M81 & M82 + some surrounding galaxies.... 2023 edition

[AstroGS]

I have to start with this..... the weather has been absolutely atrocious over the past 3 months. In Northampton where I live, I think we had max 3 or 4 nights of clear-ish night skies. In one of those nights - that I was not planning to do any imaging by the way - I went for the M81/82 galaxies with the 90mm refractor. Seeing conditions were ok but, not good and there was some wind as well.

 

Overall, I managed to acquire 70 subs of 300 secs each + flats, darks and bias frames. Was fighting with guiding issues that night (averaged between 0.9 - 1.3 RMS error), which shows at the edge of the image with elongated stars.

 

Stellamira 90ED + flattener/reducer x0.8

ASI2600MC + 2" L-Pro filter

OAG + 290mm guide scope

Integrated & processed with Pixinsight - drizzled the data (although I did not see any difference from the non-drizzled version).

 

[ollypenrice]

Guiding errors will be consistent across the entire frame. If you have issues only in the corners or other particular parts of the frame, the problem isn't guiding. It might be coma, chip distance, polar alignment, chip tilt...

It's a nice clean image but I'd watch the bright end which is slightly saturated with this stretch. If it isn't saturated at the linear stage it doesn't need to be saturated in the stretch.

Olly

[wimvb]

1 hour ago, AstroGS said:

drizzled the data (although I did not see any difference from the non-drizzled version).

With 3.76 um pixel size and a 430 mm focal length, you need good seeing to benefit from drizzle. The downside is the much larger file size, as well as some loss in snr.

[AstroGS]

37 minutes ago, ollypenrice said:

Guiding errors will be consistent across the entire frame. If you have issues only in the corners or other particular parts of the frame, the problem isn't guiding. It might be coma, chip distance, polar alignment, chip tilt...

It's a nice clean image but I'd watch the bright end which is slightly saturated with this stretch. If it isn't saturated at the linear stage it doesn't need to be saturated in the stretch.

Olly

Thanks for the feedback…. Currently I’m playing around with the Generalised Hyperbolic Stretch and the results are more like a hit & miss case. I will try to go back and play with it again when I get some time.

 

Re the elongated stars you are probably right as, it was the first time that I used ZWO’s OAG + ZWO filter drawer and there might have been some tilt or even backspacing issue. I will keep an eye on this.

[ollypenrice]

35 minutes ago, AstroGS said:

Thanks for the feedback…. Currently I’m playing around with the Generalised Hyperbolic Stretch and the results are more like a hit & miss case. I will try to go back and play with it again when I get some time.

 

Re the elongated stars you are probably right as, it was the first time that I used ZWO’s OAG + ZWO filter drawer and there might have been some tilt or even backspacing issue. I will keep an eye on this.

I never use any ready made stretch. I'll use a simple log stretch in Levels till I get somewhere on the way to a final stretch but, after that, further stretching is hand made to suit the data.

Olly