Image Inspection using Short Subs

[Martin Dowd]

The last 2 nights Ive been imaging M7 Ptolemy Cluster using short 20 sec subs due to my heavy light pollluted skies +B8 whilst imaging a star cluster and found using the Image Inspection tool to be frustrating in respect to finding the true tilt of my imaging system. Some readings were 5% and a few subs later the readings were 12% and then back to 10% and then 17% and so on .....
It wasnt until later I realised that checking Tilt values of endless short subs is fruitless as seeing and sampling is inefficient.
I found stacking say 20 to 40 subs into a master stack gave a much better result at it averaged out the recorded data to provide a more real evaluation.
Another problem I was confronted with is that I use a TS Optics GPU 4 element Coma Corrector in my Newtonians which when using short 20 sec subs can distort small faint stars in the corners of my image frame due to the same issues as the Tilt issue above.
Im now adopting a random visual inspection of individual frames when using short 20 sec subs instead of totally relying on the Image Inspection tool.

Clear Skies
Martin

[Martin Dowd]

M7 Ptolemy's Cluster
Bortle 8 City Skies
Mew Moon
8" f5 Carbon Newt ( self built )
ZWO2600MM LRGB
20 sec subs 4.5 hrs integration
Full Calibration Suite
Reviewed , Stacking and Alignment ASTAP
Post processed in Startools

[han.k]

Hi Martin,

A 10 second exposure should normally be sufficient for a repeatable inspection result but light pollution and very oval stars does not help. A star rich area will also help.

An other thing you could do is first bin 2x2 the image. See tools, bin or stretch. This will improve the star detection and then apply F4 for inspection

You could hit the F6 button to display the center and corners in one image for visual inspection.

cs, Han

[Martin Dowd]

Hi Han,
Thanks for those suggestions
I did discard quite a few subs in this project but the final image turned out ok in the end

CS
Martin