The lens will certainly work, and being relatively fast at f1.7 it will work better than many others. The only caveat is whether it will frame the kind of shots you want. If you're accustomed to shooting with a 35mm SLR camera, this lens is roughly equivalent to your old camera with a 40mm lens on it, so this will not give you individual constellations, nor will it give you a complete canopy of stars. But it should be good for "a stary night over the valley" kind of shots (you can see a field of view sample here: http://www.dpreview.com/galleries/9037920827/photos/1594056 ). A tripod or some kind of stabilizer would definitely be in order. You might also want to consider either using the shutter timer, or a remote trigger to avoid vibration while taking your shots.
The focal length will give a "near normal" view (in 35mm equivalency terms); if you're looking to get a wide photograph of the sky you might require something wider, such as the Panasonic 14mm. However if a "normal" view is your goal the 20mm should be a very good choice. It gives quite sharp results.
Since the 20mm has no internal stabilizing system you might consider using a camera support, such as a tripod, for night sky exposures. Even a small amount of camera shake can impact a star shot due to the shutter speeds required.
Of course once you bring a tripod into the mix then the 1.7 aperture is less of an advantage (depth of field being ignored for the sake of discussion). The 14mm will give a wider angle view but, perhaps, be not quite as sharp as the 20 even if the 20mm is stopped down. (Of course you'll be focusing at infinity, so unless your plan is to print very large prints there may not be a discernible difference between the two lenses. Stars are small...from our viewpoint :-) ).
I would be totally comfortable using either lens (with appropriate support) for night sky shots but, since I have both lenses, I would prefer the 14mm over the 20mm due to the wider angle.
You might also consider the Rokinon 7.5mm fisheye, which gives a 180 degree view.
Absolutely! The f/1.7 aperture is very good at the low-light surroundings like the Strip. GH2 is a great machine for vedio, try it out with this lens and you will be happy for it. BTW, I didn't know the price dropped to $340!!
I used it in Maine a few months ago to get night sky shots and it worked well. You'll still need a long exposure (if I remember correctly, I was exposing for about ten seconds per shot). So a stable tripod is critical. But I was very pleased with the results.
Yes this lens will work and it is a very sharp so should give good results. As mentioned by other reviewers, the f1.7 lens is a very good low-light lens but I would still mount the camera on a tripod or other steady support for best low light results. At 20mm (40mm full frame 35) it is not a wide angle lens which will limit you horizon coverage and it will not bring distant object (stars/moon) in close. If you want to capture star trails again use a tripod and use your cameras bulb or other time exposure mode to allow for the earths rotation to give you the streaks of light (trails) a very nice effect.
Be sure to take a tripod; if possible, include some "foreground" objects, such as a hill or mountain. set the lens to f4 for maximum sharpness, use a shutter speed of 3 to 6 seconds. Before you go to Nevada, practice taking some night pictures at home or a nearby place first! Lou Toth
Will the 20 1.7 work for the night sky. The short answer is yes. The lens is sharp and is fast. No stabilization though and it is more or less a standard wide angle. The cost of the lens is low, when one considers the image quality and the fact it is a pancake, which is very convenient. I consider this a must have lens. Hope this helps.