Go to GEM28 – Latest Update Part III

Update Sept. 25, 2021

After analysis of the guided material, at least one positive thing resulted: I never reached that good eccentricity values before. This is very sursprising because the MGEN values doesn’t look very well, once again…

FWHM / Eccentricity

The best sub exposures are IMG_1453 and IMG_1455, since they have also the lowest FWHM values. Lower than the first two exposures IMG_1464 and IMG_1465 listed in the SubframeSelector measurements table. This can also be confirmed visually:

MGEN Settings and Results

RA/DEC guide speed 0.90x
RA NUM 1, Tol. 0.1, Aggr. 70%, Mode 2
DEC NUM 5, Tol. 0.1, Aggr. 70%, Mode 2

The results are similar for every exposure, so the screenshot shows only 2 of them.

Gear Mesh

Before this test, I adjusted the gear mesh as follows:

RA: -3/4 turn (from zero play position)
DEC: -3/4 turn (from zero play position)

RA was originally turned -3/8, what seemed to be to tight, but -3/4 is way to much.

I’ll go back to -1/2 turn from zero play position.

My last unguided test was very short and I stopped after one or two 90 seconds exposures, because the Periodic Error was already noticable. Sursprisingly I can exposure much longer as expected (unguided).

Regardless of my DEC guiding problems, this test confirms that my GEM28 performs well unguided, even if the Periodic Error frequently appears on the exposures. But thats normal (internal PE correction is disabled).

My Polar Alignment was not very well that night (visible on the diagonal star trails on the 180s exposure)… Later I did also some guided shots. Now the problems started again… It seems my GEM28 and my MGEN aren’t friends 😉

Guiding Problems

After some guided exposures there were massive RA trails again and the GEM didn’t respond anymore, neither to the MGEN nor to handcontroller commands.

But this time I first powered off the MGEN. Immediately I was able to control the GEM by handcontroller again.

Maybe there’s something wrong with the MGEN connection… Today I’ve ordered a new RJ12 (1:1 pins) cable to replace my 6 years old ST4 cable.

The “DEC guiding adventure” continues…

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