Help - I'm getting eggs and doubles and L's

[JimsShed (Jim)]

Hi all,
I need some opinions or advice on why I'm sometimes getting eggs or doubles or even L shaped smudges in my images. Only noticed this in my last 2 nights. Other times my stars have been round and no worries. Happens whether exposure time is 1min or 2mins. Setup each night was 2 rounds or star and polar alignment, and seemingly spot on using the Synscan polar alignment function.
Weird thing is that I might take say 8 images, and some will be okay, and others distorted. Using an intervalometer, focus lock on, everything tight, no wind, no dogs, no touchy etc.
Only environmental difference to previous sessions was much colder weather.

Setup is a Skywatcher ED80, EQ5 goto mount, Hotech FF, and Sony a6000 DLSR.

Any thoughts?

Jim

[bojan]

Looks like mechanical problem
Backlash in worm gear? Balance? dirt in worm gear? dirt in bearings? something loose?

[Tony_ (Tony)]

Looks very similar to a problem I had. It eventually went away by itself. Like Bojan suggested it might be dirt in the worm gear or bearing and eventually it may be crushed to nothing - I think that's what happened to mine?
Unless you want to pull your mount apart to clean it you could try putting up with it for a while and hope it eventually goes. Is it every sub? Mine was about every 8 subs (x 30secs).
You can check your backlash and bolts/screws etc.

Tony.

[JimsShed (Jim)]

Thanks guys.
I've gone over everything this afternoon and tightened Allen screws etc. Found nothing very loose, but some took a quarter turn.
Also discovered that it's really easy to expose and check the brass cogs (see pic) by removing 2 or 3 phillips screws. In fact the DEC motor has an open hole to the cogs on the underside of the cover if you get underneath and look up so with the grease in there it wouldn't be hard for a bug or bit of grit to get into the gears. I think I'll tape it over.
I wiped out the gears and re-greased.

Yeah problem can be seen on every 5th to 8th image. I was going to give it a test this evening but the clouds have moved in. Hopefully tomorrow.

Jim

[bojan]

It may be periodic.. does it coincide with worm turning rate?

[cometcatcher (Kevin)]

Unbalance the scope a little so the drive has to work a little harder. For example make the scope slightly nose heavy for pointing in the east and slightly tail heavy for western tracking. Most gears have some play and this stops them wobbling about.

[willik (Willik)]

Check your polar Alignment with Drift method to see how accurate you are dont rely on software for Alignment
Willik

[JimsShed (Jim)]

Good news it appears to be fixed
Finally had a clear sky earlier tonight so got out quick and did some imaging. No more eggs or blurs.
Bolt tightening and gear greasing seems to have done the trick. Bonus is that the tracking is now almost silent.
Thanks guys for your advice and ideas.

Jim

[Andy01 (Andy)]

Also, check balance in dec when parked. Unlock the clutch and see if the Ota moves at all. If it does you may need to rotate the focuser. Also cables/lens caps etc can affect balance, which in turn affects tracking and sometimes creates eggs & wobbles. I experienced this with my EQ6 but its all good now.

[sil (Steve)]

balance shift as mount turns, wind, cabling tension, mirror flip vibration in camera, anti vibration feature of camera . 99.9% aligned is not good enough in my experience. is tripod on lawn or paving? how far from traffic?gears using factory grease or better lubed?