Bloated stars - maybe UV/IR cut needed?

[kirkster501]

Hi all,

Been reading this article and its referenced links with interest.  I also seems to get bloated stars with the TEC140[with FF]/Atik460/Astrodon LRGB combination.  The stars become uncontrollable when moving into the nonlinear state.  I never get this with the FSQ85 and the Atik.

https://www.lightvortexastronomy.com/blog/bloated-stars-in-luminance-and-blue-through-a-refractor

What do you guys think?  I have an IDAS P2 2" to try that, I hope, should cut the UV/IR from flooding my scope.

Look at these images below and you will see what I mean.  Sure, the galaxies are nice but the bright and bloated stars take the edge off of the images.  M33 is with Baader filters so it is not the filters causing this.  Possibly I am stretching too aggressively but I don't think so.

Thanks, Steve

Edited July 29, 2020 by kirkster501

[ollypenrice]

Steve, let me send you some of my TEC140/Atik 460 data as a 16 bit linear TIFF stack for you to compare with your own. I have a lum stack on M101 which would give you a helpful comparison. PM me an email address and I'll send them via Dropbox if you'd like to try it.

If I give this data a set of pure log stretches, bringing in the black point as usual but doing absolutely nothing else to it, it looks like this when saved as a JPEG. How does this compare with yours? The only filter here was a Baader luminance. I'm using the TEC flattener.

I regard my TEC140 as giving the best stars of any refractor I've used including the FSQ106N (the old Fluorite) and the Baby Q. Before I had the flattener it did bloat on blue stars to some extent. Yuri Petrunin insists that the flattener has no effect on colour correction but, like a lot of his customers, I don't agree with him. (It may be an interaction between glass elements in the camera or filterwheel and the scope, so maybe not really to do with colour correction, but the flattener did improve my stars.)

The shots below show how the TEC140 has controlled Alnitak. A stack of 10 minute luminance subs with the linear image on the left and a pure log stretched version on the right. Absolutely no artificial control of Alnitak whatsoever.

I think this is an astonishing performance by the TEC. Maintaining Alnitak as a double was a complex processing job using multiple stretches and layers with the Tak data. With the TEC the optics did the lot. For all that, I do frequently individually process big stars from the TEC stacks. Masked stretching is vaguely helpful but I reverse-process them in Photoshop. That's another story but it beats masking!

Olly

 

Edited July 29, 2020 by ollypenrice

[kirkster501]

Thanks Olly, will ping you.

[ollypenrice]

57 minutes ago, kirkster501 said:

Thanks Olly, will ping you.

Done!

Olly

[kirkster501]

To complete this story, Olly shared with me his superb luminance of M101.  I am mightily happy that my scope is fine and his linear luminance stars are similar to mine.

The bloated large stars in my stretched images are a result of my stretching too aggressively without masks I think - something I need to investigate and skill up on.