First impressions: the Pentax O-GPS1

This little GPS unit is one of the reasons* I bought a Pentax K-5. Not only because it allows me to find true North or navigate to Pentax HQ in Japan (which you actually can do with this thing), but because of the Astrotracer function.

Basically, the camera moves the sensor to compensate for the motion of the earth relative to the stars in the sky. It's like having a tracking telescope mount... in your camera!

The mechanical components are all in the camera, thanks to the in-body shake reduction, but it needs a bunch of information from the O-GPS1; I'm guessing location, orientation and so on. Also focal length of the lens is important; a longer focal length means more perceived motion. Don't forget to set it on the camera if you're using a manual lens!

Plenty has been written about the device, so I won't do that. Here are some in-depth reviews if you feel like reading up on it, especially the PentaxForums one is thorough:

• ePHOTOzine
• PentaxForums

What I am interested in is what is most important: does it really work?

Even though the concept seems sound in theory, I was a little skeptical. Usually these ideas seems nice in concept but fail in execution. So I decided to try it out in the backyard. Here are two shots of Ursa Major side-by-side:

Two shots of Ursa Major:
one in normal bulb (left) and one with Astrotracer (right)

For both shots, the exposure time was 300 seconds (actually the left one was 294), aperture at f4.5, ISO 100 and focal length 35mm. Both images were post-processed in Lightroom with the exact same settings. I do apologize for the background light, it's pretty bad where I was standing. Light pollution not withstanding, the difference between the two shots is very, very clearly visible. I'm amazed at how good it works out of the box!


The stars in the O-GPS1 shot look a bit deformed, but I'm guessing that has something to do with the 5 minute exposure time, which was the maximum for this focal length. I'm pretty sure that shooting and stacking five 1-minute exposure shots will look even better.

Although this is a pretty imprecise test, the results are encouraging. I can't wait to get out to somewhere darker and really put this thing through it's paces, especially with the fast prime that's coming in tomorrow!

*= I might do a post on that later