Re: Poor quality of lunar images with 20D/C90

jess <jgates@xxxxxxxxx> wrote:
>I have a relatively new DSLR and an old (~ 1980, black tube) Celestron
>C90.

1200mm f13, in camera lens terminology. 90mm aperture Maksutov design.

> The other light I tried taking a picture of the full moon with
>the camera at prime focus (tripod, ASA 1600, 1/800, remote release
>after ~10 sec of MLU),

Try ISO 100 or 200.

> and the results were reasonably well-exposed
>but very fuzzy (and noisy: maybe ISO 200 or 400 would be better). I
>was using an Olympus Varimagni right angle finder attached to the
>camera. This gives a 2.5x magnification of the viewfinder, and I got
>the focus as sharp as I could. The view through the 20D viewfinder is
>horrible, though . . . I wish the screen had at least a small spot of
>fine-grained matte.

As you have discovered, good dSLRs really suck at astrophotography
because it is so hard to get a decent focus.

> There's a picture at:
>
>http://home.comcast.net/~jgates777/Moon.html

It's actually not bad. The C90 isn't a big scope and it simply isn't
possible to get tons of fine detail. With telescopes, aperture matters
a lot.

>I thought that perhaps the 'scope was damaged or had deteriorated in
>some way, but visual observations (30mm Kellner) look very sharp.

Your eye can compensate some for focusing errors.

> So,
>I have a few questions:
>
> 1. Is it normal for lunar astrophotographs to have much lower
>resolution than visual images?

The eye does a wonderful job of integrating images over time and
building up detail. The camera doesn't. One technique used is to
combine dozens of images into a much better composite.

> 2. Since the 'scope focuses "beyond infinity", it is very
>difficult to focus on the screen in a Canon 20D. Do you have any tips
>for manual focusing with a DSLR, or is it largely trial and error
>("Jeff R." at sci.astro.amateur recommended a Hoffman mask)?

Unless you can replace the focusing screen, or use an electric focuser
on the scope, what have is what you have.

> 3. The tripod I was using was an old, cheap Velbon (~$25 new) I
>bought for a video project, and is none too stable. If you touch the
>'scope at all the image dances all over the place.

Making it really hard to focus. (hint, hint)

> After some
>research, I've ordered a Bogen / Manfrotto 3246 with 488RC2 Midi
>Ballhead that will be used primary for daylight photography, but it
>hasn't arrived yet. Would you folks with experience expect this to be
>any better?

Don't know that tripod. The tripod I use on mine scope is pretty
solid.

>I understand that the 'scope is not the greatest,

Don't knock it. It's a fine scope.

> and this was my first
>try at lunar imaging, but my images look nowhere near as good as those
>I've seen from similar setups. I don't expect miracles, but these
>pictures are pretty sad. Any suggestions?

Don't take pictures of a full moon. It's boring. All the detail
washes out. Try the crescent moon.

--
Ray Fischer
rfischer@xxxxxxxxx

.

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