Fuzzy Tadpoles - with donuts!

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.

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.

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

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.

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!

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)

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.

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

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.

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... 😊 

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

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...

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.