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Re: [APML] Getting Started
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>>>>> "parker" == Parker Parrish <Parker_Parrish@mindspring.com> writes:
parker> And finally, assuming a relatively dark sky (mag 5.5 or
parker> so), what's the typical skyfog limit with a 50mm lens
parker> shooting at f/2.4 on E200?
FWIW, my experience matches Jon Kolb's pretty well WRT E200 and sky
fog. Under dark skies (approx mag 6), I've had good luch with
exposures of 30 min at f/4. Depending on just how dark it is and what
the altitude of the object, times run anywhere from about 20--40
minutes at f/4 with no pushing.
And, like Jon, I'd recommend you try a set of test shots out to about
f/5.6 to see how the sharpness looks in the corners. My f/1.4 50mm
lenses need to be shot at f/3.6 or slower. At f/2.8 they're okay for
low res scans for the web. They're marginal for an 11x14 enlargement
(it works because I crop off the extreme corners which don't look very
good).
If your lens has detentes at half-stops, try a series of shots to see
what works. Unlike your "real" shots, the test shots can be a bit
underexposed. Just point at a relatively rich area of the sky so you
have lots of stars across the field. Figure 10 minutes at f/4 and
scale (14 at f/4.8, 20 at f/5.6, etc.). I shot all the way down to
f/1.4 with mine just to see how bad it gets down there (real bad).
Do this once and stick the results in your notes and you never have to
guess how the lens performs anymore.
regards,
roland
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PGP Key ID: 66 BC 3B CD
Roland B. Roberts, PhD RL Enterprises
roland@rlenter.com 6818 Madeline Court
roland@astrofoto.org Brooklyn, NY 11220
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