Quote:
Originally Posted by JA
Whilst I haven't tried with the ASI071, I have used various wide lenses with various DSLR fullframe bodies for astro. In this use coma and astigmatism are often obvious abberations that you will have to contend with particularly at wider apertures. Certainly you will get the wider view that you want with the larger sensored ASI071, but you will also expose limitations in the optics as you start to use more of the image circle of the lens compared with using that same lens on the smaller sensors you mentioned: i.e: The likely abberations you were concerned with (probably coma and astigmatism) will get worse.
Correcting any error (if there is one) in the flange-to-sensor distance may improve the situation, but that's unlikely to be in error if you are using a one piece camera adapter. Maybe there is some load induced tilt, depending on lens support/play.
Stopping down will certainly improve the situation as the sensor sees less of the lens and its potential edge abberations, but the real improvement will probably unfortunately only be with a different lens, unless of course the Canon 35mm f/1.4 you have is the Canon EF 35mm f/1.4 USM L II which is EXCELLENT. The previous version, the Canon EF 35mm f/1.4 USM L suffers from very significant coma and astigmatism. See excerpt below prepared from lenstip.com comparing it with the new version II. The new version is quite expensive, but if you want to get most/all of the way there you could consider a significantly less expensive Sigma 35mm f/1.4 Art lens or Sigma 40mm f/1.4, also excellent.
Edit added: You could also try a Samyang 14mm f/2.8 UMC for your 180 degree vista and you would only need 2 panels. It is very sharp edge to edge with very low coma. I haven't experienced it, but some complain of QC issues and sample variation with this lens. Another possibility if you are adventurous is the Nikon 14-24 f/2.8 which is also very well regarded and I've heard of Canon Astro shooters adapting it for their use on Canon bodies due to its sharpness and low coma. Best
JA |
Thanks JA - good detailed information there which has got me thinking about the problem a bit deeper - especially the part about using more of the image circle and the inherent distortions the further out you go. By the way I use a Sigma 35mm F1.4 Art not the Canon.
I dont want to go too wide as star size and detail are affected. I've been doing some amazing Milky Way mosaics lately with my 6D and Samyang 135mm F2 but of course they take a long time to image and even longer to process and create the mosaic. But I want cooling (ideally set-point) and more Ha data. (theres a CentralDS modified & cooled 6D for sale in the IIS classifieds at the moment - that's why I'm looking at all this - versus for a similar price an 071MC Pro)