Seeing and The Elephants Trunk

[Craig123]

Hi all

I imaged a few hours ha on the Elephants trunk last clear skies. I used Fwhm on artemis capture to focus throughout and noticed the numbers were jumping around quite alot..I'm assuming this means the seeing was not good ( I noticed  comments on online astro pages to that affect too ). Having stacked the subs the stars look pretty big so iam hoping to get advice on what folks do about bad seeing. Do you image all night  hoping it will improve and then look only for subs that appear to be OK or just pack away again and wait for another clear night... or shrink stars in PP. ???

TIA

[alacant]

Hi. I had the same at the weekend. Stars jumping around, but very clear sky. Dilemma. Went ahead anyway and discarded the highest fwhm frames before stacking. The result was OK. A plot helps you decide which to throw away. HTH.

 

[ollypenrice]

You're right that the FWHM is bouncy in bad seeing. It can help to take longer subs so that the star's image averages out a bit making the values more stable. I usually use 3 second FWHM subs but might double this on unstable nights. It won't solve the problem of the final image but it makes focus as reliable as possible - and less irritating. 

After that, with a mono camera I would shoot only the colour. Loss of resolution won't much matter, as we know from the fact that it can be binned 2X2 without much detriment. Wait for a better night for the luminance. Whether you should also wait for good seeing to shoot Ha depends on the target. Sometimes the Ha contains lovely fine detail, in which case wait, but sometimes it just contains swathes of soft nebulosity or strings of beads in some galaxies, in which case bad seeing will do.

Olly

[Craig123]

1 hour ago, ollypenrice said:

You're right that the FWHM is bouncy in bad seeing. It can help to take longer subs so that the star's image averages out a bit making the values more stable. I usually use 3 second FWHM subs but might double this on unstable nights. It won't solve the problem of the final image but it makes focus as reliable as possible - and less irritating. 

After that, with a mono camera I would shoot only the colour. Loss of resolution won't much matter, as we know from the fact that it can be binned 2X2 without much detriment. Wait for a better night for the luminance. Whether you should also wait for good seeing to shoot Ha depends on the target. Sometimes the Ha contains lovely fine detail, in which case wait, but sometimes it just contains swathes of soft nebulosity or strings of beads in some galaxies, in which case bad seeing will do.

Olly

Thanks Olly.. So if I was doing NB on IC 1396 it might be better to do Sii or Oiii on this target as there seems abit less detail there than the Ha. 

Maybe I will try and salvage some good ones from this session and go at the Ha  again. 

[Craig123]

1 hour ago, alacant said:

Hi. I had the same at the weekend. Stars jumping around, but very clear sky. Dilemma. Went ahead anyway and discarded the highest fwhm frames before stacking. The result was OK. A plot helps you decide which to throw away. HTH.

 

Phew so it's not just me getting the jitters setting up this week. Thanks for the idea of stacking best fwhm. I will have to look in to that in astroart. 

[gorann]

Seeing is a luxury problem. Here in Sweden there have been no stars to be seen for the last two weeks?

[Craig123]

25 minutes ago, gorann said:

Seeing is a luxury problem. Here in Sweden there have been no stars to be seen for the last two weeks?

We are not far behind here.. I lugged all my stuff out last night.. Aligned. Framed target, focused and on the 18th minute of a 20 min sub the clouds appeared.Session over. ???