Re: [APML] planetary photography

["John Boudreau" <jeboud@mediaone.net>]

----- Original Message -----
From: Mark Park <mark_park@hotmail.com>
To: <astro-photo@seds.org>
Sent: Tuesday, January 15, 2002 9:32 AM
Subject: [APML] planetary photography


> I can't seem to get good images of the planets.
>
> My first question is how do you focus for eyepiece projection.  Can I
setup
> the projection, move to a star and knife edge?  I know I can't knife edge
on
> the planet since it is not a point source.  Planets are much closer than
> stars (to understate the obvious), but are they at the same focal point
for
> the eyepiece projection?

Mark, knife edge focusing is nearly impossible to interpret at the focal
ratios usually used for planet film pics. Probably the best method is
focusing on a nearby bright star with a Hartmann mask, then going back and
framing the planet. A Hartmann mask is easier to read than a knife edge, and
while the knife edge enjoys a definite advantage in accuracy when used at
typical astrophoto f-ratios of f/10 or faster, that advantage disappears in
the typical f/30 to f/70 used for film planet imaging as the depth of focus
becomes noticeably deeper and more forgiving. And yes, both the stars and
planets are at infinity focus --- the moon and sun too.

>
> Second question...  How much should I crank up the magnafication from the
> projection (ie distance of camera from eyepiece)?  from the eyepiece (ie
> 24mm vs 8mm)?  Is one method better than the other?

What kind of scope and adapters are you using? Do you have a variable length
eyepiece projection adapter? I'd tend to believe that using a quality,
higher power e.p. is better than projecting further with a lower power one.
But what works for someone else may not work as well for you. I think you're
going to have to experiment.


John Boudreau
jeboud@mediaone.net
http://people.ne.mediaone.net/jeboud/astro.htm


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