Barnard's E

[VincentMorris]

Dear All,

Been waiting for a moonless and transparent night to capture this one. After so many rainy nights got a break in the clouds early morning of 7th October.

Dates taken: 7th October 2010
Location: Beckenham, Kent, UK.

Scope: Celestron 8 with Hyperstar 3
Camera: Starlight Xpress SXV-H16
Filters: IDAS LPR
Guiding: Skywatcher ST80 with DFK
Mount: Skywatcher EQ6

Exposure: 300s X 25 subs
Calibrated and Stacked in DSS
Stretched and Noise Reduction in Photoshop CS3

There's a bit of field curvature in the top corners. Not sure that caused it; Collimation? Your comments for improvement are most welcome.

Thanks,
Vincent.

[multiweb]

Nice one Vincent. In my experience it can be a result of the guiding star you pick and slight field rotation (worst if you guide from a star right in the corner of the sensor) or your 'flat' field is not centered on your CCD. You should be able to pick that up by shooting one flat and looking at the illumination. I bet the bright spot would be at 9'0clock on your shot. Hyperstar is tricky to get right. Myself I never get it consistently in the same spot. :P

[VincentMorris]

Thanks Marc.

I think you are right; the trailing at the top corners is due to field rotation as the guide star was inadvertently quite far off.

I tried collimation using CCD Inspector. Managed to get the collimation error under 10 pixels. Any further adjustment kept giving me random variations between 3 and 8 pixels. Even consecutive measurements without touching the collimation screws gave this variation. Effect of seeing?

Thanks,
Vincent.

[Hagar]

Nice image Vincent. Stars are my bug bear as well. We will work it out one day and get nice sharp corners.
Nice.

[multiweb]

If you use CCDIS the results might differ depending on the field you shoot and the orientation of the scope. I find 1mn exposure on a uniform starfield devoid of bright stars or only one bright star in the middle give me the best results.

For the initial alignment I do everything indoors with the ACT from Hotech (http://www.hotechusa.com/category-s/23.htm). Much easier on a bench and you can fiddle to your heart content. CCDIS field to confirm only.

[strongmanmike]

WEll that's an Excellent E VincEnt :D

MikE