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.

stargazine_ep29_banner.thumb.jpg.da7f3b163f7bd35187cb558b0346baf6.jpg

Shibby

M42 - managed an image!

Recommended Posts

This is technically my second attempt at a DSO (see here) but since then my breakthrough is that I can use a barlow to move the focus out from the tube and achieve focus without an eyepiece (and the awful coma that comes with it!).

So I'm very chuffed to have achieved this image, I'm delighted with it! :D I stayed out til 3am last night, trying to make the most of the brief clear skies that might not re-occur any time soon!

output2-tweak3-small.jpg

There is still a fair bit of noise. DeepSkyStacker only stacked 3 of my 18 subs - because most of them had star trails (I only have an Alt-Az mount and the FOV is small with the barlow, about 0.6deg I estimate). Is it just random luck that 3 subs tracked perfectly?? I also used 18 darks, no flats or offset. I used nikon Capture NX to do attempt post-processing on the levels, though I'm very new to all this.

I don't think the focus is right either, I didn't have much time to fiddle with it before clouds threatened.

Share this post


Link to post
Share on other sites

Hiya Shibby, that's a great start, much better than my 1st and 2nd attempts. This is not the easiest of targets as the stars soon become over exposed before the nebulosity becomes apparent. Can you provide the sub details? There is some light pollution evident but once you get the hang of processing this can be sorted out. Try focusing on a nearby bright star, a Bhatinov mask makes this a lot easier to achieve, then slew to your target. Once I have good focus I put a mark on the telescopes draw tube for future reference, and then it may just need tweaking.

It's a very long learning curve, but all the help you will require is right here on the forum....

Carl

Share this post


Link to post
Share on other sites

That's a very nice start Shibby.

It's a shame you need a Barlow to get focus outside the drawtube as they introduce spherical aberration as well as reducing the intensity of photons reaching the chip (hence increasing the exposures required by the square of their magnification). Increasing magnification in this way will also exaggerate any tracking errors which would explain the number of subs you lost to trailing. If your alt az mount isn't all that hot, tracking-wise, I would try mounting a DSLR piggyback and see how you get on.

Edited by Dangerous-Dave

Share this post


Link to post
Share on other sites

Thanks for the comments!

knight: oh yes, sorry the subs were all 30s at ISO800, I don't think I can go much longer at this sort of FOV and mount, not unless I want a worse sub success rate than 3/18!

About the light pollution, where do I start trying to process this out? Or is it worth looking into filters? There is a fair bit of light pollution where I am.

I'd like to try a Bhatinov, I might try and make my own out of card...

dave: yes it is a shame about the barlow, I've tried everything else but this seems to be my only workable option... You can't get a 1.5x barlow can you? :D

Share this post


Link to post
Share on other sites

Antares do a 1.5x barlow...not sure of the quality though..

I think using "darks" helps with the light pollution problem..

Get or make a Bhatinov mask,,you won't regret it..

Share this post


Link to post
Share on other sites

I think using "darks" helps with the light pollution problem..

Darks only remove image noise (mostly hot pixels) in the final data, they have no effect on reducing light pollution in any way.

Getting/Making a Bhatinov mask is a great idea.... I now have them for all my scopes.

Share this post


Link to post
Share on other sites

Steve what's the best way of removing light pollution apart from going round the local vicinity with a catapult and bag of ball bearings???

Share this post


Link to post
Share on other sites

If I were to offer two pieces of advice it would go like this.

1/ Don't let the software tell you what to do. You tell it what to do. Look here Astrophotography for combining methods that should not throw away most of your subs.

2/ PS will deal with the level of LP in your picture with ease.

Dennis

Share this post


Link to post
Share on other sites

If using PS just be sure to measure the level of colour in each channel using the Info Palette and then use Curves to modify the bottom (usually) end of each channel's curve to make the background neutral. Anchor the rest of the curve to a straight line. I have just re-arranged the links on my tutorials page and I think they work! Go to the link above and navigate through to the section on Colour Balance.

Dennis

Share this post


Link to post
Share on other sites

A slight reworking of the image. I think I've managed to preserve more detail in the centre of the nebula.

output3.jpg

This is still only 3 subs stacked, so I will have to get out and take some more, hopefully this will reduce the noise in the image? The red colour seems to be noise rather than LP, it only came visible when really stretching the curves. On the original, I used a sneaky noise reduction which made it look like smooth LP. This time I've been a bit more careful with the curves and haven't used any noise reduction.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • 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.