Some galaxies from last night

[RobertI]

Had a decent session last night, seeing was not particularly good and I discovered at the end of the session that my drawtube had been drooping (no jokes please:)) because I loosened the wrong bolt on the focusser, hence some slight coma has appeared. The captures are also a bit noisier than usual, which I attribute to using the same darks for the whole three hour session (perhaps someone can confirm this is the likely reason?).

Anyway first up is NGC3718 & 3729 in Ursa Major plus a nice little group of 4 galaxies to the top right. I am not too familiar with the ARP and Hickson catalogues but I believe NGC3718 is also listed as peculiar galaxy ARP214 and I believe the small group is Hickson 56. All galaxies wondefully framed and a lovely sight:

Next up is NGC2841 which has a nice spiral structure which I didn't manage to bring out very well, but there is a nice cluster of galaxies to the bottom right and a number faint galaxies to the top left.

NGC2336 in Camelopardalis has a delicate spider like structure. PGC213387 lies just to the right at mag 17.5. I feel I could have got much more detail of the beautiful spiral with better seeing - one to try again on a better night.

Finally M51 which was incredibly bright, the faint 'nebulosity' which appears to surround its satellite NGC5195 can be seen.

Hope you enjoyed.

 

 

 

Edited February 3, 2016 by RobertI

[Ken82]

Nice images Robert thanks for posting

[Astrojedi]

Fantastic captures... yes the noise in the images is very likely from stale darks. I have seen exactly the same in my images on multiple occasions especially on evenings when the temperature drops more than 5-10 deg C.

[Paul81]

Nice galaxy observing session!

I find that sum stack mode works well for galaxies, and I often use X^0.25 stretch. Between the two of them it can help to bring out the fainter parts of spiral arms. Often though, I'll play with the black / white levels to look at the detail in the faint arms, but burn the core out, and then re-adjust to get more of a view of the core. Thats when the video export will be nice so we can post animated views of what we observed. Working on that feature though after binning...

[RobertI]

7 minutes ago, Astrojedi said:

Fantastic captures... yes the noise in the images is very likely from stale darks. I have seen exactly the same in my images on multiple occasions especially on evenings when the temperature drops more than 5-10 deg C.

Thanks for confirming that Hiten, I must not be so lazy with the darks.....a motorised filter wheel will help.

[RobertI]

2 minutes ago, Paul81 said:

Nice galaxy observing session!

I find that sum stack mode works well for galaxies, and I often use X^0.25 stretch. Between the two of them it can help to bring out the fainter parts of spiral arms. Often though, I'll play with the black / white levels to look at the detail in the faint arms, but burn the core out, and then re-adjust to get more of a view of the core. Thats when the video export will be nice so we can post animated views of what we observed. Working on that feature though after binning...

Thanks Paul, I'll give sum stack a go. I did try the X^0.25 stretch on M51 and NGC2841 and it did enhance certain details, but looked a bit too odd to share! I spent ages adjusting the b/w levels and again more detail was visible at the expense of noise and aesthetics - the video feature will be fantastic and I think will really help us to better share our experiences.

[Chris]

Lovely captures Rob  Yes, seeing was a bit rubbish around our neck of the woods last night, I couldn't get much detail out of Jupiter when observing thats for sure.

[Martin Meredith]

Great captures Rob. NGC 2336 is a real beauty, one I must add to the list.

Some of the noise (not I see much noise in these) might also be due to using median stacking?

Are all these with linear stretch? Even more impressive if so. I barely use linear these days and am just about starting to appreciate the difference between x^0.25 and arcsinh in some images. Those modes do take some controlling though and there is a definite sweet spot (or perhaps more like a hotspot where the effective is at its greatest).

Martin

[RobertI]

Thanks Martin. Yes, I used the liner stretch, I have tried the no-linear stretch on some objects with very high dynamic range and it worked well but I have struggled a bit using it with galaxies like those above, I certainly haven't been able to obtain results as smooth and pleasing as yours. Perhaps next time I shall try posting a linear and non-linear version of the same object to see what people think. When Paul implements video we will all be able to see each other's 'workflow' for adjusting which will be handy.

Regarding Median stacking, I must confess I haven't really taken the time to understand the differences, particularly between Median and Mean, and I must do so. I have previously used Mean so not sure why I switched to Median in the above captures. During last night's session I started with Median but switched to Mean and got more pleasing results so will probably favour that. Sum stacking seems allow slightly more detail but at the expense of increased noise (does that seem right?) and I'm not sure I like the result.

Hopefully at some point I will have more time to understand test the different variants. 

Rob