View Single Post
Old 01-05-2021, 10:31 AM
Atmos's Avatar
Atmos (Colin)
Ultimate Noob

Atmos is offline
Join Date: Aug 2011
Location: Melbourne
Posts: 6,910
Originally Posted by alpal View Post
Hi Colin,
I've never heard of seeing that good in Melbourne.
I think the best I ever measured from any single frame
was 2.8 arc seconds FWHM in Ha.

I have never measured a final stack - only individual frames.
Are you sure you had the correct information loaded
into Maxim DL or whatever you were using to make the measurement?
On some nights the seeing was as bad as 6 arc seconds FWHM.

The best seeing I've ever heard of in Melbourne
before tonight was at Mt Macedon -
close to Melbourne -
FWHM of 2.2 arc seconds.

I make my decision as to whether I continue imaging early on in the night depending on how the auto focus is coming along but also how MaximDL deems the FWHM. When I do my proper measurements though it's all done in PI and done manually where I select at least a dozen stars. I know my pixel scale (0.4") and if a bunch of stars measure 3 pixels then I know I have 1.2" seeing.

Here are three crops. NGC 288 measures at 1.48" first off. Next is NGC 6752, a forgotten globular near NGC 253, it measures down to 1.42". Lastly is a crop of Eta Carina, actually cannot remember exactly what it was but it wasn't as low as those globulars; might have been around 1.8-1.9".
Attached Thumbnails
Click for full-size image (NGC 288.jpg)
169.6 KB65 views
Click for full-size image (NGC 6752.jpg)
186.2 KB61 views
Click for full-size image (Eta Carina.jpg)
181.6 KB92 views
Reply With Quote