Strange star elongation problem

[raymo]

I was ready to start imaging last night, and took a 10sec sub of the Jewel Box for framing purposes, and found the stars very elongated. Intrigued, I took shorter and shorter subs to see when the elongation began to show itself. I got down to 1/60th sec at ISO 6400, and the stars were still elongated. Everything from the tripod to the camera was firmly in place as usual, and of course the shutter was fired remotely. Anyone got any ideas how this could be happening. The R.A. motor was running, and even if it wasn't, I should be able to get round stars for longer than 1/60th sec.
raymo

[jamiep]

Tracking rate set to Solar or Lunar?

[raymo]

Hi Jamie, No, set to sidereal as usual; in any case 1000mm focal length
should allow for around 1/3rd sec with no tracking at all. Even at 1/60th sec they were still well elongated, so I don't think the problem has anything to do with tracking. I wondered if something inside the camera had come loose, but general daytime shots are perfect. We'll see what happens tonight, assuming not too much cloud.
raymo

[gregbradley]

Something not square. Using a reducer at the wrong spacing are 2 possibles.

Mount not tracking at all is another.

Greg.

[raymo]

Thanks for the suggestions Greg. There is nothing in the optical train between the camera and the focuser, but I like the idea of out of square, I'll have a close look at that tonight. Even with no tracking stars should be round at 1/60th sec @ 1000mmm f/l. I can't imagine why anything
should be suddenly out of square as the only fitting is the T-ring to the focuser, but it appears to be the only logical reason for stars to be elongated with such short exposures.
raymo

[rustigsmed]

possibly a bit of camera tilt Raymo? maybe take it out of the focuser and put back in? perhaps the tightening mechanism has loosened a bit?

Russ

[cometcatcher]

Collimation slipped out? Tube currents? I get tube current astigmatism if I don't allow the tube enough time to cool.

[raymo]

Looks like Russel and Greg were right; after ensuring that the camera was square with the focuser the instant star elongation was gone. Having said that I still got elongation starting at 8 seconds. For months I have been having tracking problems, and cracking noises in the R.A. shaft.
[they've stopped]. This time the massive drift is in Declination. How can this be when I got the P.A. down to single figures of seconds? with the P.A. stars inside the centre square of my reticle. The Go To with this mount has been very poor and inconsistent from day one. The target is sometimes outside the F.O.V. of my finder, let alone a low power eyepiece. I have been using EQ mounts for nearly 60 yrs, and imaging for nearly 50, and have never experienced anything like the 2 1/2 yrs since I got this mount. When everything was greatly improved using a borrowed hand controller, I thought I'd found the problem. Got a new V.4 controller; first night all was great; after that all went back to how it was before. Looking through my diary I've done 109 sessions with this mount, and in only 11 of them did everything work as it should. That's 98
forty five minute setup and aligns for absolutely no result.
To cut a long story short, I am now in a state of despair, and am stopping imaging before I go insane.
raymo

[LewisM]

Balanced?

Backlash compensated? - better still, adjust the meshing

I had an issue with an HEQ5 where the peened on spur gear on the motor slipped - got to the point where it failed (the motor simply rotated with NO movement of the spur gear).

QC on the earlier SW mounts was pretty spotty. 1 failed HEQ5, 2 failed NEQ6's for me. Put me off SW mounts a LOT.

[rustigsmed]

hi raymo,
sounds like one problem sorted, making progress.
do you know what firmware you are running on the handset? it should say something like v4.36..

Russ

[raymo]

Version 04.05.17 Russell. I've marked both gears Lewis, no slippage;
anyway my latest problem is with Declination, and the Dec motor is of course not running during imaging. [unless using an autoguider of course]. I adjusted the meshing a couple of months ago. Couldn't eliminate the backlash entirely without getting a tight spot.
Collimation is pretty good Kevin, and the scope had been outside nearly 1.5hrs last night before I tested the tracking, so I wouldn't think it would be tube currents. Balanced with a little bit of weight against the drive. I was going to do the belt mod, but I won't bother now.
Thank you all for your thoughts.
raymo

[rustigsmed]

I would be updating the firmware Raymo, the earlier versions from my understanding have been hit and miss ... its up to V.4.37.03 now!

I've got the "36" version on the v3 handset, from reports in another thread the "37" version is a solid performer.

Russ

http://www.skywatcher.com/downloads.php?cat=50

[raymo]

Thanks Russell, I will update. The 4 hasn't been on the market very long; I wouldn't have thought there would have been so many updates already.
The 4 is a definite step backwards, I wish I could have stayed with the 3.
It doesn't even fit in the plastic holder on the eyepiece tray.
raymo