[g__day (Matthew)]

Apologies if this should be in tips / how to's versus equipment set-up!

Bascially I diagonised the degree of RA trails I was seeing in my longer duration guided shots and determined my image shift is 1 arc second a minute. It may not sound like alot but this means stars have visible trails on 10 - 20 minute shots.

After asking what is the likely source of this error (and thinking it was seeing) Ron Wodaski posted to me on his Yahoo group that is was far more likely that it's differential flexure causing this problem for me...

So basically as my scopes which are mounted on Losmandy side saddle bars move across the sky, the mirrors in the SCT might be moving or the MAK might be shifting against its metal plastic Delphin pins by an amazing 0.0079 of an inch!

I am going to really try and tighten all the gear holding my MAK guide scope to see if that helps, but if it doesn't then its plan B.

I ponder has anyone had success autoguiding using an off axis guider on their main OTA into a CCD like a Meade DSI?

Can you share your thoughts on how this might work and secondly how you bring the DSI into focus? Is there a focal adjustment bar for the off axis focuser?

Many thanks,

Matt

PS

If this all fails then eventually I guess plan C is I go with Robin Cassidy saddle plate or plan D the S-BIG route of guider in built into the main imaging chips light train!

PPS

Don at BinTel just suggested really nail balance - if balance is even slightly out - then this too can cause differential flexure! So that gives me two very free things to try. Step one - check balance on a plank with two ball bearings mounted on it, especially for a side saddle rig. Step two - tighten everything so nothing even remotely appears loose!