Just got home, photo from Twisted Shoe Campsite

[JeffB]

Nice shots! The star shots came out exceptionally well.

...I shot these images with a fast 20mm lens at f/1.8 to f/2.4, for about 20 seconds each...

That's a Sigma, right? They make a series of f/1.8 lenses in 20, 24, & 28mm. I've been wanting a fast, wide prime like that, particularly for shooting the night sky 

How do you like the 20mm?

Yes, the Sigma 20mm f/1.8.  I rented the lens for two weeks at cost of about $75 including shipping. 

Not totally impressed with it overall.  I love the speed @ f/1.8 but not very sharp until you get to f/2.8.  A pet peeve of mine for pictures of star fields is inaccurate infinity focus.  Autofocus is just about useless on the stars (too dim and small in the finder) so I rely on the lens' ability to stop at infinity focus when the ring is turned all the way in that direction.  This particular lens will go past the infinity mark and therefore really hard to find perfect focus on distant and dim objects.  The edges suffer as you can see on the second  Milky Way shot, the brightest star is Jupiter and has bad CA and is bulging toward the center. 

OTOH, the speed is awesome and the focal length is just about perfect. It did a pretty good job, much better than my buddy's Nikon ED VR 18-200mm f/3.5-5.6.  His lens was not nearly fast enough shooting at night especially the stars.  His camera (Nikon D40X) has way too much "ampglow" for shooting over 30+ seconds exposure of the night sky. 

[tjavery]

Yes, the Sigma 20mm f/1.8.  I rented the lens for two weeks at cost of about $75 including shipping. 

Not totally impressed with it overall.  I love the speed @ f/1.8 but not very sharp until you get to f/2.8.  A pet peeve of mine for pictures of star fields is inaccurate infinity focus.  Autofocus is just about useless on the stars (too dim and small in the finder) so I rely on the lens' ability to stop at infinity focus when the ring is turned all the way in that direction.  This particular lens will go past the infinity mark and therefore really hard to find perfect focus on distant and dim objects.  The edges suffer as you can see on the second  Milky Way shot, the brightest star is Jupiter and has bad CA and is bulging toward the center. 

OTOH, the speed is awesome and the focal length is just about perfect. It did a pretty good job, much better than my buddy's Nikon ED VR 18-200mm f/3.5-5.6.  His lens was not nearly fast enough shooting at night especially the stars.  His camera (Nikon D40X) has way too much "ampglow" for shooting over 30+ seconds exposure of the night sky. 

Bummer. I've read about the softness in reviews of the Sigma f/1.8 wide angle primes. I'd love to have a wide prime that was decently sharp at nearly wide open. I used to have the Canon 28mm f/1.8 and it was about the same - noticeably soft until stopped down to f/2.8 or smaller.

The infinity focus thing is a big gotcha. It irritates me that actual infinity isn't defined well. But from what I've read, the actual point of infinity focus varies as temperature fluctuates (i.e. the parts inside the lens expand or contract due to temp flux). Most modern AF lenses will go way past infinity.

The best solution is to use a camera with Live View. Just zoom in 10x on the LCD screen and fine-tune the focus.  I've done this on my 40D, and it's the best way to focus on stars (manually, of course).

I just read an interesting post about ampglow on NSN:
http://www.naturescapes.net/phpBB3/viewtopic.php?f=1&t=139131

I never realized the 5D was so bad. That explains the red crap I got in my 24-minute exposure that I made on my recent trip to the park   

[SA Bill]

Jeff:
I shot a couple of star pics with a Minolta 58mm f/1.2 this past week. Talk about CA!! I'll post a pic sometime this weekend so you can see it. The lens was on an adapter to allow it to work on my Sony a100 so the adapter optics might have contributed some of the problem but I think most of it was from the lens.
   Bill

[Roy]

Bill, the glass in those adapters is notorious for producing that kind problem.  There's a guy over at Dyxum.com that modified a 58/1.2 by replacing the MF lens mount with one that fit the AF mount on his camera with really nice results.
Or you can get an adapter without a glass element.  Check the link;  Haoda Fu has a good reputation.  I've got one of his chipped adapters for using M42 mount lenses on my cameras and I've been pleased with it.  His stuff is pricey, but that's a really nice lens.  Be nice to be able to us it.

http://haodascreen.com/minoltaMDAF.aspx