NGC 6357

[Jean-Yves]

Hi,

Some breaks in the clouds last night let me get an hour of H-alpha data (Sky90 and ST8) of this nebula in Scorpio, comments, remarks, tips welcome,
http://www.lesbeninger.com/ngc6357ha.html
Cheers

Jean-Yves

[Jake]

Not sure I can offer any tips - it looks great to me!

That is a really interesting looking nebula, and is nicely framed.  Do you know if it is
visible visually?

-Jake

[sc02492]

Jean-Yves, this is an expertly processed image, and an interesting region of sky.  Tracking seems excellent.  Very nice detail in the nebula itself.  I notice a gradient from right to left- this may be real (i.e., nebulosity), but I suspect it isn't.  Flats and/or Russ Croman's Gradient XTerminator tool should take care of this (but be careful to exclude the faint parts of the nebula if you use it).  You might consider moving the black point to the right in order to darken the background a bit, but I really like it as is.

Steve

[Jean-Yves]

Jake, Steve, thank you for your comments:

- I do not think this "baby scorpion" is visible  visually, it is very spread out, may be from a very dark site ?
I can't be sure as nothing much is visible from here, I can't even see the nebulosity in M8 !

- I still have problems with flats, I really should build a lightbox... right now I just illuminate a white screen and take an image of it, with a white "teeshirt" over the scope. I think I get most gradients from my flats. I'll try to get rid of them with ImagePlus, or if it does not work, I'll get Russ Croman's plugin.

Cheers

Jean-Yves

[Ron]

Jean-Yves,

Nice image!

Sure glad you got some breaks in the clouds, I know the feeling.

I don't believe I've ever seen this one?  I think you have made me discover a bug in my star program?   That NGC object doesn't show up in my new SNP .  It shows up in my older version so I'm going to email Starry Night and find out what's  up

Thanks for sharing, and I hope you continue to get some cloud breaks!

Ron

[twilbur]

a.k.a. The Cat's Paw Nebula right?
Beautiful shot Jean-Yves! Looks like your setup is working great!

How do you guide, through the ST8 guide chip or with a separate scope?
I've had trouble using the camera guide chip when shooting through color filters and always assumed that using an HA filter would be nearly impossible.

[Jean-Yves]

Hi , it's just next to the Cat's Paw nebula in fact : I wanted to image that one tonight but clouds are everywhere !

I have not used autoguiding recently, too many clouds passing by and I would loose the guide star too often.
I had to throw quite a few exposures on this shot as they were spoiled by passing clouds, so I settled at imaging 3 minutes shots unguided : the AP600 is amazing in steadiness!
I did a good drift polar alignement once and now align the mount with the polarscope, aiming at ... my neighbour's wall ! I got a few marks on that wall that give me a good enough alignment ...

Thanks for the comments and clear skies

Jean-Yves

Ron : I'll try to get some good ones in the southern skies, test your SNP 

[sc02492]

Jean-Yves, I've tried several different methods for flats.  For me, the one that seems to give the most reproducible results is simple twilight or dawn sky flats, exposed to achieve about 30-50% saturation (saturation as defined by full well capacity (in electrons, e) divided by the gain (in e/ADU).  In your image, there's always the possibility that the gradient you are seeing is from light pollution, in which case flats won't help.  Russ Croman's plug in works quite well.

Steve

[dsnay]

Jean-Yves,

While I really do like this image, I think I agree with Steve in that the background could be a touch darker.

Dave

[Jean-Yves]

Hi guys,

I kind of agree with you as well ... I have done some dark point adjustment and a bit of curves ... What do you think ?
http://www.lesbeninger.com/ngc6357ha.html
Cheers

Jean-Yves

[dsnay]

I think I like it better this way. It's a little hard to recall the first one. It would be easier to tell if the first one were available for a quick comparison.

Dave

[Jean-Yves]

Hi Dave,

I know, I also wanted to compare and then realised that I had been working on the original and had not kept the old one ...

After doing too many transformations, I went back to the original shots and reprocessed most of it to get this ... I did some gradient removal as well, though there still seems to be some !

My mind is on the Cat's paw : almost got it two nights back : a break in the clouds, fifteen minutes to connect everything, 30 minutes on the polar alignment, pointing, focusing ... got a sample at bin 3x3 , looked nice, clouds closed again just then ...

I let the system image the clouds for one hour, just in case there would be an opening, no luck, I got 20 blank shots !

Hopefully soon,

Cheers

Jean-Yves