Processing M45 help

[lalou]

Newbie here. I need your help in trying to bring out the nebulosity from my M45 image. To give you a background, this image is a stack of 54x2mins exposures with 43 dark frames. This was taken in our neighborhood with quite a bit of light pollution. I already stacked it in DSS and removed the gradient (using GradientXTerminator) and tried to adjust the levels and curves and all I got was this. Hope you guys can help me on this one. 

P.S. I also attached the RAW stacked file just in case you need it as well. 

Thanks!  

Autosave004.zip

[MarsG76]

How much light pollution?? was the moon out? how was the transparency when you imaged this?

 You might find that if there is too much LP, it might be too much for the faint nebulosity to punch through... typically 2 minute subs should bring out, at the very least, some of the nebulosity. 

[lalou]

Hi MarsG76. Actually the Moon about to set when I took my exposures and from what I have observed I think the transparency is ok as well. So the Moon was already on the West and Pleiades was just rising from the East during this time. 

I also used a UHC filter to maybe "lessen" the LP. Not sure if that was effective though. 

[alacant]

Hi. Nice shot. I had a quick go using The Gimp in big hammer mode (!). The main problem is the gradient and the vignetting; use flats to cure the latter. Unless you have sodium and mercury light pollution, it's probably best to lose the filter.

Anyway, there's some nebulosity but don't cut off the histogram dark point after (for this image extensive) stretching. Another set of shots added to what you already have should get you a nice result. HTH.

[carastro]

Yes I agree over the need for flats, you cannot stretch it without that ball of light showing in the middle as in Alacant's picture.  If you don't know what they are they a brief image of the light path normally done using the not to bright daylight sky with some sort of diffuser (a piece of typing paper or a white sheet over the aperture.  (you can also use some sort of even light source at night, but not too bright).  The histogram should be about 1/3 to just under halfway across to be of any use,  Too bright or too dark they won't have any effect on your final image.  They will also remove dust bunnies as well.  You need to take around 15 or so of these flats and enter them into DSS in the relevant folder when loading for stacking.  

Flats should be taken before the camera is removed from the scope or the focus altered (or the dust won't line up), but it might help with the vignetting (darker corners) if the camera is already removed.  

It can be tricky to get flats right, but once mastered it will make a whole lot of difference to your final result and ability to process.

Also I don't know what equipment you have, but is it possible to do longer exposures than 2minutes?

HTH

Carole 

[lalou]

@alacant

Isn't GradientXTerminator enough to remove the gradients and vignetting? Will definitely try taking more shots without the filter. Thanks for your advice! 

@carastro

I just usually take lights and darks. Anyway will definitely try your advice as well. Thanks! 

For my equipment, I am using a Celestron C6N on an OmniXLT CG-4 Mount and I am using a Nikon D5200. I still don't have autoguiding that is why I can't go more than 2 minutes. 

[alacant]

15 minutes ago, lalou said:

Isn't GradientXTerminator enough to remove the gradients and vignetting?

I think that with the flats to even out the gradient, it will do a better job. But hey, these are nice sort of issues to have as you have the basics well under control:)

[carastro]

The trouble with gradient exterminator to rely on that alone it can smooth out your nebulosity as well.  It is best to isolate the Nebula when you use gradient exterminator and only use that on the sky background, so it's nto a substitute for flats.  

flats can take a while to get them right but you will see a big difference once you get them right as you can stretch the images more.  

By the way, what software are you using for post-processing?

I use photoshop some use Pixinsight.  I have tried GIMP but find it not a patch on PS

Carole 

[lalou]

Thanks so much for the tips @alacant

Yup I do isolate the nebula when I am using the GradientXTerminator. Looks like I have to try the flats next time. 

For my software I use DSS for stacking then I use Photoshop for the levels and curves adjustment. I am still thinking about buying PixInsight since it is kinda expensive.