Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

hjw

NGC6744 - What to do?

Recommended Posts

Hi,

I've been imaging a galaxy (NGC6744) in the constellation of Pavo over the last few nights. The object is rather big (20'x13') but faint (surface brightness 14.79). I started too late on it because I can only get about 1 hour shortly after sunset. So far I've got 2.5 hours of exposure time with 2-4 min at ISO 800 or 1600. The image is still extremely noisy and I can only just make out the outer spiral arms. My question is, how do you improve imaging on very faint targets. Obviously, more exposure time - but seeing the improvements from one night to four, I am not sure it will get me where I want to be. Darker skies later at night would also help but that is not an option until next year. I am just wondering whether there is anything I am missing.

 

1578159993_NGC6744cropped.thumb.jpg.c835a7ee97e230fded819e1da0d5124f.jpg

Equipment: Saxon 200DS on a HEQ5, SW ST80 with ASI120MC for guiding, Pentax K30 with GSO coma corrector, 120-240sec exposures ISO 800 or 1600, 20 flats and 150 bias frames for each ISO.

Thanks!

HJ

  • Like 2

Share this post


Link to post
Share on other sites

No, you haven't missed anything. The only way to improve this image is more time on target. (Oh, and possibly a cooled camera ?).

If you image just after sunset, the sky isn't dark yet and will add a lot of noise. You already know the remedy: dark skies and lots of data. Unfortunately there's no shortcut in AP. Personally, I would move on to another target, higher in the sky, and revisit this under better conditions.

  • Like 2
  • Thanks 1

Share this post


Link to post
Share on other sites
2 hours ago, wimvb said:

No, you haven't missed anything. The only way to improve this image is more time on target. (Oh, and possibly a cooled camera ?).

If you image just after sunset, the sky isn't dark yet and will add a lot of noise. You already know the remedy: dark skies and lots of data. Unfortunately there's no shortcut in AP. Personally, I would move on to another target, higher in the sky, and revisit this under better conditions.

Thanks! I was hoping I missed something and hope dies last... Well, there is always next year.

  • Like 1

Share this post


Link to post
Share on other sites

I've never yet been able to properly image the Orion nebula. At my locations it was either not clearing the trees or above a neighbour's house where the air was unstable. Now that I've moved to a dark location with a clear sky line, I can finally add it to my list.

Share this post


Link to post
Share on other sites

I agree that the only way to improve it is more time, more subs... really no other way without changing locations to a darker site where you can double the exposure time per sub..... It's getting there...

 

  • Thanks 1

Share this post


Link to post
Share on other sites

There is certainly quite a bit of detail coming through there!

The only thing I can add is that the signal-to-noise ratio only increases with the square root of the exposure time. Quadrupling the exposure time would therefore only halve the noise with respect to the peak signal. I spent 7 hours on the Orion Nebula at F/4.8 last winter and still the background detail could be improved, and the Orion nebula has a far higher surface brightness than your target.

M42USM3expcropcurves3.thumb.jpg.a2c6ed3e05a7e8aec8e995b2774e2289.jpg

The core of the nebula is fine, but the faint outlying regions are pretty noisy. I will add a lot more this winter, if the weather allows

  • Thanks 1

Share this post


Link to post
Share on other sites

If you are only able to image for an hour before the target drops below the horizon, then this will be another factor, as you are imaging through a thick bit of atmosphere.

You would be best to wait until it is higher in the sky.

Carole 

  • Like 2
  • Thanks 1

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.