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Sunday, December 04, 2005

Satellites, star trails and nebulae

They might be hard to see, but this image of the Orion Nebula and the belt stars of Orion also show a few geosynchronous satellites. My Canon 20D was set on a tripod with my 70-300mm zoom set to 70mm. Stars trailed in the 30 second exposure while the geosynchronous satellites are stationary on the frame and appear as faint stars. Trouble is, the cameras detector generates similar looking noise, but luckily the (at least) 3 satellites all appear in a straight line and are white in color. Two of the satellites are on the lower right edge of this frame very close together and are aligned roughly with the star trails. The exposurfe was 30 seconds at f/4, ISO 1600. Posted by Picasa


Shayan said...

Those are some great star trails! Have you run into problems with focusing in the dark? Whenever I try taking pictures in low light situations, I have trouple getting the auto-focus to work right.

Just wondering if you've run into any such situations...

Jim said...

Hi Shayan,
Yes, I have had trouble focusing. Mostly, I use my Sigma 24mm f/1.8 lens which has a focus scale on top and I experimented a bit to try and find the best focus for infinity and just set it there manually. It is quite sensitive (especially at f/1.8!), however and I get slightly inconsistent results, but they haven't been all that bad. I haven't used the kit lens because it does not have a focus scale, though if something bright is available in the distance (city lights, Venus, the Moon, etc.) you might be able to use that to focus. I've also found my 70-300mm zoom to have some trouble focusing except that at 70mm focal length, infinity appears to be against the hard stop at the infinity end, so I've managed to get some decent results there (but less good at 300mm focal length...). Definitely a challenge, but practice helps, that's for sure! Do you have a lens other than the kit lens? If not, I'd recommend a faster lens like an f/1.8 or f/2.8. The 24mm isn't quite wide enough, I've found, though not bad. I'd love to get a 14mm f/2.8 lens, for example. BTW, I tend to manually focus, though with my 24mm lens, I leave it in AF which gives me some resistance and keeps the focus from shifting afterwards. I also run my Canon 20D with custom function 4 set to option 1 (AE lock/AF) that puts the focus manually on the * button and keeps it from doing any AF when you press the shutter (or cable release in my case).

Good luck!