Widefield Image Help

[Scott Tilley]

Managed to get the camera out for an hour last night and managed to find a spot of sky that had the least thin cloud and where I was avoiding the smoke from a neighbours bonfire. This was shot with a Canon 450D astro modded and a Tokina 11-16  lens ISO 800, F.3.2 at 16mm. There is about 50 minutes of date here made up of 180 second subs. I know my processing skills are rubbish and I have to work on it but I am a bit disappointed with the star distortion at the edges of the frame. Does anyone know if this is normal for this lens or is it something I'm doing? Thanks for looking.

[Knight of Clear Skies]

Could you post a single sub for comparison please? I've sometimes had problems with DSS producing extra distortion when stacking.

[wxsatuser]

Unfortunately it will never be that good around the edges.

It's very best should be at 14mm @ f/5.6

[Scott Tilley]

Here's a single sub. All the same I think!

Thanks for the help!

[Scott Tilley]

Unfortunately it will never be that good around the edges.

It's very best should be at 14mm @ f/5.6

It's interesting to know what its sweet spot is. I will try it at this setting next time out. Unfortunately I couldn't find any in depth review of the lens for astro imaging so wasn't sure what to go for.

Thanks

Scott 

[Owmuchonomy]

Well, I can recognise Orion, Taurus, M45 and right on the top, the California nebula. Getting the final image is quite a journey. Processing skills still elude me after 2 years of trying.

[wxsatuser]

It's interesting to know what its sweet spot is. I will try it at this setting next time out. Unfortunately I couldn't find any in depth review of the lens for astro imaging so wasn't sure what to go for.

Thanks

Scott 

You can see the graphs on Photozone.

To be good around the edges it needs to be excellent on three bar graphs

Most lenses we have to settle for some abberations.

[michaelmorris]

Stopping down the lens should help with the edge distortion, but will obviously reduce the number of photons collected.  The only way around this would either be taking many more subs or longer subs on a tracking mount.

Why not try some test shots at different f-stops to try to find the sweet spot?  If you have Photoshop, there is a 'lens correction' function that can help correct some of the edge distortion. http://photoshopcafe.com/tutorials/lens_distortion/lens.htm

[Scott Tilley]

Stopping down the lens should help with the edge distortion, but will obviously reduce the number of photons collected.  The only way around this would either be taking many more subs or longer subs on a tracking mount.

Why not try some test shots at different f-stops to try to find the sweet spot?  If you have Photoshop, there is a 'lens correction' function that can help correct some of the edge distortion. http://photoshopcafe.com/tutorials/lens_distortion/lens.htm

Hi, thanks for the information. I think I need to upgrade my copy of photoshop, I have photoshop CS I think its so old it doesn't have any of these filters!! I will certainly have a go at finding the sweet spot on the lens.

Cheers

Scott