UPDATE Sept. 14, 2021:

It seems my DEC problems are caused by Differential Flexure.

The guide scope or lens are drifting during the session relative to each other (in a range that is mostly not noticeable by eye). The reason can be various: pulling cables, insufficient attachment of components…

So I’ve ordered rings also for my guidescope and I’ll attach the lense and guidescope on a parallel dovetail adapter like this one: https://www.teleskop-express.de/shop/product_info.php/info/p223

I’m not sure at the moment, if Differential Flexure is really causing my problems that much. Why I didn’t had this problem already on the Star Adventurer? I still use the same lense, DSLR and guidescope…

More questions than answers at the moment… πŸ™


Just a few words as introduction: I’m writing this post with a bit of frustration. I still have constantly bad results with my GEM28.

Previously I used the Star Adventurer L-bracket with my Canon EOS 70D, EF 400mm f/5.6L and the 50mm guide scope. Also the Star Adventurer 1kg counter weight was attached, to reach at least some balance. It was pretty unbalanced, but I reached 70-90% good results. The RA curves were much better than with the new setup.

A few days ago I recorded again with the new setup a few 12 minutes exposures to monitor once again the performance of my GEM28.

Surprisingly, the performance generally has deteriorated since I use this new ring/doveplate solution, altough its perfect balanced now. Especially RA performs very bad now. DEC always performed bad!

The Recordings

I have absolutely no idea what the DEC axis is doing all the time… it looks terrible!

MGEN Settings

Guider Setup:
162mm focal length, RA guiding speed 0.50x,
DEC 0.50x (same on GEM28)

Guiding:
Gain 9, Exp. 1000, Threshold 10

RA:
Num 1, Tol. 0.20, Aggr. 70%, Mode 2

DEC:
Num 1, Tol. 0.20, Aggr. 50%, Mode 2

Random Displacement:
Uniform Square, 5px

That night I reached 97% orthogonality during calibration.

Really, I don’t know what to do now, since I tried many different MGEN parameter combinations and also adjusted the worm gear meshing to various positions. No success at all.

RA seems to be relatively constant on the curves, but the RA std. values are too high. They are all above the tolerance, configured on MGEN (0.20). At least this value was much better with the unbalanced Star Adventurer L-bracket, attached to the GEM28.

DEC is struggling from the very beginning πŸ™

To be honest, I get the best result without DEC guiding. Otherwise I got DEC trails on 10-30% of the taken exposures.

I recently found a YouTube video (https://www.youtube.com/watch?v=dqGZEtjeOL0), showing the adjustment of the gear meshing on a GEM28. I adjusted mine the same way now and looking forward for clear sky to test and record it.

I have not given up yet!

Besides that all, I like the haptic and the look πŸ˜‰

Share this:

Leave a Reply

*