[AZ-Observing] First Light for Fisheye Lens

  • From: Tom Polakis <tpolakis@xxxxxxx>
  • To: evac@xxxxxxxxxxxxxxxxxxxxxxx, az-observing@xxxxxxxxxxxxx
  • Date: Sun, 07 Mar 2004 11:03:30

Hi all,

After extensive shopping on eBay, I found an 8mm f/4 Sigma fisheye lens for
my digital SLR camera at a reasonable price.  The location was reasonable
as well: Monument Camera in Tucson.  We took the alternative way back to
Tempe through Florence, and detoured to the Picketpost Mountain trailhead
last night for some trials.


A full-frame fisheye lens for a 35mm camera is typically around 15mm focal
length, but the "zoom factor" associated with the Canon Digital Rebel's
smaller chip requires an even wider lens.  The angle across the diagonal
*should be* 180 degrees, but I was disappointed to learn that mine was
giving about 150 degrees, and was hardly full-frame.  I had to get home to
realize that a lens hood was cropping the coverage of the lens.  Well,
that's why we do trials.

The depth of field of an 8mm lens is nearly unlimited, so the people in the
images are only a foot or so from the lens.  The middle example best
demonstrates the field of view; note Venus and Procyon in the frame with
much room to spare.  And this was before I discovered the lens hood effect.

All of the images are 30-second exposures wide open at f/4 with the ISO set
to 800.  A couple suffer from JPEG overcompression on my part, and the ISO
could probably be bumped down to 400, but they're only trials.  I can't
wait to use this lens for more astronomical scenes in the future.


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