I just received the O-GPS1 unit last week and have been doing some astrophotography with it. I am basically just practicing in the city so that when I travel to a dark sky area, I will be familiar with the unit.
Some tips for astrophotography using the O-GPS1:
1. If you have your K-5 set up to turn itself off after a few minutes, you'll want to change this menu item for astrophotography. I use the K-5 accessory battery grip to make sure I don't need to change batteries.
2. Program dial needs to be set to Bulb
3. Autofocus has to be set to Manual
4. You will not be able to accurately focus the lens (especially a telephoto) by looking through the optical viewfinder. You'll see bright stars, but the screen is too coarse to see exact focus. Instead you'll want to use the LIve View at around 6x magnification. Find a star and very slowly rack the lens focus ring back and forth until you get the sharpest star image. (And for those who are wondering why not just set the lens on infinity, most lenses rack
past infinity to allow for thermal expansion and other tolerance-related issues.) You can lock your lens' focus with tape once you have true focus.
5. If it is really cold out, let your camera and lens acclimate to the temperature for awhile to stabilize thermal issues.
6. I've been experimenting with 20-50 second exposures with a M-200mm @ F4 and a FA-100mm Macro @ F2.8, and have been encouraged by the results. I'll have to wait until I get to really dark skies to go longer.
7. A right angle finder really helps if your camera is pointed up, otherwise it's pain to contort to see through the viewfinder. I use the Fotodiox model.
8. Make sure you use a sturdy tripod, and if yours has a hook on the center for hanging your bag or other weight, be sure to take advantage of that.
9. Turn off auto image review so that your view screen doesn't illuminate after each exposure. If you do have auto image review turned on, then turn off the blinkies.
10. A small red lens flashlight helps you see the buttons on the camera, and dropped items such as lens caps
Complaints:
1. The GPS unit has a blue LED that glows steadily when it has satellite lock. Unfortunately this light is right near the viewfinder, and it is really distracting when attempting astrophotography. A red LED would have been better. Cover it with tape.
2.It seems you have to control and initiate the exposure from the K-5 menu, which is awkward when the camera is pointing up. It would be nice if you could control subsequent exposure without having to go to the menu.
3. I wish there was a red "night vision" mode for the menu to preserve your night vision.
So far I am pretty happy with the unit. It seems to do what it claims, but I won't know how well until i get to some really dark skies.