Originally posted by madbrain I will say however that I'm not fond at all of the cheap adapters. I tried some before for wide angle with the da 18 55, and there was terrible vignetting. When I did some PP to remove vignetting, the FOV was almost the same as without the adapter. It was basically useless. That was a big reason why I got the sigma 10 20 in the first place.
I suggested the 0.25x FE adapter as a cheap way to find whether full-circle or frame-filling FE suits you more (or at all). Full-circle FE does more than merely 'vignette' -- it's a full image circle surrounded by black space! Such images should be cropped square, maybe mounted in a circular matte. Frame-filling ~180-degree FE (like the Samyang 8, or DA10-17 @10mm, on APS-C) doesn't vignette, but it's also not really suitable for flattening-out by defishing. Even the Sigma 15 or Zenitar 16, or the DA10-17 @17mm, don't do well with full defishing.
IMHO defishing is rarely worth the effort. If you want rectilinear pictures, stick with your 10-20 UWA. If you want rectilinear images wider than its ~100-degree maximum view, stitch-up some panoramas. There's no magic bullet here. Fisheyes give bendy distortion, and rectilinear UWAs give stretchy distortion, and that's reality. To avoid distortion, shoot a series with a 28mm lens in portrait (vertical) aspect and stitch them together. That is the *only* distortion-free option AFAIK.
Quote: The DA 10 17 is not in my price range, and also lacks an aperture ring, therefore I would not consider it.
Price range, I understand. It's not cheap. It's the lens that drove me to Pentax because there was nothing comparable at anywhere near the price -- and there still isn't. But do *any* of these fishies have aperture rings? I haven't checked. The old Vemar-Sigma 12/8 has an aperture ring, if you don't mind f/8-11-16 Waterhouse stops. It merely lacks a focus ring!
My argument against FE primes: They're one-trick ponies. And that trick can get tired pretty quick.