Fuzzy Tadpoles - wi...
 
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2022-05-29: APP 2.0.0-beta2 has been released !

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windows 2.0.0-beta2

macOS x86_64 2.0.0-beta2

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Fuzzy Tadpoles - with donuts!


(@devonshire)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
Topic starter  

Hi!

First real light with a new L-Extreme filter on my modded Nikon D5300, SV 102EDT 102/621mm, Hotech FF.
Stacked about 6hrs lights + flats + bias with APP 1.082 and Tab 2 'align channels' ticked.

Tab-0 Ha-OIII extract Ha came out pretty nice, but the Ha-OIII extract OIII is a problem.
Same settings for each stack, with the exception of Tab 0.
The OIII is fuzzy, with star donuts.

Pix attached.

This can't be right - what should I do differently?

Thx!

- Bob

Screenshot 20201113 OIII
Screenshot 20201113 Ha

 


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(@astrogee)
Red Giant Customer
Joined: 4 years ago
Posts: 135
 

Well I can tell you the first image is simply out of focus. The donuts you see are classic defraction patterns of out of focus stars.


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(@devonshire)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
Topic starter  

Just to be clear, the two samples above are (respectively) OIII and Ha extracts from the same stack, and so were taken with the same focus.


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4919
 

The first one is a close crop I guess? The second one is zoomed out but also seems a bit out of focus.


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(@devonshire)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
Topic starter  

Nope.  They are of the same area of the same stack, close as I could get it. 

Look for the tadpole heads and the two matching stars below the tadpole on the right.


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4919
 

Oh, that is really weird. I would need to check the data to see what might be going on. You don't need to "align channels" btw, just select the extract algorithm in tab 0, load in the data and process. Then clear everything, change the algorithm in 0 to OIII, and process again. If that doesn't work, please upload the data here;

Go to https://upload.astropixelprocessor.com and use upload1 as username and upload1 as password.

Create a directory named “devonshire-haoiii-issue” and upload in there. Thank you!


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(@devonshire)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
Topic starter  

Thanks! 

Yup.  Did not make sense to me, either.  

Just to be clear, you're asking me to basically just re-run the stack, probably with 'Align channels' off?    Anything else?

And if it comes out the same, upload?  (approx 5GB)


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4919
 

Yes indeed, just use all automatic and standard settings, only thing you change is the algorithm in tab 0. And clean (or restart APP) and reload with the other algorithm. Just to double check if that works.


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(@devonshire)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
Topic starter  

Vincent,

I repeated the exercise as you described - same result.

Then, I repeated the exercise with images on the same target, taken previously with my Starfield 0.8 FF (vs. the 1.0 Hotech) and CLS-CCD (vs. L-Extreme), just after the camera was modded. This was improved. Discrepancy in focus and star size was there, but less noticeable.

Then, I dug out an old Horsehead I'd shot, before I acquired either field flattener or filter, just with a UVIR filter and processed it the same way. Better yet.

Maybe not a processing problem, although anything that APP could do to tighten stars across channels would be appreciated. 🙂

My intention, (if the skies ever clear...) is to take the Hotech off, and shoot the Tadpoles again with just the L-Extreme in the optical path and see what I get.

- Bob


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(@astrogee)
Red Giant Customer
Joined: 4 years ago
Posts: 135
 

If you're getting different performance with FFs, maybe the backfocus is not properly set. It seems most FFs have a 55mm back focus - but my older FF is 45mm that required a special low profile camera adapter - and its not easy to find this value sometimes. May have to contact manufacturer.


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(@devonshire)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
Topic starter  

I've been through the spacing exercise with both of them, and going by the star shapes on the edges, they're about as good as they're going to get.

I think this is more to do with how many pieces of glass that dual-narrowband image has to push through, and how much it diffracts along the way.  I know from posts by the filter-wheel crowd that they need to adjust focus between (say) Ha and OIII.  Well, photons are photons....   My current speculation (and of course that's all it is until the empirical evidence lands in), is that the extra glass in the path is accentuating that problem.   

Only time will tell... 😊 


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4919
 

How interesting, thanks for sharing your trouble-shooting, will help me to diagnose these edge cases better as well. 🙂 Hope it gets fixed!


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(@devonshire)
White Dwarf Customer
Joined: 4 years ago
Posts: 23
Topic starter  

Vincent,

Lousy weather lately, and while I was able to get out a couple of days ago, I was not able to get as much time-on-target as before, so images from that session are not directly comparable.

But. I think I do see the problem, and it's not APP.

It's a focus issue. When I am focusing, I'm doing FWHM with BackYard Nikon on the image that's being captured, which contains both bands from the L-Extreme. But the two bands are focusing at different points - same problem as the filter wheel crowd has.

Doesn't look too bad on the raw, but split the Ha and OIII out and it's a coin toss as to whether one or the other will be fuzzy, or maybe split the difference. In this last test, the OIII was sharper and the Ha was fuzzier.

I do think that the extra glass in the flattener made this worse, but the root cause is probably the objective itself, as that and the filter were the only things in the path this time. Sigh...

 


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(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4919
 

Thanks for that! That does seem a bit strange, I wouldn't expect such a big difference, otherwise many people with these dualband fiters would see the same. Maybe something in your setup is indeed making a slight difference (if there is at all) that much bigger. Difficult to say, but glad to see you're on to something.


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