72ed big fat blue refractor stars

[alacant]

Hi everyone

Could anyone tell me if this is what we can expect? It seems rather shot-quiqly-with-an-old-achro style. Unfortunately I can't find anything with which to comapre. Maybe just my processing but i would have thought even a cheap doublet would produce less blue than this.

Please tell me I'm mistaken! Must say, I like the FOV it gives.

SW 72ed with ff tsflat2 at 128mm.

TIA and clear skies

 

[Rustang]

It doesn't necessarily answer your question but I've seen no blue with my SW 72ED DS PRO, could it be the field flattener causing it!? 🤔 how did you get the SW's 420mm fl down to 128mm or have i miss read that!?  Someone with more experience will probably be able to help more. 

Edited September 11, 2020 by Rustang

[alacant]

5 hours ago, Rustang said:

the SW's 420mm fl down to 128mm

Hi and thanks for your reply.

Do you have an example with bright stars? it would really help us decide.

128mm is the working distance from the ff to the camera chip for fl 420mm. I suppose it could be the ff or maybe just the bright stars. I tried a different field with fewer bright stars and it came out better. Maybe need to adjust the processing. lightly does it perhaps.

Cheers and clear skies

[catburglar]

I think you’ve just pushed the processing a bit too far- there are dark haloes around many of the stars suggesting that the deconvolution is a bit too fierce or your star mask wasn’t quite generous enough...The image is also stretched quite hard so you get white cores and accentuate the haloes....

Startools has a nice ‘fringe killer’ filter that allows you to selectively reduce these blue haloes, but the best first step might be to go gently with the post processing...

[alacant]

2 minutes ago, catburglar said:

go gently

I think you're spot on, and yeah, I'd forgotten about st's fringe killer.  One more go with st and I think I'm nearly there. Also reminder to self not to process in a sunlit room.

This is where it stands:

[Ken82]

I can see some star halos from the filters other than that quite nice. Very similar to mine, absolute bargain! I think the halos make it look worse than it actually is. 

baader filters ? 
 

ken 

[alacant]

8 hours ago, Ken82 said:

filters

Hi

Thanks, no filters though. 

In the end, I just cheated!

 

[Rustang]

9 hours ago, alacant said:

Hi and thanks for your reply.

Do you have an example with bright stars? it would really help us decide.

128mm is the working distance from the ff to the camera chip for fl 420mm. I suppose it could be the ff or maybe just the bright stars. I tried a different field with fewer bright stars and it came out better. Maybe need to adjust the processing. lightly does it perhaps.

Cheers and clear skies

This was one of my first attempts at the Heart Nebula before I learnt how to reduce the stars in post, captured with my 72mm. It has some bright stars but not the biggest. 

[happy-kat]

I use the fringe killer on any stars I've missed but I now prefer to create a star mask excluding the CA effected stars before I then apply colour using StarTools.

[alacant]

1 hour ago, happy-kat said:

the fringe killer

Yeah, thanks. I'm gonna have to rethink this. Maybe mosaics with a reflector is the way to go...

Anyway, not given up yet. I'll try with a uv-ir tonight. I seem to remember that that gave some improvement to an 80ed I once suffered!

Cheers

[happy-kat]

That was meant to read inverted selective star mask, I basically don't colour the CA effected stars at all effectively leaving them as luminance.

[SteveBz]

On 12/09/2020 at 06:46, alacant said:

Hi

Thanks, no filters though. 

In the end, I just cheated!

 

I thought I recalled that you were a Siril user. Is this the color photometry correction, or something else?

[alacant]

4 hours ago, SteveBz said:

a Siril user

I used Siril for calibration and stacking. This is a 10 minute thrash in st.