I am looking at which 90mm lens I am going to get to match my 210mm APO-Symmar f/5.6, and have come up with the following choices:
1) Schneider 90mm f/5.6 Super Angulon MC
2) Schneider 90mm f/5.6 Super Angulon XL
3) Rodenstock 90mm f/4.5 Grandagon-N
The prices are all okay with me, with the MC Schneider being a little cheaper.
All of my past experiences tell me that when it comes to wide angle lenses, I should spend a little more and get the better lens, otherwise I will be sorry. Therefore I lean towards the XL or Grandagon-N (what is the Sinaron and Caltar name for this lens?) I prefer a lens which is usably sharp in the corners wide open, even if I do need to pay a little more for it.
I am wondering how useful the wide open settings are for each of these lenses. From what I have read, the widest setting is sometimes sharp in the middle, for focusing with a bright image, but not so sharp in the corners. What are these three lenses like wide open, in the corners? Are the corners usable wide open for focusing, and for imaging?