Keeping Alnitak under control

[Miguel1983]

Hi,

i'm shooting B33 in Ha right now, and i've just stacked the first 12 4min subs.

What i feared came true, Alnitak is all over the place 😞

Suggestions ?

 

 

[Kinch]

I'd be interested to know too, if anyone has ANY solution. The different brand filters leave one with different effects and the last time I shot this area I had a hard job calming down what my Astronomik filters left me with. Last night I was imaging with an Astrodon Ha filter but with very humid conditions - so more problems to be sorted....part screen shot to show what I mean.

Tonight I am imaging with RGB filters (still humid conditions) and it is no better 🙄.....worse even!

So - I must prepare for lots of time processing.....what fun 😏

[ollypenrice]

15 hours ago, Miguel1983 said:

Hi,

i'm shooting B33 in Ha right now, and i've just stacked the first 12 4min subs.

What i feared came true, Alnitak is all over the place 😞

Suggestions ?

 

 

This is a probably a microlensing artifact for which many of the present CMOS cameras are well known. Alnitak itself is very good and sweetly split.  There is no clean (some would say 'ethical') way to repair this but if you learn Photoshop's arsenal of brushes you can get it to look like this:

You might well prefer the honest artifact, though this was done with just a screen grab and could look better if done with a TIFF. I made a copy layer and initially worked on the bottom, using Curves to get the diamond-shaped artifact flattened out into a uniform brightness. I used the eraser to make a 'hole' in the top layer and then lowered the brightness of the bottom layer till it all looked seamless but very flat. I flattened that and then put a circular selection around Alnitak, feathered the selection and brightened it to give the star a more spreading glow. None of this has anything to do with astronomy, it's all graphics!

15 hours ago, Kinch said:

I'd be interested to know too, if anyone has ANY solution. The different brand filters leave one with different effects and the last time I shot this area I had a hard job calming down what my Astronomik filters left me with. Last night I was imaging with an Astrodon Ha filter but with very humid conditions - so more problems to be sorted....part screen shot to show what I mean.

Tonight I am imaging with RGB filters (still humid conditions) and it is no better 🙄.....worse even!

So - I must prepare for lots of time processing.....what fun 😏

Awe c'mon, that's a good Alnitak and a dead easy cosmetic fix if you felt like doing it. It's a bit blotchy from the cloud but you could shoot more data or just noise reduce the bright area. If you wanted to hold it down you could just make a gentler stretch of the same data and either layer mask it in properly or just paste the gentler stretch underneath and use a feathered eraser to take the top layer off. Proper layer mask tutorial is here: http://www.astropix.com/html/j_digit/laymask.html Jerry Lodigruss is very good and a nice guy! Here he uses different exposures but it will work with different stretches as well.

Olly

[Kinch]

Thanks for the comments Olly. I have been spoilt in not having to deal with Alnitak for some years - it now stands out like a sore thumb to me. It looks much worse (to me anyway) at the higher resolution on my screen.....and not something I am used to dealing with. With that in mind, your pointers & link are very welcome....I don't think more data will be an option anytime soon.  Thanks again 👍 

[Miguel1983]

Thanks Olly,

i think you're right on the money, microlensing is what a friend told me too and indeed, one can only try and do some touch ups in PS.

Must say i didn't pick my targets well since i got the ASI1600, did IC443 and M45, both had the same artifact, guess i should stay clear of bright stars or learn to live with it.

[david_taurus83]

Try turning the filter around. Its definitely dependent on the type of scope, flattener, filter, spacing etc. I could shoot 15 minute subs of this with my William Optics GT71 and I got a barely noticeable effect, though a much bigger star. In fact, it may actually have been the longer exposures that swamped the detail of the microlensing so you could try that also.

[bdlbug]

Agree with David, my recent experience with imaging B33 with Baader Ha (7nm)  The marked difference in two sessions with Alnitak halo and ASI1600 microlensing definitely demonstrates a dependence on accurate focus, spacing between FF/FR and the orientation of the filter. I got improved results by accident as I had worked out I needed to reduce the Riccardi F/R back focus spacing by about 1-2mm into to eliminate some elongation in stars at corner of images, however when I re-assembled the optical train I put the filter wheel on 'backwards' and the difference is below. There is still microlensing in both images, that can be cosmetically improved in PS, as per Olly's comment above, but the large Halo which is very difficult to remove in any post processing is significantly reduced.  So I would definitely suggest to OP, @Miguel1983 , if it is possible  to reverse the orientation of EFW and re-run a Ha session on B33 and compare.

I am using a AT106EDT, Triplet APO

Before modifying back focus and initial Filter wheel orientation

After changing FF/FR spacing and reversing filter wheel orientation

 

Bryan

[Miguel1983]

6 hours ago, bdlbug said:

Agree with David, my recent experience with imaging B33 with Baader Ha (7nm)  The marked difference in two sessions with Alnitak halo and ASI1600 microlensing definitely demonstrates a dependence on accurate focus, spacing between FF/FR and the orientation of the filter. I got improved results by accident as I had worked out I needed to reduce the Riccardi F/R back focus spacing by about 1-2mm into to eliminate some elongation in stars at corner of images, however when I re-assembled the optical train I put the filter wheel on 'backwards' and the difference is below. There is still microlensing in both images, that can be cosmetically improved in PS, as per Olly's comment above, but the large Halo which is very difficult to remove in any post processing is significantly reduced.  So I would definitely suggest to OP, @Miguel1983 , if it is possible  to reverse the orientation of EFW and re-run a Ha session on B33 and compare.

I am using a AT106EDT, Triplet APO

Before modifying back focus and initial Filter wheel orientation

After changing FF/FR spacing and reversing filter wheel orientation

Bryan

Hi,

i can see the difference, but i'm not sure witch i would like "better", after you rotated the EFW is seems like there's a pinched line instead, also didn't that give you more vignetting ?

Thanks for sharing your experience

[ollypenrice]

3 hours ago, Miguel1983 said:

Hi,

i can see the difference, but i'm not sure witch i would like "better", after you rotated the EFW is seems like there's a pinched line instead, also didn't that give you more vignetting ?

Thanks for sharing your experience

I'm inclined to agree.

Olly

[Magnum]

Microlensing is one of the well known drawbacks with the Panasonic CMOS sensor, though I still prefer it to the Starburst Amp glow of some of the other CMOS sensors. If I had to buy a CMOS sensor it would still be the Panasonic based cams such as the 1600 and just put up with the artefacts on bright stars as its the most CCD like CMOS sensor currently available in my opinion, but for the foreseeable future I will be sticking with my Atik CCDs. 

Lee

Edited February 18, 2020 by Magnum

[ollypenrice]

3 hours ago, Magnum said:

Microlensing is one of the well known drawbacks with the Panasonic CMOS sensor, though I still prefer it to the Starburst Amp glow of some of the other CMOS sensors. If I had to buy a CMOS sensor it would still be the Panasonic based cams such as the 1600 and just put up with the artefacts on bright stars as its the most CCD like CMOS sensor currently available in my opinion, but for the foreseeable future I will be sticking with my Atik CCDs. 

Lee

So will I.

Olly