M57 with DSI

http://tinyurl.com/4oet7

Starting to get used to this thing..

On Fri, 10 Dec 2004 13:46:28 GMT, "Chris Taylor"
wrote:

http://tinyurl.com/4oet7

Starting to get used to this thing..

Indeed you are :-) .

If I were to offer any comments on your image Chris, I'd say that the
stars would suggest you didn't quite reach focus. How are you trying
to achieve focus? Eyeballing it?

Focus is a major problem. I have numerous sequences of images that,
although they looked great in the camera's view finder, were fuzzy
under closer inspection.

Does the DSI plug into a laptop and you preview your images there?

--
Pete
http://www.digitalsky.org.uk

"Pete Lawrence" wrote in message
...
On Fri, 10 Dec 2004 13:46:28 GMT, "Chris Taylor"

If I were to offer any comments on your image Chris, I'd say that the
stars would suggest you didn't quite reach focus. How are you trying
to achieve focus? Eyeballing it?

Does the DSI plug into a laptop and you preview your images there?



Hi Pete

Thanks for the constructive critisism.

I'd have to rule focussing out of the equation as I've got an electronic
focusser that is controlled from the laptop upon which the image is
displayed. The arrangement is focussed first with one or two stars prior to
fine focussing on the object. This is the same method used with the LPI on
Saturn and the Moon recently: http://tinyurl.com/4qvdc

Hazard-ing a guess at the causes I'd go for.

a) Post Processing. I'm still getting the hang of this and am using Paint
Shop Pro. I'm guessing that overprocessing owing to limited exposures is
contributing.
b) Image rotation. Although not too prevalent, I'm using an equatorial mount
and am forced to take limited exposures with limited amount of stacking. I
intend to try registax to see how many images stacked that I can get away
with but the stars toward the outside of the original image do look a little
extended with longer exposures. Santa has been petitioned for an equatorial
wedge and I've already got the guide-scope and guide-camera.
c) You get what you paid for? The imager comes in at $299 (£156 at today's
rate). Meade's promotional images website show similar bloating (not as bad
as mine though...) see he http://tinyurl.com/44m6a

I'm still pretty chuffed that the price has allowed me to take anything from
the deeper sky and will probably use this imager as a stepping stone to a
better camera, later. In the meantime I'll be stretching myself and the
camera to the limit while trying to cop the messier list at the least.

Thanks for looking

Regards

Chris

On Fri, 10 Dec 2004 16:26:26 GMT, "Chris Taylor"
wrote:

Thanks for the constructive critisism.

I'd have to rule focussing out of the equation as I've got an electronic
focusser that is controlled from the laptop upon which the image is
displayed. The arrangement is focussed first with one or two stars prior to
fine focussing on the object. This is the same method used with the LPI on
Saturn and the Moon recently: http://tinyurl.com/4qvdc

Hmm - the Saturn image shows quite a bit of detail doesn't it. The
moons look pretty sharp in that image too. I'd look at the moons as a
focus reference.

How sure are you that your electronic focusser is getting it right?
Can you adjust the focus while the imager is taking it's pictures? If
so, take a picture of a brightish star. Drop the star to the edge of
the field, turn the drive off and adjust the focus one way as the star
drifts through the field. You should get a line that thins down and
fattens again as you move into focus and out again. Having said this
- I've never actually done this ;-) !

At least this method would tell you how thin you can go. Then compare
this with the focusser's best shot.

Hazard-ing a guess at the causes I'd go for.

a) Post Processing. I'm still getting the hang of this and am using Paint
Shop Pro. I'm guessing that overprocessing owing to limited exposures is
contributing.

A very easy mistake and one I still make. Are you doing anything to
spread the images though?

b) Image rotation. Although not too prevalent, I'm using an equatorial mount
and am forced to take limited exposures with limited amount of stacking. I
intend to try registax to see how many images stacked that I can get away
with but the stars toward the outside of the original image do look a little
extended with longer exposures. Santa has been petitioned for an equatorial
wedge and I've already got the guide-scope and guide-camera.

