NGC 3718

[Stefan B]

Being not sure if it's worth sharing, but here's my take at NGC 3718 in Ursa major:

It's really a cool looking object but my data is aweful. Lots of different gradients, banding and stuff. Just not an even field. I pushed the gradient aggressiveness and gradient falloff almost to the max. Synthetic bias finally ironed out the field. That may not have been ideal for the galaxy but I think in general the signal remained intact. I also masked out the galaxy for Wipe which I usually don't. In the end IMHO it's an okay result given the problems the data set has.

By the way, I stacked in Siril for the first time by using Scripts. That worked nicely. Usually I use ASTAP. But no matter the parameters the stacks always had a strange pattern of hot pixels repeating over the image. I wasn't able to spot these in the single subs and they remained if the subs were stacked without calibration frames. So it should be a problem of the lights... The problem did not occur with Siril or DSS (but the DSS stack had almost no galaxy in the image...DSS just doesn't work in my hands). Maybe a similar problem with ASTAP like the one @Carles reported a while back? Or just indicative that my data was inferior in that case.

Anyway, next time I will have a look at an easier target

Regards
Stefan

PS. See https://www.astrobin.com/l9ms4t/ for technical details.

[Carles]

Hi Stefan!

I think it is a great result, and specially considering the issues you had! You got pretty good details too, and colours are nice as well

about the ASTAP... yeah, for me it was the hot pixels from dithering that remained in the image. Tried different ways and didn't work, but Siril does a great job stacking.

Lately I calibrate with DSS and then stack in Siril with a no bias/darks/flats script and I am pretty happy with results.

It is strange though, the problem you mention with DSS not showing anything, not even when opening the file in ST ?
Maybe is some sort of setting or black point.

Carles

[Stefan B]

Hi Carles,

It is strange though, the problem you mention with DSS not showing anything, not even when opening the file in ST ?
Maybe is some sort of setting or black point.

You can see the galaxy after the Autodev stretch, but it is much weaker compared to the Siril and ASTAP stacks and the noise is much more prominent. At least with my data DSS is just not as good as ASTAP (and probably Siril, but I only used it once until now).

Regards
Stefan

[Mike in Rancho]

Excellent result! Way too hard on yourself. And a totally cool target. I will have to try to remember this one.

I have been using ASTAP more often now for my final stacking. I'll usually stack in DSS first just to get an idea on what I picked up, as it is just so fast. But even though I am using the ST recommended unmolested settings in both (except for ASTAP's AstroSimple interpolation), the DSS results have more artifacts, color casts, and less sharp detail.

I might need a faster computer though, as ASTAP can churn away for two or three hours when there's a few hundred light subs.

[Stefan B]

Hi Mike,

thanks for your kind words. Your right, DSS is much faster, but the ASTAP results are much better, so the time is worth it IMHO.

A faster computer would be nice, mine is seven years old ... ST would benefit from more power, too

Regards
Stefan