Reader's Comments - Index of - Free

Star Streak Tutorial
magnification, a 10" diameter scope will display objects at four times the brightness of a 5" scope at the
same magnification. This is probably where the confusion arose.
-- Vince Farnsworth, September 23, 1997
Regarding long exposure star trail photography with camera lenses, remember that in a lot of climates
moisture will condense on the lens surface as the temerature drops to dew point. So, your 6 hour shoot
will be ruined by the lens fogging unless you take care to heat the lens element with a "dew chaser"
assembly. The Kendrick system, http://kendrick-studio.com, is the best commercially available, or you
can make your own using resistors and wire connected to a 12 volt battery source. Consult Sky and
Telescope magazine archives for articles on this subject. The object is to keep your lens surface just
above the dew point so it will stay moisture free.
-- Greg Palman, May 30, 1998
When the objective is to image faint stars, the aperture settings and focal settings are critical. Significant
improvement will likely occur when optimal settings are used. Usually more sensitivity will be achieved
by stopping down the aperture somewhat as reduction in illumination is more than offset by a reduction
in the circle of confusion (ie less light but more tightly imaged).
As for focus, while the factory scale is "good enough" for most purposes, the true infinity focus is often
different slightly than that indicated. Experimentation pays dividends.
If no time to experiment, a rough guideline is to reduce apperture 1 stop from wide open.
For the curious, the circle of confusion will be reduced as the aperture is closed more than optimal for
the above purposes until diffraction effects about the aperture edges add disproportionate degradation.
For a typical 50 mm lens, the smallest circle of confusion is found about f/8.
-- John Ohrt, October 28, 1998
Since no one mentioned it, I'd like to add a quick comment on photographing (or just observing) the
moon. The least "interesting" time to do it is during full moon. Since the light of the sun hits the moons
surface almost straight on, you won't have the shadows that bring out surface detail like mountains and
craters. Half and quarter moons are much more interesting because you can see more of the features of
the terrain.
-- Frank Wortner, March 24, 1999
When's sunset? Where's the moon? When's the sun gonna come up? ...Get a Casio Fish-En-Time or
Forester for $39 and you'll always know. Just punch your lat/lon into it and it tells you all that and even
a graph of where the moon should be right now (if you're indoors and thinking about getting ready to
http://www.photo.net/astro/star-streak (4 of 9)7/3/2005 2:15:29 AM