Saturday, November 10, 2007
Comet Holmes Update
We've been watching comet Holmes each night. It seems easier to see now, even though it has dimmed slightly from magnitude 2.9 to magnitude 3. Even with the naked eye, it seems to have grown in diameter and now looks distinctly fuzzy.
It's really fuzzy in binoculars. I shot this picture with a 85 mm lens, so it shows a "zoomed in" view compared to the picture I posted earlier, which was shot with a 24mm wide angle lens. I stacked a number of 4 second exposures at F2.8 and ISO 1600 for this image. There was some coma in the corners of the image, which I have cropped out, so I'll probably be trying this lens at F4 next time out.
The original size images showed that the stars moved during the four second exposure, but after I scaled the picture down for the Web, the stars look ok. I was able to shoot eight second exposures with the 24m lens, but four seconds is a little too long at 85mm. The more of a telephoto lens one uses, the more the earths rotation streaks the star images, and the more one needs to get out the good old motorized telescope mount to track the stars during the exposure.
Posted by Brad