CG-5 GT for astrophotography

[cygnusx1]

With the problems i'm having with star trailing, i was wondering how many of you are using this mount, either std or modified to produce decent prime focus astrophotos?

I still have a couple of things i need to check/do before i give up on this mount, but want to check who else is / is not having issues with imaging.

Thanks folks!

[Whippy]

have a look here: http://tech.groups.yahoo.com/group/Celestron_AS/

Tony..

[peonic]

Kev,

Post up one of your subs for us to take a look at, maybe that'll help in providing you with a better diagnosis!

Oh, and answer your PM's

Cheers,

Chris

[cygnusx1]

have a look here: http://tech.groups.yahoo.com/group/Celestron_AS/

Tony..

Thanks mate, am giving it a squiz.

[cygnusx1]

Kev,

Post up one of your subs for us to take a look at, maybe that'll help in providing you with a better diagnosis!

Oh, and answer your PM's

Cheers,

Chris

Will do shortly Chris.

Very happy with C6-S, v impressed with the visual quality, nice and crisp. :thumbleft:

[cygnusx1]

Most of these were v short exposures, 10-30s +-

[peonic]

Kev,

If I was to hazard a guess, I'd say the bottom shot (M31?) was the 10 second, and the top two were the longer exposures?

Looks to my newbie eyes like your polar alignment is off. Does the CG5-GT have a polar allignment scope? If so, have you alligned the reticule? What steps are you going thru the allign the scope?

If it doesn't have a polar allignment scope, can you get one? If not, I guess you'd have to look into drift allignment - certainly not an insurmountable problem (insur-mount-able, geddit! )

What camera are you using btw?

Cheers,

Chris

[Whippy]

I was going to ask if you had polarscope as they don't come with one as standard.

Quick tip: If you haven't got one, just buy a EQ3/5 one as they're exactly the same thing but cheaper .

Tony..

PS, godawful mount joke Chris...

[cygnusx1]

I have the GT mount - it does have a polar finder which i use.

[peonic]

Hmm.

You're running thru the full polar alignment routine - setting the polar scope to the correct position by rotating the RA axis?

You've alligned the polarscope? (with Polaris centred on the "NCP" mark on the polarscope rather than in the circle, a 180 degree rotation of the RA axis doesn't move Polaris off the cross at all?)

Cheers,

Chris

[Andrew*]

though there looks to be some trailing going on in those photos, in the top two it looks to me like the mount has jerked somehow, because the trails are broken.

Maybe the mount is not stable on the ground and is affected by your movements or the wind. Or maybe there's an issue with backlash or a similar mechanical problem.

From the alignment point of view, have you ensured that the tripod is dead level on the ground?

HTH

Andrew

[cygnusx1]

You've alligned the polarscope? (with Polaris centred on the "NCP" mark on the polarscope rather than in the circle, a 180 degree rotation of the RA axis doesn't move Polaris off the cross at all?)

Cheers,

Chris

Ooops, i think you hit the nail on the head

I do believe i was centering Polaris in the centre instead, had no idea there was a larger circle.

Anyway, i went outside today, and practised alignment again, doing it properly this time

Just waiting for some clears dark skies now, will let you know if their is an improvement in trailing once ive done "proper" aligning

[peonic]

Just to try and give you a better indication of what I was talking about on the 'phone earlier.

Here's a diagram of the markings on the EQ5/6 polarscope - I'd imagine the CG5-GT one should be roughly similar (the polarscope in my Vixen GP was pretty much the same, and this gear is all Synta stuff, after all).

(click to enlarge)

The RA axis is rotated to set the time/date (using the setting circles) - this rotates the reticule inside the polarscope to the correct position. You then use the alt/az controls on the mount to move Polaris into the small 'circle' (the CG5-GT manual should provide you with the exact procedure for this)

Obviously, if the polarscope isn't correctly centred in the mount, precise setting like this becomes impossible - which is where the allignment I mentioned earlier comes in.

I generally tend to polar allign before putting the OTA / Counterweights on the mount - makes the alt/az adjustment a little easier and more accurate - you just have to be damned careful not to nudge the mount when you load it up

Another thing to be aware of is ensure the scope is correctly balanced. The 'bumping' seen in these images could well, as Andrew says, be caused by backlash - or an inconsitency in the worms gears but lets get the easy to fix stuff sorted out, and we'll have another look at some exposures to judge.

Hope that helps,

Chris