alignment stories

Told Manuel about my polar alignment problem last night...

I had set up my mount, motor, 'scope, dew heaters, power supply up and completed an accurate polar alignment using the built-in polar scope (like how I had taught him with his Atlas mount). I even did it with the telescope not mounted (which I normally don't do). But when I viewed Vega, I saw it was drifting.

I double-checked the alignment against the very accurate SkyTools3 software. Still, after a minute or two, I was off target. I did the alignment again and restarted all the electronic equipment. It was better but still drifting. I wondered if I had done something backwards, i.e. had a view off by 180 degrees. It wasn't a low battery; I was on an AC source. I was perplexed but wanted to press on.

Hooked up the SKYnyx video camera and computer and tried to image the Moon. It was drifting fast! Of course, with the long focal length of a SCT, it was pronounced.

I took the camera off and started doing formal drift alignment corrections. I had some minor drifting along the Dec axis; major drifting in RA (hint!). The Dec drifting decreased but didn't go away. Weird.

I actually did another form of drift alignment, a completely different technique, using the setting circles, and it helped some more. Despite using this alternate method I got to a point where any change I made, I could not correct the drift any further.

Something was really strange... Start over. I re-did the polar alignment with the polar scope. Put the camera back on. And tried to image Jupiter. Still drifting.

Then I had a thought... I centred Jupiter in the camera and turned off the dew heaters. The drifting instantly stopped! No drift at all. I had perfect alignment!

It turned out that my dew heaters were drawing too much power from the power source and causing the RA motor to run at an improper speed.

I grabbed one of my lead acid batteries and put the motor on it and the dew heaters back on their own separate supply. Everything worked great for the rest of the night.

Manuel got a kick out of it.

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This also explained something else that I had experienced, but had not crystallised. I kept checking the dew heaters and they did not seem that hot. Even when I had the controller near max. At the time I just chalked it up to it been still fairly warm out... Later, when the dew heaters were on their own... toasty!