Yes that could spread them but the field doesn't look that rotated to
me to be honest.

c) You get what you paid for? The imager comes in at $299 (£156 at today's
rate). Meade's promotional images website show similar bloating (not as bad
as mine though...) see he http://tinyurl.com/44m6a

Don't do it down - check out the other factors first.

I'm still pretty chuffed that the price has allowed me to take anything from
the deeper sky and will probably use this imager as a stepping stone to a
better camera, later. In the meantime I'll be stretching myself and the
camera to the limit while trying to cop the messier list at the least.

Good luck :-)
--
Pete
http://www.digitalsky.org.uk

Pete Lawrence wrote:
[snip]
If I were to offer any comments on your image Chris, I'd say that the
stars would suggest you didn't quite reach focus. How are you trying
to achieve focus? Eyeballing it?

Focus is a major problem. I have numerous sequences of images that,
although they looked great in the camera's view finder, were fuzzy
under closer inspection.

Out of curiosity Pete, how do you focus? I've found it's rather tricky
getting it spot on. Looking through the viewfinder and using a hartman
mask are OK, but I never seem to get it quite spot-on. I suppose
shooting tethered (now I've worked out how to) and trying to make the
star images as small as possible is one way.


Tim
--
This is not my signature.

On Fri, 10 Dec 2004 18:36:29 +0000, Tim Auton
wrote:

Out of curiosity Pete, how do you focus? I've found it's rather tricky
getting it spot on. Looking through the viewfinder and using a hartman
mask are OK, but I never seem to get it quite spot-on. I suppose
shooting tethered (now I've worked out how to) and trying to make the
star images as small as possible is one way.

Depends what's up and about Tim. I have used DSLRfocus in the past.
It's a good program and works with a number of DSLR cameras to help
you achieve focus. It's pretty cheap too and the author, Chris
Venter, is a really friendly chap.

When I can't be bothered to drag the laptop outside, it's down to
eyeballing. Masks are all very well but they tend to cut out a lot of
the available light making focussing just as tricky.

I move the scope to a bright object and focus it through the camera's
viewfinder. I make a number of passes through the focal plane so I
get a feel for where the focus is. Once I've done this, I apprach the
focus from one direction (out to in - i.e. shortening the focusser)
and stop it short of the focal point. I then proceed to take short
exposures of faint stars, displaying and max zooming the results. I
tweak the focusser in by a very small amount (and I mean small -
sometimes it doesn't even feel like the focusser has moved!) and keep
checking the star sizes.

Takes a few minutes but seems to work.

Not something to do when tired though!

--
Pete
http://www.digitalsky.org.uk
Home of the Lunar Parallax Demonstration Project

Pete Lawrence wrote:
On Fri, 10 Dec 2004 18:36:29 +0000, Tim Auton
wrote:

Out of curiosity Pete, how do you focus?
[snip]
Depends what's up and about Tim. I have used DSLRfocus in the past.
It's a good program and works with a number of DSLR cameras to help
you achieve focus. It's pretty cheap too and the author, Chris
Venter, is a really friendly chap.

Sadly Windows only and I have a Mac laptop. OS X and Apple hardware is
lovely, but not particularly well supported for amateur astro work
(IRAF is a touch heavyweight for a few snaps of the moon!).

Perhaps I'll write something if Canon update their SDK to support the
20D and approve me as a developer.

I move the scope to a bright object and focus it through the camera's
viewfinder. I make a number of passes through the focal plane so I
get a feel for where the focus is. Once I've done this, I apprach the
focus from one direction (out to in - i.e. shortening the focusser)
and stop it short of the focal point. I then proceed to take short
exposures of faint stars, displaying and max zooming the results. I
tweak the focusser in by a very small amount (and I mean small -
sometimes it doesn't even feel like the focusser has moved!) and keep
checking the star sizes.

That's pretty much how I'm doing it, but in a marginally less refined
way. OK, I just twiddle the knob till it looks about right


Tim
--
This is not my signature.