Opinions Sought

[mick pinner]

being new to the whole drift alignment and deep space imaging aspect could l get some opinions on the photo of Centauras A in relation to the star movement, details are LX 200 @ F/6.3 2min exp.
my drift alignment through the scope with 12mm reticle seems to be spot on and the fact that the stars appear as 2 seperate points and not continuous trails leads me to think it may be a slight jump in one of the drives, what do you think?

[h0ughy]

drift is there, any wind?

[h0ughy]

any high cloud at the time?

[h0ughy]

have you undertaken PEC training on the drives yet?

[h0ughy]

oh and one last thing, can you put up a closeup of some stars, the image is inconclusive. if drive error then you will see a zigzag.

[mick pinner]

no x 3 Houghy. what leads me to think it's in the drives is that the movement is in the same direction on both sides of centre and does not seem rotational.

[beren]

I was getting the same thing with my set up .I concluded it was my cameras shutter action {D70} that was causing vibration .Since Ive been controlling the camera from a laptop for some reason the problem has ceased .If you have the Canon 350d which I think has a function that locks the shutter mechanism to lessen vibration it might be worthwhile to trail this and see if it stops the problem

[mick pinner]

l do use a remote cable with mirror lock so l can pretty much exclude this.

[JohnH]

Mick, when I had some images like that is was DEC problems. If your polar alignment is good you can turn off DEC compensation altogether - there is not PEC on DEC. The other thing I found recently is not to balance in Dec too well, you want to keep the gears loaded and driven in one direction only (uphill). Try turning DEC correction off.

[Doug]

Mick, how repeatable is this jump?
I am going to try to put up an image of mine that was taken with a 12" classic LX200-f6.3, polar mounted drift aligned, pec trained etc.etc + DSI-c. It is/was going to be NGC253....4x2mins unguided ie. total of 8mins or 1 worm revolution. It seems in my case to be caused by a bit if junk in the drive because although it is 8 minutely, it sometimes doesn't happen, so I am optimistic that it will not turn out to be a damaged worm. The Scope is housed in a dome....no wind issues. Balance....good enough.

So, are you able to see a repeating pattern or is it random, or what?
best,
Doug

[pluck]

Declination drift and tracking errors are two separte issues, independant of one another. If your camera is oriented square, then it should be pretty easy to tell which is which (e.g. up down or north south trails are drift, left right or east west trails are tracking). A diagonal drift indicates the presence of both. Trying to isolate just one of the two issues will help - as neither are related to one another (ie, PE has nothing to do with polar misalignment etc.).

My advice is tackle polar alignment first. Once you can get a star to remain fixed relative to north/south for several minutes you'e there. Then you can tackle PE / jumping RA drive etc (a much harder task).

Good luck,

Paul

[mick pinner]

thanks Paul, will try and isolate the problem tonight.

[Gama]

I agree its P.E.C.
I had the same issue, 2 seperate images apart, after i done my P.E.C. it disapeared.
Its not drift, wind or shutter, as the exposures are long on both trails. If it was wind or shutter then you would get a line not 2 seperate stars.
Fix your P.E.C., as even alignment would cause a line to show.
Must be pretty bad to get it at f6.3

[pluck]

PE is the single most difficult thing to get rid of IMO. When you think about it, when everything is aligned, tied down, balanced focused and sweet, the last remaining source of error is that darned motorised RA drive (price paid for living on a rotating planet).

I spent years battling with the residual PE in an LX200, and it is still a problem for me using a high end research mount engaged in SNe research (can't use autoguiding in survey work).

PE will usually always show up as 'egg shaped stars' (in the east / west direction) in long exposures. PEC will get rid of some, but not all of the wobble - and sometimes PEC can introduce it's own 'drift over time'. Jumping stars are often likely to be non-PE based (unless you have a really bizarre worm) and could be dirt, damaged worm etc. Wind usually accounts for less frequently observed issues - but if you're constantly imaging under windy conditions it could well be a factor.

The key is to tackle each issue in isolation. Do your best to fine tune your mechanics (worm / gear mesh etc.). Tie that 'scope down, lock down the optics (and focuser) camera etc. Make sure you're aligned with the pole. Once you have removed all of the possible variables, you stand a half decent chance of characterising and then fixing any RA wobble you have left over.

At the end of the day, there will always be some residual wobble. If it's obvious (and ruining your astrophotos) it's time to consider a better mount, or a focal reducer.

Have fun,

Paul

[allan gould]

Looks a lot like mirror shift to me. Earlier LX200 had less than the later GPS models but some were terrible. An idea of the "prone-ness" of your scope to suffer from this is to look at how much image shift you get when re-focussing.