[MGTechDVP (Mariusz)]

Hi all.

Seems like it has been ages since I had another imaging attempt or visited IIS. Here are a few images I managed to squeeze out in the last few sessions.

I did my first imaging session using narrow band, namely the Hydrogen-alpha filter on the Helix nebula.
The helix is a combination of 4 seperate nights of sub gathering using both DSLRs, modded and unmodded.

Total Exposure
250min Ha 4hr 10 min
170min RGB 2hr 50 min

RGB 12-08-2013 300D ISO200
Ha 19-08-2013 300D ISO800
RGB 24/25-08-2013 7D ISO500
Ha 25/26-08-2013 300D ISO800

RA Drift was slightly visible in all subs.

5 min Subs were not too bad, 10 min subs were unusable. (more on that and help needed below)

I used the 10 min RA trailed subs only for RGB data.
I used Ha 5 mins subs for Luminosity.

I did hit a snag that I'm hoping to iron out in the next couple of sessions and was wondering if anyone can shed a bit of light on my dilema.

I go through the polar aligning using the 7D, I target the scope on a star in the meridian, while the shutter is open, move the scope on the RA axis for about a minute and ultimately after tweaking leave it for about 10 minutes, move it back for a minute and the star ends up in the same spot. I did this for both the meridian and the eastern horizon to adjust the azimuth and altitude. At both axis the star returns back to its original spot on the DSLR, thinking that the mount must be quite closely polar aligned.

When I set up and start the autoguiding procedure for long exposure, its OK for about 5 minutes, but a 10 minute exposure looked like it was trailing in the RA axis. The guide star is never lost, it stays in the same spot on NexGuide attached to the 80mm guidescope. I thought that either the RA gears are too slow or fast compared to the actual rotation or earth but then that wouldn't make sense for the guide star to stay in the center through out the whole exposure. I considered flexture, so I made sure that the guide scope was VERY securely fastenend in its rings, but there was no difference.

The "RA" trailing seems to get worse as the night goes on trying to gather the subs.
I ended up stacking all of the subs captured with out aligning the stars to see the full trailing over about 2 hours and they show up as arcs. (Shown in the last attached pic.)

My question is, is it possible that this is caused by polar mis-alignment and my drift aligning method is not as accurate as I thought, resulting in a main scope rotation effect around the guide star locked scope. I played with guiding rate & RA/DEC backlash settings in the CGEM settings and I had rates set that made the problem worse, due to agressiveness of the corrections, but no improvement when altering the numbers the other way.

Help please.

Mariusz