A common advice with astrophotography is the most important component in the imaging setup is the mount.
Not all mounts are the same of course.
There is a site where the periodic errror of different mounts is shown in graph form. A really excellent mount does under 5 arc seconds. These would only be a few brands.
Takahashi, Paramount, Astrophysics, Micron, Mountain Instruments, Losmandy Titan. I am sure there a few others.
But of course that all comes with a price tag. Its not so much the periodic error it is the rough sudden jerks that can cause problems. So it is also the smoothness of the errors.
I have a Tak NJP mount and you can get software that will log the periodic errors as a graph after autoguiding. I have seen graphs as low as 1.95 arc seconds with my NJP. That was better than usual. 3-5 arc seconds is common.
CG5, EQ6 etc are probably more in the range of 20 arc seconds or more.
A fork mounted scope is often 30 or more. They also can vary.
Autoguiding has lots of tricks. I often do not get the same guiding errors night after night. Seeing plays a part as well. Focus, balance, focal length of the guide scope, flexure, focal length of the imaging scope, even your choice of guide star and choice of guide camera, choice of guiding software all play a part. Settings in the software, how well you callibrated yadda yadda yadda. So its get complicated really quickly.
But as said, smaller focal lengths are easier than longer focal lengths.
For my setup I have always gotten the best results with the shortest guide exposure I could get. 1 second guide exposures work the best for me unless it is poor seeing where I see better guiding at 2 or 3 seconds. You can also stay with 1 second and set the minimum move to a higher value so not every correction is made unless it is significant.
Getting a 1 second guide exposure is another story. Sbig cameras have internal self guiding which is a great feature but not of much use if you want to do narrowband imaging as you are guiding through the filter.
Greg.
Quote:
Originally Posted by Alchemy
a couple of things come to mind
1. a larger mount might help, find out what the load capacity of the cg5 is , usually for astrophotography its better to be on the safer side, what will pass for visual may not for imaging.
2. try using a focal reducer
3. most mounts are no good without guiding, you might get away with a paramount but not many can do it
4. the guiding is for compensating the periodic error
5. there are methods for imaging the periodic error, phd can also log the corrections which will give you an idea of what is happening
6. Maximum exposure time varies with mount and scope, a longer focal length shows more error and is less forgiving, a higher quality mount has less error. its a bit vague i know but you could aim for 3 min exposures for globs and 5 plus for other stuff.
7.ive noticed on this forum most beginners start imaging with an ed80 and then move up from there, long focal length is challenging i do 1500mm and generally cant go past 6 min subs. theres ways to do longer but most solutions come with a price tag.
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