Zuiks;
I'm glad Dirk found this site. These photos are spectacular (about 2
orders of magnitude better than anything I did with Hale-Bopp) and I've
seen Dan Norris' work before and like it a lot.
But also, these photos illustrate why some lenses are better for this
type of photograph than other lenses are (assuming one wants minimal
distortion and maximal blow-up capability). And also illustrates why
sharpness and contrast testing don't tell the whole story.
The photo on the left is taken with a 50/1.4 wide open for 45 seconds.
Stars will trail just a bit on a 50mm for this length of time. My 'star
tests' indicate this lens has plenty of coma and other distortion until
at least F/2.8 If you click on the left photo so it enlarges, you'll
see what I mean. Notice that some of the dimmer stars, especially close
to the center, are just trailed slightly - they look like short lines
instead of points. This is normal. Now, look at the brighter stars,
especially closer to the edges. Whoa! They look like blobs or birds or
... little comets, don't they? This is coma. This is bad. Personally I
avoid the 50/1.4 (and 50/1.2) wide open for these shots. Course, the
trade-off is longer exposure time and longer star trails.
Now, enlarge the right hand photo, taken with th 90 macro at F/2. In my
tests, this lens was free of any distortion even when wide open. Dan's
photo illustrates this, too. The stars are a little more elongated than
the 50/1.4 shot, due to appx same exposure time but almost twice the
focal length. But they're not distorted. The 90/2 (and 50/2) are great
wide open for this work.
George
Dirk Wright wrote:
>
> http://www.jpl.nasa.gov/comet/norris2.html
>
> it's great to see people using these cameras!
>
> Be seeing you.
>
> Dirk Wright
>
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