CRACKED IT!!!

[Dave_D]

I think...

So after much hair pulling and leaping about i think i finally worked out what was causing my guiding to produce eggy stars. I changed the rings a while ago to skywatcher rings and used the dovetail i got with my autoguider, which was 'quite long'. Anyway, i figured out that having the rings at the very ends of the dovetail was alloing the dovetail to flex ever so slightly. Earlier, i moved the rings closer together (about 10 inches apart) and the whole thing seems a lot more rigid. This is one of the 120s subs im currently doing:

every sub so far has round stars and PHD is reporting an RMS of less than 0.1 

you could say i'm as happy as a pig in s***, and i think i like my setup again.

[Dave_D]

a PHD trace almost flat enough to break the land speed record on 

[wxsatuser]

Well done on finding the problem.

[ollypenrice]

I'd have been sceptical had you asked if this were likely to be the cause of the problem but it looks as if you'd have been right.

Really you're better off with the Losmandy dovetail but if it works...

Olly

[Dave_D]

I'd have been sceptical had you asked if this were likely to be the cause of the problem but it looks as if you'd have been right.

Really you're better off with the Losmandy dovetail but if it works...

Olly

probably true... now i'm back in work, a new mount that's more suitable for what i want to achieve is first on the list. most likely going for an AZ EQ6-GT but i really like the look of those iOptron CEM60's

[laser_jock99]

I believe that inadequate dovetails are the cause of many problems. Longer dovetails will help supporting the scope tube if you suspect this is causing collimation shift issues though.

The real solution is probably longer, thicker Losmandy bars top & bottom . Put more of the load into the bars and less into the tube.

[ollypenrice]

Yes, top and bottom every time if in any doubt.

Olly

[Dave_D]

I believe that inadequate dovetails are the cause of many problems. Longer dovetails will help supporting the scope tube if you suspect this is causing collimation shift issues though.

The real solution is probably longer, thicker Losmandy bars top & bottom . Put more of the load into the bars and less into the tube.

the dovetail is 14" between max centres. the problem i think, is that the vixen gp saddle is a single point of contact and the ota was causing the dovetail to flex by a tiny amount. i dropped the distance between the rings to 8" to reduce the bending moment which seems to have helped up to a point, but the odd thing, is that even though i was getting very good guiding while imaging bodes, i slewed to M92 (after i posted those 2 pics) but PHD seemed to be hunting back and to on the RA axis but practically no correction on dec. i did a drift check and there was no problem with polar alignment.

unfortunately, i'm stuck with skywatcher style dovetails until i can afford a new mount :/

[swag72]

Glad that you got to the bottom of it - It's a satisfying feeling!

[Dave_D]

Glad that you got to the bottom of it - It's a satisfying feeling!

well, 'nearly' got to the bottom of it, but at least i'm getting good guiding more often than not

[skybadger]

With your equipment your not stuck with it. Take off the head of your GP and fit a losmandy adapter to fit losmandy style dovetails.

I'm sure you could drill an altair one to fit. My GP only has two bolts to hold the 'puck' on.

Mike

[Dave_D]

With your equipment your not stuck with it. Take off the head of your GP and fit a losmandy adapter to fit losmandy style dovetails.

I'm sure you could drill an altair one to fit. My GP only has two bolts to hold the 'puck' on.

Mike

Ahh if only... a new mount is my priority as far as astro stuff goes but it has to sit behind:

Finding a new place to live

A car

Essentials for in the new place to live...

I'll get there eventually