Aiming problem...

[Astrobiker]

I've recently been getting to grips with using an LPI on my 10" Meade LX90 (alt/az mount), and I'm getting an infuriating problem with fine tuning the composition of the picture. Having got Jupiter roughly framed, and trying to bring it to the centre, I slew it to position only to watch it drift back to it's original position in about 5 to 10 seconds where quite happily tracks it as steady as a rock:confused:. It doesn't matter how many times I drag it to the centre, it still drifts away to where started. This has happened on numerous occasions and it is getting to the point where I will throw the 'scope over the hedge before long...

I have gone through the routines for calibrating and training sensors and drives, all to no avail, any bright ideas???

I'm managing to get some reasonable results but I could do far better without all this frustration. Attached are some of my images from a complete transit of Io's shadow, I have an animation but I'll have to change the format before I can show it here.

[Milamber]

It's the backlash in the gears... only real options are to either get rid of the backlash... or move the target off centre the other way so it drifts back to the centre instead of away from it.

Arthur

PS - nice pics btw, in fact *excellent* pics!

[The Warthog]

Lovely series of pictures there. I have a similar problem with my RA drive. I find the solution is to make sure the last movement of the drive was in the direction of the sky's motion. If necessary, I give it a little kick just to take up the slack in the gears, and it tracks perfectly. I don't know if that is advice you can transfer to your drive, but if you can...

[brianb]

If the drift is up & down (which it was with my LX90) try weighting one or other end of the tube so that the drive has something to work against. If the planet is east of the meridian, therefore rising, the front of the tube should be heavy; if west of the meridian, the tail of the tube. That way the drive will take up the backlash ... if weighted the other way, the tube will tend to "stick" until the backlash has been taken up, causing the planet to drift.

Same applies in RA / azimuth too if your scope is wedge mounted. If altaz, try loading against the direction of motion with a rubber band / bungee cord.

[Astrobiker]

Thanks for the advice, I've not had an opportunity to try it out yet but I will keep you posted. In the mean time the transit animation is attached, it's a bit jumpy but it does clearly show the motion of both Io and it's shadow relative to the planet's rotation. I hope for better things in the future.

[The Warthog]

That's very good. You can also see Io herself moving across the planet. :headbang:

[TheThing]

That's cool! All with a LPi too. Brilliant!