From: Milton Aupperle <milton@outcastsoft.com>

Date: August 31, 2009 12:02:29 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] M33 and NGC 6946 Galaxies

Hi Alan;

Thanks for the kind words. Your Saturn animation is very very cool too.

As to tracking, the main issue I have been trying to deal with on the HEQ5 is a worm / gear interaction which shifts the mount up to 2 arc seconds on the RA axis. This happens somewhat erratically at 4.7 to 9.4 second intervals, which is coincidentally when each tooth engages / disengages with the worm. So the tooth shift throws the mount forward up to to 2 arc seconds, which Astro IIDC corrects for and then it's already slid back into 0 position, so we wind up with an over correction. And filtering out this with PEC on the mount is basically impossible, as it's very difficult to determine if this is turbulence or if this is gear related on the fly. The only thing I would use PEC for is broad peak to peak correction, but even that isn't "consistent" on this mount (might be +30 arc seconds for one cycle, then 60 on the next and 10 after that).

I worked around the tooth shift issue temporarily by backing off the gear/worm tension which nearly remedies the situation (I'm getting about 1 arc second shifts now, which are barely detectable) However that introduces a loose RA axis so that I have 30 arc seconds of play on it. So touching the mount means it shifts +/- 15 arc seconds, and it takes time for the gears to engage when switching back and forth at > 1x rates.

I'll have to take the mount apart again and see if I can get it tight enough to have no play, but not too tight to cause the gear / worm shift issue. I really dislike the fact that they used a brass gear with a steel worm (especially since they have different coefficients of expansion which is zero fun during +/-40°C temp changes here) and may eventually look into replacing it with something better. The brass "gear" is not a  simple gear at all and it's really a big solid brass tube with rounded teeth on the base, so it likely will be really expensive to replace.

TTYL..

Milton J. Aupperle

On 30-Aug-09, at 8:16 PM, Alan Friedman wrote:

Some excellent! images from your vacation, Milton. I can see the good sky conditions from the nice tight stars. 

thanks for posting them,

Alan

Hi Folks;

Two more images from last week.

Messier 33 - the core area of the big galaxy in triangulum:

http://groups.yahoo.com/group/Astro_IIDC/files/DSO/M33_LRGB2x2_20090825.jpg

and NGC 6946 the FireWorks Galaxy.

http://groups.yahoo.com/group/Astro_IIDC/files/DSO/NGC6946_LRGB2x2_20090825_MJA.jpg

Both shot with the C8, 1149 mm FL, 15 minute Luma, 17 minutes Red, 13 minutes Green and 13 minutes Blue. I only got one R G B frame for each one and 3 Luma for NGC 6946 (stupid satellites!) and 5 Luma for M33. I binned them 2x2 when stacking to improve the brightness.

I likely will re-do M33 later on, as it's a bit noisier than I like.

TTYL..

Milton Aupperle