View Full Version here: : M17 Nebula with Canon 20DA
30-08-2005, 09:27 PM
Hi Folks....been trying to get this one for the last week but the weather has not been kind to me.
I am having problems guiding with guidedog so I gave up tonight and just went back to doing some more 30 second exposures...total of 15x30 second exposures combination of 800 & 1600 ISO stacked in K3ccdtools and edited and croped in Photodeluxe.
Used my C11 F10 2800FL and Canon 20DA
30-08-2005, 09:30 PM
Looks like you're having fun Tony:) Nice shot, but this one looks alittle out of focus, the details not as sharp as your last couple. What do you use to help you focus?
30-08-2005, 09:34 PM
lots of nebulosity and detail though :)
30-08-2005, 09:38 PM
Paul I just use the live view on the Canon 20DA LCD screen to focus...you can zoom right in aswell while your focusing....its very easy to get focus but I must say I did do the focus earlier on in the night so the scope may still of needed cooling down....also I may have stacked a fairly ordinery image instead of using only the best images for the final stack....maybe the best 10 instead of all 15.
30-08-2005, 09:48 PM
As your scope cools down the focus will shift. If you move your SCT, sometimes even only small amounts, the focus will shift. Do you only focus once in the night and don't refocus it again?
30-08-2005, 09:55 PM
Yep only once Paul...I have trained my scope to stay focused at all times no straying allowed....lol
I have taken out 2 ordinery frames and restacked 13 instead of 15...I think its a bit sharper now...what do you think....and yes I will refocus more often...
I removed the old pic with the new edited one in original post above.
30-08-2005, 10:06 PM
I get an "Invalid attachment specified" when I click on the new link Tony
30-08-2005, 10:07 PM
30-08-2005, 10:08 PM
31-08-2005, 06:49 AM
Very nice image! What's you problem with guidedog? What is your guiding setup?
I played with Guidedog the other night, and while it "is" a bit of a dog (compared to K3ccdtools) I was able to get it working, so perhaps I can help??
First question is.. Did you have the star "aligned".... Ie RA movements going left-right and DEC movements going up-down. It is crucial to get this as acurate as possible.
31-08-2005, 07:15 AM
nice stuff there Tony! you are doing a great job!!
31-08-2005, 08:26 AM
Nice shot Tony !
31-08-2005, 02:14 PM
My settings below.
2 second exposure as my Stellcam takes around 2 second for each exposure
yes I have set it up correctly so NSEW goes in the right direction
Guiding parameter's from top to bottom
24,15,15,10,1.5 and 0 for both backlash settings.
I even used a 3 x barlow at FL1800 on me ed80 and still is not accurate enough....I have no problem keeping the star in the inner circle but it move around within too much....what I dont understand is even though it stay's in the inner circle hour after hour I notice my image's are slowy going south..this makes no sence to me...it may be moving around within the circle but its not moving...how could my image area be moving if it's staying within the inner circle even at 1800FL...?????????
Any help appreciated.
31-08-2005, 02:26 PM
What you have is classic symptoms of field rotation error. You need to get the scope precisely polar aligned to fix this. This is a common problem, and one I have to deal with everytime I setup. What is happenning is that the arc that the scope is moving is not the same arc as the sky is moving. So even though your star is staying put the sky is rotating every so slighly around it.
a good explanation of polar alignment and how to do it accurately is here http://members.aol.com/ccdastro/drift-align.htm
Once you get that sorted you'll be away. Hope this helps.
31-08-2005, 02:35 PM
Thanks Robby...makes sence.
I may get Paul to show us how he drift aligns using K3CCDTOOLS.
31-08-2005, 03:15 PM
Good image Tony, and interesting about Guide dog. I spent lots of nights getting my polar alignment just right. And it is still not 100%. You might also consider the flexure you will get from your guide scope. All guide scopes get flexure even if it is a little bit. However, Robby seems to have hit the nail on the head. I have managed to get guidedog to guide well for over 10 minutes. You need good polar alignment to do this. So go back and have a good look.
Your images are very good by the way. When you get this sorted you will be getting even better images.
31-08-2005, 03:58 PM
I have had Guidedog guiding all night even with a small error in polar alignment
and field rotation is apparent if you compare the first image with the last in a series of the same object.The trick is to lower the aggressiveness of the correction (even when all parameters are correctly entered) so you sneak up on the desired position rather than continually overshooting.Hope this helps!
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