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Poor quality of lunar images with 20D/C90

 
 
jess
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      09-24-2005
I have a relatively new DSLR and an old (~ 1980, black tube) Celestron
C90. 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), 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. There's a picture at:

http://home.comcast.net/~jgates777/Moon.html

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

1. Is it normal for lunar astrophotographs to have much lower
resolution than visual images?
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)?
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. 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?

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

 
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dylan
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      09-24-2005
Whats the f number of the scope ?.
You should be able to expose the moon at approx f8, 1/250th with ISO 100.
You are right focussing can be difficult !


 
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Ray Fischer
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      09-24-2005
jess <(E-Mail Removed)> 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
http://www.velocityreviews.com/forums/(E-Mail Removed)

 
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Jim
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      09-24-2005

"jess" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> 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.

Why not get the tripod that Celestron sells for such a scope? It seems to
me that you are trying to get good photographs with equipment that is
totally inadequate (except for the scope that is).
Jim


 
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dylan
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      09-24-2005
Do you use mirror lock to stop vibrations ?


 
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Basiltoo
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      09-24-2005
"jess" <(E-Mail Removed)> wrote in news:1127585123.145180.137920
@o13g2000cwo.googlegroups.com:

> I have a relatively new DSLR and an old (~ 1980, black tube) Celestron
> C90. 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), and the results were reasonably well-exposed
> but very fuzzy


You might find this thread interesting:
http://forums.dpreview.com/forums/re...ssage=14611149

--
Regards,
Baz

 
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Christian Bonanno
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      09-24-2005
In article <(E-Mail Removed) .com>,
"jess" <(E-Mail Removed)> wrote:

> I have a relatively new DSLR and an old (~ 1980, black tube) Celestron
> C90. 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), and the results were reasonably well-exposed
> but very fuzzy (and noisy: maybe ISO 200 or 400 would be better).


Hey! I used to have a C80 when I was a kid! Tied it to a Pentax.

There is no need for that fast of ASA. I used to shoot 200 ASA and as
slow as 1/125 and get sharply exposed moon shots. That ASA speed is
probably where most of the fuzziness is coming from. Yeah, no need to
shoot at 1/800.

Also, the exposure for a mostly full moon like that is the same for a
sunny day (sunny/16).

What kind of DSLR and what mode are you in? JPEG or RAW?

look!
http://www.weasner.com/etx/guests/guests_moon.html

> 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. There's a picture at:
>
> http://home.comcast.net/~jgates777/Moon.html
>
> I thought that perhaps the 'scope was damaged or had deteriorated in
> some way, but visual observations (30mm Kellner) look very sharp. So,
> I have a few questions:
>
> 1. Is it normal for lunar astrophotographs to have much lower
> resolution than visual images?
> 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)?
> 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. 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?
>
> I understand that the 'scope is not the greatest, 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?





--

Photographs by Christian Bonanno
http://christianbonanno.com/
 
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jess
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      09-24-2005
Nominally it's about 1000mm f11, but I have read that the effective
aperture is more like f12.5 (as Ray Fisher suggests below). I'd
believe you about the exposure, but I read ISO 1600, 1/1800 from the
EXIF data and if anything the image looks underexposed.

 
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jess
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      09-24-2005
I understand that there is not a lot of aperture with the C90, but
I've seen other C90 shots via afocal methods that are far better.
The link that Basiltoo posted below, for example
http://forums.dpreview.com/forums/re...ssage=14611149
shows what I would call very fine detail from such a small scope.
Admittedly, it's not a full moon, and the shodw adds quite a bit of
perceived detail. I'll try a less than full moon next time and play
around with the ISO/exposure tradeoff. Perhaps the new tripod will
help. Thanks for the comments and suggestions.

 
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jess
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      09-24-2005
Well, I'm not really attempting to get into astrophotography with
this sort of telescope. I just thought a moon shot would be
interesting. Getting an astronomical tripod seems a bit of overkill
unless I'm attempting guided exposures of planets and deep space
objects. If I were going to do that, I'd probably figure out a way
to spring for a telescope with at least 8" of aperture. But, as I
said, I did spring for a substantially better tripod for terrestrial
work, and hopefully that will help a bit.

 
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