with any lens and point in any direction, even though it is not as portable as the O-GPS1. They are both the same price....

Attached Images
View Picture EXIF
PENTAX K-5  Photo 
View Picture EXIF
PENTAX K-5  Photo 

Last edited by Eric Seavey; 08-20-2013 at 09:05 AM.
09-02-2013, 11:52 AM   #8
Junior Member
Gooj's Avatar

Join Date: May 2010
Location: Sweden / Lappland
Posts: 27
I've also seen it at least once that the compass have been flying all over. Though, it didn't seem to affect my starhunting game. Maybe I did another calibration that fixed it, can't remember.
I just calibrate my camera (make sure I got the 3D satellite icon) then put it on my tripod and start shooting. It have been working like a charm since I got the O-GPS1 and used it on my K-5 IIs.

Really sad it doesn't seem to work too well for you.
09-14-2013, 02:08 PM   #9
Junior Member




Join Date: Sep 2012
Location: Near Paris
Photos: Gallery
Posts: 43
@Eric
Perhaps you've got a bad copy again. If you got star trails with 105 or 70mm lens and short exposure time (30s) most of the time (let say >75%) you should return the GPS unit to Pentax. But don't hesitate to perform again the precise calibration if your results are bad. Sometimes the calibration have failed even if the camera say it's ok.
However, using a zoom lens is a very bad idea since focal length information may be not reliable enough for a precise tracking.
Nevertheless, most of us using this GPS are quite satisfied with it.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
compass, k-5, o-gps1, pentax, sigma, star, star trails, trails, tripod
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
First time experimenting with star trails Victor101 Photographic Technique 2 05-27-2013 09:45 AM
Pentax O-GPS1 GPS Unit with K-01 i_trax Pentax K-01 2 12-03-2012 06:49 AM
Problems with O-GPS1 NickW Pentax K-5 & K-5 II 6 03-27-2012 03:22 AM
O-GPS1 - How is this works with moving + stationary object? LFLee Pentax Camera and Field Accessories 12 09-30-2011 12:42 PM
Star Trails With DSLR Barnster Photographic Technique 22 08-11-2009 09:53 PM



All times are GMT -7. The time now is 05:47 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top