Bloaty blue stars - any thoughts on cause?

[Mr Thingy]

@alacant

Just starting to process but in the meantime I compared the relative star sizes between each filter.

Not much separating the Ha, R & G, but the blue is clearly much more bloated.

[DuncanC]

Other posibility is the filters aren't par-focal. Did you check focus between filters? Could it be a simply focus issue due tot he colour change?

[Mr Thingy]

48 minutes ago, DuncanC said:

Other posibility is the filters aren't par-focal. Did you check focus between filters? Could it be a simply focus issue due tot he colour change?

After seeing that the R and G filters were parfocal I skipped refocusing with the blue but when I saw the first exposure, with the bloaty stars, I stopped and ran the autofocus routine. 

With the help of this discussion, I think it could be a combination of scope and filter (can't rule out user error in my case though!)

[Mr Thingy]

Here's my first crack at processing the image - or any RGB image for that matter!

I'm going to redo it now I have a better handle on what I'm doing - I made a few errors aling the way.

Pretty sure I can bring more nebulosity out. Colours don't seem quite right either.

 

Edited February 19, 2021 by Mr Thingy

[The Lazy Astronomer]

That's a very pleasing image. ☺ Not exactly a shortage of nebulosity in there either!

If you reprocess, see if you can get the OIII teal-ish colour in the core. Can't for the life of me bring it out in my image, but I'm assured it definitely should be there!!

[Mr Thingy]

7 hours ago, The Lazy Astronomer said:

That's a very pleasing image. ☺ Not exactly a shortage of nebulosity in there either!

If you reprocess, see if you can get the OIII teal-ish colour in the core. Can't for the life of me bring it out in my image, but I'm assured it definitely should be there!!

Thanks! I think the luminance layer is too dominant at the moment and I need to boost the colours. Just got to figure out how to do that. 

[Mr Thingy]

I managed to use some processing tools to tone down the bloat. It's still visible but definitely reduced.

Using Ha as luminance didn't work out well i  the end as it obscured some features (I guess those not emitting in Ha!), particularly in the nebula to the left, so I tried using the red and green data to make a luminance layer, as between them they seemed to contain all the structure. I think it worked OK.

I'm very happy with the image, though it looks much nicer on my computer versus here on my phone. I might actually get this printed! 

Thanks to @AstroRuz for the youtube video on reducing star size. I applied to the blue channel to get the bloat down.

-Thingy-

[Adam J]

It's a fast ish doublet so this is expected. As someone else above recommended I would grab a 2 inch Astronomik L-3 and place it in series with the LRGB filters. 

[Mr Thingy]

20 hours ago, Adam J said:

It's a fast ish doublet so this is expected. As someone else above recommended I would grab a 2 inch Astronomik L-3 and place it in series with the LRGB filters. 

Yes, definitely an option, though I'm debating whether just to live with it and learn to try and minimise as best I can whilst I learn the ropes of AP, then divert my money into eventually getting a 'scope that handles colours better and use the 72ED for narrowband imaging. 

Despite the bloaty blue stars I'm pretty pleased with the image and thanks to SGL members I have a greater knowledge now on the cause and how to mitigate.

Cheers

[alacant]

Here are some fat bloated blue stars taken with a €6000 refractor and a €eye-watering camera.

Compared with our 72eds, there's not much in it.

 

 

 

[Mr Thingy]

Can't decide on whether to get an Astronomik L3. Not sure on the extent to which it will improve things, plus it's another bit of glass in the optical pathway.

Decisions, decisions.

I looked back at my first image, a mono shot taken with my Luminance filter and the stars are very bloaty, so it's tempting to get an L3.

Does anyone have any experience of how much this filter improves things?

[The Lazy Astronomer]

6 hours ago, Mr Thingy said:

Can't decide on whether to get an Astronomik L3. Not sure on the extent to which it will improve things, plus it's another bit of glass in the optical pathway.

Decisions, decisions.

I looked back at my first image, a mono shot taken with my Luminance filter and the stars are very bloaty, so it's tempting to get an L3.

Does anyone have any experience of how much this filter improves things?

In my experience, the difference is significant. The L3 greatly reduced bloating in L and B channels.

I was out earlier with my planetary camera and took a couple of single 20 second subs of a random area near Polaris: one with the ZWO luminance filter and one with the L3 filter, pictures attached.

I had to stretch them a bit, because the difference wasn't really visible in the linear data, and to be honest the difference still doesn't look massive, but the halo is definitely larger with the ZWO filter (much more obvious if you download and flick between them) - if l was smarter, I'd have found a big bright blue star to do this with. 

No idea why the ZWO one has the whole pacman thing going on either...

[Mr Thingy]

5 hours ago, The Lazy Astronomer said:

In my experience, the difference is significant. The L3 greatly reduced bloating in L and B channels.

I was out earlier with my planetary camera and took a couple of single 20 second subs of a random area near Polaris: one with the ZWO luminance filter and one with the L3 filter, pictures attached.

I had to stretch them a bit, because the difference wasn't really visible in the linear data, and to be honest the difference still doesn't look massive, but the halo is definitely larger with the ZWO filter (much more obvious if you download and flick between them) - if l was smarter, I'd have found a big bright blue star to do this with. 

No idea why the ZWO one has the whole pacman thing going on either...

Thanks for going to the effort to show that comparison. Very helpful indeed 😁

The difference doesn't look massive but also good to hear your opinion that the difference is significant.

I think I will order myself one.

Thanks again.

[Mr Thingy]

On 26/02/2021 at 02:07, The Lazy Astronomer said:

In my experience, the difference is significant. The L3 greatly reduced bloating in L and B channels.

I was out earlier with my planetary camera and took a couple of single 20 second subs of a random area near Polaris: one with the ZWO luminance filter and one with the L3 filter, pictures attached.

I had to stretch them a bit, because the difference wasn't really visible in the linear data, and to be honest the difference still doesn't look massive, but the halo is definitely larger with the ZWO filter (much more obvious if you download and flick between them) - if l was smarter, I'd have found a big bright blue star to do this with. 

No idea why the ZWO one has the whole pacman thing going on either...

Finally made my mind up and ordered a set of astronomik RGB filters and an L3 to go with them.

I debated throwing that money towards an APO triplet, but I guess I'd still need better filters in order to do that justice, so I'll get filters then maybe an APO somewhere in the near future.

Hopefully these filters will tame the bloat 🤞

[The Lazy Astronomer]

6 hours ago, Mr Thingy said:

Finally made my mind up and ordered a set of astronomik RGB filters and an L3 to go with them.

I debated throwing that money towards an APO triplet, but I guess I'd still need better filters in order to do that justice, so I'll get filters then maybe an APO somewhere in the near future.

Hopefully these filters will tame the bloat 🤞

I'll be interested to see the results you get with the rgb filters, I keep thinking l want to upgrade mine (pretty sure the ZWO ones are causing reflections in my images).

[Mr Thingy]

7 hours ago, The Lazy Astronomer said:

I'll be interested to see the results you get with the rgb filters, I keep thinking l want to upgrade mine (pretty sure the ZWO ones are causing reflections in my images).

I'll post a comparison when I get a chance. 

I get a lot of reflections and halos with my Zwo filters, so I hope the Astronomik ones decrease/eliminate those as much as they claim.

I didn't know enough about the subject when I bought the Zwo filters last year but now when I look back at the transmission chart, there's a very notable part absent; the X-axis starts at 400nm so you can't see at all how it performs in the critical range below that.