NGC 3372 in Ha

[Atmos (Colin)]

It is really nice Chris, lovely FOV. Feeling like a mosaic to match Andy?

Are you using the Vixen 0.67x FR? What I am thinking is that even if you have the spacing correct it'll probably not look crash hot around the edges as it is designed for a F/7.7 system. As it isn't made for telescope it may be over or under correcting at the edges, changing the focal spacing may help but it could simply be an artefact of using that FR on that scope.

The seagulls in lens are a combination of uncorrected field curvature and astigmatism (my Nikon 50mm F/1.8D has it BAAAAAAAAAD).

https://dl.dropboxusercontent.com/u/...of%20stars.jpg

[lazjen (Chris)]

Yes, that looks familiar.

I was using this FR: http://www.teleskop-express.de/shop/...or-GSO-RC.html

It works really well for my GSO RC10 - I think it does some field flattening as well? Anyway, it's totally unsuitable for the Sharpstar and goes into the category of "what the heck was I thinking?".

As for doing a mosaic of that area - baby steps. I'd really like to actually get more than 1 channel of data for a target!

[Atmos (Colin)]

Well that explains the problem then, it flattens the field by correcting for astigmatism (RCs don't have field curvature as such) so that'll be the culprit