California nebula

[RobertM]

This started out being a quick shot whilst waiting for something else to get high enough but ended up being a bit of a labour of love.  In the process I'd found out that all the previous shots I thought I'd taken with the 200mm lens stopped down were in fact at full aperture ( f/2.8 ).  This one is taken with the lens properly stopped down to f/3.2.  I have more exposures to add in the future but some of the existing subs had dewing/frosting issues, subsequent use of RC Gradient Exterminator removed some nebulosity and I messed up my dark library in the process so calibration is a bit iffy.  Need to sort out my darks before finishing it off.

As well as NGC1499 you may also notice an old planetary nebula that appears as a circle about 3/4 degree in diameter cutting into the North West (North is up West is right) part of the main nebula.  FOV is roughly 250 x 340 arcmin.

Exposure: 8 x 30min
Filter: Baader Ha 6nm passband
Camera: Finger Lakes ML 8300
Optics: Canon 200L lens@f/3.2
Conditions: Clearish but full moon (affecting contrast badly)
Date: 01/01/2010
Guiding: 50mm finder



Full res: http://farm3.static.flickr.com/2741/4238477498_549a592368_o.jpg

[Fay]

Looks very good to me Robert, fits in the frame nicely. 30 mins subs!!!!

[MarkS]

That's an excellent result Robert - very tight stars and lots of detail.  That 200mm gives you a really useful FOV and the fast F-ratio also helps enormously.  It's an excellent result for a full moon night but from a darker site I'm sure the result would be stunning.

Do you really notice the difference in aberrations between F2.8 and F3.2 or do you simply use F3.2 to give you diffraction spikes

I'll have to give GradientXterminator a trial sometime.  Up to now I've been masking off stars and nebulosity; applying a very strong blur; then subtracting the result from the original.  But it's very labour intensive and requires a few iterations.

Mark

[RobertM]

Do you really notice the difference in aberrations between F2.8 and F3.2 or do you simply use F3.2 to give you diffraction spikes

Good question but it this case it makes a lot of difference towards the edge and corners.  If you compare this image with the NGC7000/Pelican wide field then you'll see what I mean.  I would rather not have to stop it down as the exposures need to be 50% longer for the same ADU (assuming 1/2 stop) but I do like nice pointy stars.  The spikes are interesting; I would have expected 8 with this lens but there are only 4.  I've read on other forums that it's entirely possible they're on chip microlensing artifacts, will have to see if Chris gets the same issue with his camera and fast lenses.

Gradient exterminator does exactly what you're doing but with less effort (and you can ignore stars) but it still requires a couple of itterations.  The other alternative is DBE in Pixinsight LE V1.02 (freeware); that isn't available anymore but I have a copy you're welcome to.  It's more flexible, easy to use and has lots of twiddly bits to play with so may appeal to the geek in you

Robert

[MarkS]

The spikes are interesting; I would have expected 8 with this lens but there are only 4.  I've read on other forums that it's entirely possible they're on chip microlensing artifacts

You expected 8, and 8 is exactly what you have.  What do you mean there are only 4?

I've never heard of artifacts caused by microlensing - how does that work?

Mark

[The Thing]

It's lovely image. If my stars were half that sharp and pointy I'd throw a party instead of wanting to throw my scope out.

[RobertM]

You expected 8, and 8 is exactly what you have.  What do you mean there are only 4?

You're right, I was thinking about those images I've taken with the lens wide open - Doh, heads in a bucket !!!

[JohnP]

Looks great Robert & well done on spotting the 'circular planetary' never seen/ heard of this before. When I first looked at the image the stars are so pin point/ small & plentiful they almost look like 'hot pixels'.. Better on the full size though... Did you apply any noise reduction to the image the nebula looks so damn smooth...

Also I spotted the feint remains of a satellite trail or like top right part of the image...but I'm sure you knew that was there...

Great image & lovely FOV.

John