Crisp, Sharp Images

[mcg_photogrpahy]

Hey everyone! I'm having issues with getting crisp detail in my photos even though my focus is perfect (I use a bahtinov mask). I'm hoping it's just my editing skills, but I just want to make sure its not an issue with my aquisistion or something. I'll attach some sample photos to look at. Both photos were taken with the ASI 183mm Pro, 300 second subs at unity gain. The CA nebula is around 16 hours of data while the Rosette is around 12. 

[Budgie1]

I'm not a mono imager but a few questions which may help others who are:

• What filters did you use?
• Did you check the focus on each filter?
• What are the stacked images like for each channel, are they all in focus?
• What post processing software are you using?
• Which scope did you use and was it with a flattener/reducer?

There's nice data in there, hopefully someone with more knowledge than I will be able to help.

[mcg_photogrpahy]

I used the ZWO 7nm narrowbad filters

I always check focus when switching filters

Each channel look like it is in focus, just bloated star in my OIII channel usually 

Photoshop for the Rosette, and Pixinsight for California ( Ijust got the trial)

Zenithstar 61 with the field flat 61A

Thanks for the reply! The only thing I can think of that might mess with my images is the field flattener, sometimes it can get loose and I have to check it occasionally, but if it were messed up during these sessions, my stars would be elongated towards the edges. 

[mcg_photogrpahy]

11 minutes ago, Budgie1 said:

I'm not a mono imager but a few questions which may help others who are:

• What filters did you use?
• Did you check the focus on each filter?
• What are the stacked images like for each channel, are they all in focus?
• What post processing software are you using?
• Which scope did you use and was it with a flattener/reducer?

There's nice data in there, hopefully someone with more knowledge than I will be able to help.

Sorry, forogt to quote you so I'll post again:

I used the ZWO 7nm narrowbad filters

I always check focus when switching filters

Each channel look like it is in focus, just bloated star in my OIII channel usually 

Photoshop for the Rosette, and Pixinsight for California ( Ijust got the trial)

Zenithstar 61 with the field flat 61A

Thanks for the reply! The only thing I can think of that might mess with my images is the field flattener, sometimes it can get loose and I have to check it occasionally, but if it were messed up during these sessions, my stars would be elongated towards the edges. 

[MartinB]

Your camera is nicely matched to your scope which is good for starters.  I assume your guiding is reasonably tight.  Are you using PHD2 and if so, have you looked at your guiding data to check?  Perhaps you could post some ha images which have just had a simple histogram stretch with no other data manipulation.  There is a surprising amount of noise in the California Nebula image which, I am guessing is due to some sharpening.  I am suspecting that your data is fine, it will never look "tack sharp" on account of atmospheric turbulence but an image with no processing other than histogram stretch should confirm this.

[The Lazy Astronomer]

Have you tried deconvolution? That can help recover detail smeared by atmospheric conditions. 

[wimvb]

What are your expectations? Even if you have done everything "by the book", and expect those crip details, it can be atmospheric conditions that limit the level of detail you can achieve. So if your expectations exceed what your skies allow, there really isn't anything you can do during the capture phase to improve.

[JSeaman]

It looks like a good image to me, more data always helps and using Ha as a luminance layer over slightly blurry base layers helps. Below is just a star reduction and removed a bit of vibrance

[vlaiv]

You are oversampled at 1.38"/px with 60mm scope. You want to be at least twice that sampling rate at about 2.76"/px.

Airy disk size in Ha light for 60mm scope is 5.45". Add a bit of seeing and guiding error to that and you end up with star FWHM of almost 4" and in poor seeing even more.

You really want to bin your data x2 while still linear before you start processing to gain some SNR as well.

That is the fact of life - small scopes simply don't have resolving power of larger scopes and are suited to low resolution wide field work. If you put small pixels on them - you get blurry image when zoomed in.

 

[jimjam11]

Your images look good, but they do look oversampled.

1. You could use the PI SubframeSelector process to measure FWHM on all your subs and look for outliers, but also compare them to the theoretical values vlaiv suggested. I use this on every sub I capture and record the values so I know what range to expect from certain combinations (e.g. ASI1600mm + ZS73 gives me typical stars of 3.9" with my seeing)

2. Depending on the output from SubframeSelector you might not actually be in focus. There is a skill in using a b-mask (which I dont posess!) and when I switched from b-mask focussing to autofocus I got smaller stars. Using something like the b-mask tool in Nina can help ensure you are really in focus.

3. If the ZS61 is like the ZS73 it will have a tendency to bloat brighter stars.

[ollypenrice]

Be aware that focus will drift with change in temperature so a regular re-check is a good idea. 

I think your data look OK for a 60mm scope. The image would take more local contrast enhancement, I think, and sharpening. You could post a linear stack for us to find out...

Olly