Jump to content

NLCbanner2024.jpg.2478be509670e60c2d6efd04834b8b47.jpg

Saddlesore

ollypenrice

By ollypenrice
in Imaging - Deep Sky

Recommended Posts

  • Replies 38
  • Created
  • Last Reply
Naemeth

Naemeth

Posted
Posted

Beautiful image Olly, I can't help but think it looks just a bit 'fuzzy'. I'm not sure it's the right word but, at least on my laptop, it looks a tiny bit soft.

I do like it, and me being the only one to mention it makes me feel I'm imagining it :undecided: .

Brilliant detail though.

Link to comment
Share on other sites
ollypenrice

ollypenrice

Posted
  • Author
Posted

Beautiful image Olly, I can't help but think it looks just a bit 'fuzzy'. I'm not sure it's the right word but, at least on my laptop, it looks a tiny bit soft.

I do like it, and me being the only one to mention it makes me feel I'm imagining it :undecided: .

Brilliant detail though.

No, it's not you and I think you're right. I've tried everything I can to sharpen this up a bit (the Head part, at least. I don't like sharp stars.) However, faint dust doesn't give much signal and any sharpening goes straight to noise. Excuses excuses, but we didn't land on the best seeing while working on this one. For comparison Russ Croman's in a 20 inch F8 (ours is 14 inch F6.8) looks like this; http://www.rc-astro....id1071_big.html

I actually prefer our NGC2023 but he clearly has finer resolution on both the Head and the stars. It's a lovely image.

We still don't have a really convincing way to focus the ODK. Sorting this out needs to be my new year's resolution...

Olly

Link to comment
Share on other sites
Naemeth

Naemeth

Posted
Posted

No, it's not you and I think you're right. I've tried everything I can to sharpen this up a bit (the Head part, at least. I don't like sharp stars.) However, faint dust doesn't give much signal and any sharpening goes straight to noise. Excuses excuses, but we didn't land on the best seeing while working on this one. For comparison Russ Croman's in a 20 inch F8 (ours is 14 inch F6.8) looks like this; http://www.rc-astro....id1071_big.html

I actually prefer our NGC2023 but he clearly has finer resolution on both the Head and the stars. It's a lovely image.

We still don't have a really convincing way to focus the ODK. Sorting this out needs to be my new year's resolution...

Olly

Are all the subs slightly off-focus?

I was thinking that if some were sharp you could possibly replace some of the data.

I was thinking for checking the focus you could do several 5s exposures, 30s exposures and some of several minutes. If it's sharp there, it should be sharp at long exposures, because it's clearly not a tracking issue. Or, perhaps it could be some sort of thermal issue if the focus is slipping after a few minutes, you might need to do several 15 minute exposures to be sure there is no problem there.

I must say I think I prefer the colour of the Head on Russell Croman's picture, yours seems a little green/blue-ish. Difficult to compare NGC 2023 though, I'm sure if the focus is spot on I would be able to compare them.

HTH :).

Link to comment
Share on other sites
ollypenrice

ollypenrice

Posted
  • Author
Posted

It's hard to say if the focus could be improved. If I could improve it I would, of course. The trouble is that at this kind of focal length FWHM is pretty much a waste of time. It varies too much to contain any useful information so I study the diff spikes on a bright star. I do take decent sub lengths to do this. Any softness might also be seeing. Again, at this FL we are very susceptible to it. The smaller scopes, on a bad night, give about the same FWHM as on a good one but the 14 inch varies enormously.

Plenty of 'bad seeing' subs were discarded on this project. If you discard too many, though, you can't sharpen or contrast-boost because you explode instantly into noise. Resolution of detail is also about depth of signal...

Olly

Link to comment
Share on other sites
Naemeth

Naemeth

Posted
Posted

It's hard to say if the focus could be improved. If I could improve it I would, of course. The trouble is that at this kind of focal length FWHM is pretty much a waste of time. It varies too much to contain any useful information so I study the diff spikes on a bright star. I do take decent sub lengths to do this. Any softness might also be seeing. Again, at this FL we are very susceptible to it. The smaller scopes, on a bad night, give about the same FWHM as on a good one but the 14 inch varies enormously.

Plenty of 'bad seeing' subs were discarded on this project. If you discard too many, though, you can't sharpen or contrast-boost because you explode instantly into noise. Resolution of detail is also about depth of signal...

Olly

FWHM?

Hopefully the seeing will improve :).

Link to comment
Share on other sites
ollypenrice

ollypenrice

Posted
  • Author
Posted

FWHM?

Hopefully the seeing will improve :).

Full Width Half Max. It's a standard way of measuring the extent to which a star is in focus. The brightness is represented by a bell curve. Half way up the curve of brightness the width of the 'bell' is measured and the narrower the better. It works brilliantly with short FL instuments and diabolically badly with long ones, or in bad seeing! If ever you try it, go for longish subs, around three seconds, with a star that falls short of saturation or the bell gets its top cut off.

Olly

Link to comment
Share on other sites
chrissuddell

chrissuddell

Posted
Posted

Hi Olly,

I'm with the little out of focus theory here as well, and its also a little noisy. Your going to have to start again :-)

With the FWHM for focus, that ok, but I have seen some programs that use that and it does not always work due to seeing. It looks like this just needs a focus tweak.

Still a very good image though, but not upto your normal standards.

Chris

Link to comment
Share on other sites
vdb

vdb

Posted
Posted

Great Image, and soon I will have a go at the processing. On the sharpness, it's a crop, so yeah it's a bit soft,

maybe it's focus, my guess it's seeing + the fact we show a crop. If I look at the full frame it's not that pronounced, unfortunately we ran into reflections ...

/Yves

Link to comment
Share on other sites
ollypenrice

ollypenrice

Posted
  • Author
Posted

Yes, I should have said that is is only about a third of the full frame. Since I did the focusing I prefer the bad seeing theory!! I bust a gut focusing the L data, knowing how critical it would be, and I do think I got it to give what it could.

Sharp dust is a big ask...

Olly

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.