That syncing feeling

[Demonperformer]

Just wondering if this is normal ...

Last night, having aligned the SLT, I slewed to M81/M82 to take some images. I framed them in preview and decided to do a SYNC as someone said this would help prevent drift. Well, it told me I had 'synced to M81', but the image still drifted slowly across the screen (presumably due to anomolies in my initial alignment). Not enough to show trailing (due to short exposure length), but enough that after 40 minutes I needed to do something about it. So I did a 'GOTO M81' and sure enough it moved back into the centre of the screen.

None of the above was what particularly puzzled me.

At this point, however, M81 remained in the centre of the reticle crosshairs for the next two hours. Spot on. I don't really know enough about the SYNC feature to make sense of this.

So my question is this: When you do a SYNC, are you supposed to do a GOTO to get it to work, or is this just one of those freak events for which I should be grateful that it happened, but should not expect every time?

Thanks.

[daz]

Just nod a thanks to your favourite astro deity and move on!!

It supposed to just "do it" - you shouldn't need to goto after the sync

[WayBig]

It's odd that celestron don't seem to mention the sync command in their manual!

I don't think it affects the tracking of the scope, so if your scope is tracking badly for a particular reason (this happens with me if I dont have the scope level or if I knock the scope during or after alignment) sync wont fix that

I think it helps by correcting any small errors in where the scope thinks objects are, so after by goto-ing (is that a word) an object, then performing a sync to it by selecting sync then ensuring that it's centred in the rdf and then the viewfinder you're telling the scope exactly where that object is.

Then if you goto objects in the vicinity of that object the scope is supposed to accurately work out the offset from the object you synced to and find it with a higher degree of accuracy.

For example on saturday night I synced lyra before looking for the ring nebula

I also find it useful if i want to find something that's a long way away from my alignment stars

Thats the way I think it works!

[great_bear]

Then if you goto objects in the vicinity of that object the scope is supposed to accurately work out the offset from the object you synced to and find it with a higher degree of accuracy.

For example on saturday night I synced lyra before looking for the ring nebula

I also find it useful if i want to find something that's a long way away from my alignment stars

Thats the way I think it works!

Can't speak about Celestron, but that's certainly what SYNC is for when using EQMOD/ASCOM. With EQMOD it does nothing to improve overall accuracy, it simply creates a new 3-star zone in conjunction with a couple of other stars that you've already aligned.

In other words, when you ask to GoTo an object, it looks first to see if it lies within any type of triangle formed by any three existing stars you've previously aligned. If not, then it does some kind of extrapolation to get there - which may be wildly out in some circumstances.

Anyway - to go back to your original point - it sounds like you didn't have tracking turned on initially - but go-to forces tracking to be switched on.