Tracking problems on M42

[5ash]

I have a tracking problem with my LX 90 that results in erratic star trailing . On one photo they trail one way and another of the same object taken a few minutes later trail another way .In an attempt to resolve the issue I tried a 3 minute exposure on M42 and obtained right angle star trails( see attached pic). The telescope is in an observatory on a pier and not subject to wind or vibration. Has anyone any ideas?? I have the telescope balanced and am using a canon 350D.
philip

[JohnG]

Hi 5ash

A couple of questions. How is the telescope mounted, alt-az or polar. If it is polar, has it been drift aliagned, imaging at 2000mm focal length is extremely hard on aliagnment, the slightest mis-aliagnment will show. Did the scope cross the meridian, all SCT's have some mirror flop, that could account for the right angle streaks, from the little sqiggles there could also be a problem with PE. Just a few thoughts.

JohnG

[tornado33]

Yes polar alingment is critical. I thought I had mine down pat but was still getting tiny drift errors that show up when star images are magnified heavily, they are elongated not round, turned out to be the altitude was slightly too high, I will re check it next clear nightwith some more drift alingment. I guess seeing no dec drift over at least 5 mins should do.
Scott

[acropolite]

Might be mirror flop Philip, or maybe rubber banding, are you using guiding. It's worth visiting Pete's astronomy site as he seems to have all the answers. http://www.users.bigpond.com/lansma/Default.htm I haven't even tried my wedge yet and don't intend to until I get a shoestring adapter.

[[1ponders]]

That's a strange looking one Phillip. To me it seems as though initially it was tracking well, then suddenly there was a jump and then the tracking went to pot. Could well be Mirror flop. What is your guidescope and how heavy is it?