PN NGC6369 comparison – 10 min vs. 5 min subs

[Dennis]

Hello,

Using NGC6369 as a target, I have been trying to investigate and improve the auto guiding on my Tak EM200 GEM as I haven’t paid too much attention to chasing down some annoying source(s) of star elongation since I acquired the mount.

The difference in the faint tendrils of nebulosity above and below the PN really demonstrates the importance of obtaining better data through longer sub frame exposures; although I think I may have lost some detail due to some auto guiding excursions that I am still trying to track down.

Tak Mewlon 180 at F9.6 using x0.8 Flattener; SBIG ST7E CCD camera for image capture and auto guiding.

Cheers

Dennis

[rogerg]

Dennis,

I have tried similar comparisons myself now and then. Always found it very hard to accurately compare, because processing and viewing makes such a difference. My attempts have been with galaxies and less obvious than yours here with this PN.

There's no doubt your 10min subs one is better. Over sharpened? Unsure, perhaps slightly, but it's not "awfully over sharpened". You've got the object very well defined in that image.

Interesting comparison :thumbsup:

[gbeal]

I agree Dennis, interesting. Why is there a bright "star" upper right in the 5 min shot, and not in the 10?
Gary

[iceman]

very interesting, Dennis.

Were both sets of exposures taken on the same night? Or was the 5 mins one night and 10 mins the next?

To me the 10mins looks obviously better, but has the processing been the same? Was the seeing the same on that night?

[Dennis]

Hi Gary

On the 5 min subs photo, the bright star saturated and began to bloom, so when I shot the 10 min subs some 3 nights later, I jogged the drive to move the star just outside the top of the frame to avoid blooming.


Hi Mike

The 5 min subs were captured on 3rd May and the 10 min subs were captured on 6th May. In terms of processing, the “gross” processing was the same for both images, but then I experimented with different sharpening and star smoothing using the Noel Carboni Action.

I think the seeing was slightly better for the 5 min subs, but there wasn’t much in it. I guess the next experiment is to compare 6x5min with 3x10min stacks to compare the difference over 30 mins, rather than 30 and 60 mins.

Cheers

Dennis

[Dennis]

Hi Roger

Yes – it is a time consuming process to do these comparisons but I am finally investing some time to understand and tune my mount’s auto guiding capability, as using a side-by-side guide scope works okay up to around 1200mm fl but as soon as I get over 1500mm I get star trails on even 3 minute subs.

I removed the guide rings and bolted the WO 66mm guide scope to the mounting plate and it improved the auto guiding and just using the ST7 with dual chips has improved it even further, so it looks like flexure was a key component even though I was using WO dovetail saddles.

Cheers

Dennis