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Hi Scott,
Yup, that was too much magnification on the moon.
Even if the scope could give sharp projection images at that power and focal
ratio, atmospheric turbulence and vibrations in the mount and camera will be
working against you.
1.) Make sure your scope is well collimated at a
high power. If it isn't, you'll never get the best out of it.
2.) Can you lock up your camera's mirror? Are you
firing the shutter with a cable release? I find it's best to lock up the mirror,
then use the self timing feature of the camera to trip the shutter without me
touching the system for a several seconds, leaving only the shutter itself
as a source of vibrations. Using the "hat-trick" technique is an even better way
if the exposures are 1/4 second or more, as that would eliminate the shutter
vibration effects.
3.) For eyepiece projection, stick with eyepieces
in the 15 to 25mm range. This will still get you good magnification, and a more
reasonable f-ratio than what you were trying before. You can always enlarge an
area of a sharp photo for the magnification effect you wanted in the first
place.
4.) For prime focus shots, knife edge (or Ronchi
grating) focusing on a star is the way to go. However, for eyepiece projection
photography, it's almost impossible to find the "right spot" in the resulting
shadow pattern with a knife edge. The best way here is to use a Hartmann
mask on a bright star. Ron Wodaski has a good page on Hartman masks with sample
star images at: http://www.newastro.com/newastro/book_new/c2_d.asp
Remember that it's usually best to finish focusing
an 8"SCT by turning the knob CCW, as this pushes "up" on the mirror thus taking
up any slack in the focusing mechanism.
Hope this helps.
----- Original Message -----
Sent: Monday, September 03, 2001 12:24
PM
Subject: [APML] Lunar Photography
I have just experienced one of the more
frustrating lunar photography sessions of my short life and have a couple of
questions about the whole experience.
I have been using an 8" Meade
LX-200 and a Canon ELAN II (35mm SLR) doing prime focus (camera mounted
directly to the telescope with out an eye peice) and am finaly starting to get
some good results (for your viewing pleasure some of the more recent shots can
be found at http://www.manetheren.net/night). Focusing was a little off at first, and then I had some
issues with camera shake (the mirror wasn't tripping up prior to shooting) but
finaly worked those out.
So I figure I'm ready to try some eyepeice
projection. I throw in a 26mm super plossl (f/28.4), and right off the
bat I notice I can't find that "sweet spot" in the focus where everything is
crystal clear. As my camera's meter is fairly sensitive, I bracket some
of these shots on focus instead of shutter speed.
Then I decide to go for the gusto and throw in
a teleview 4.8mm Nagler (f/198.5). I couldn't even come close to getting
things in focus. Same results with my 9.7mm Super Plossl (f/94.3).
Everything is just a fuzzy gray and brown blur. I tried extending my
tele-extender all the way out and all the way back in. Didn't make a
diffrence.
I guess what I'm realy wondering is if those
focal ratios (and attendant maginifcations) are simply beyond the ability of
my scope and camera to handle.
Thanks,
Scott
"God does not play dice with the universe; He
plays an ineffible game of his own devising, which might be compared, from the
perspective of any of the other players, to being involved in an obscure and
complex version of poker in a pitch dark room, with blank cards, for infinite
stakes, with a dealer who will not tell you the rules, and smiles all the
time." -- Gaiman and Pratchett
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