I particularly like working with rectangular fisheye lenses for my wide-angle macro work because they exhibit better good close-focusing capability than normal ultra-wide lenses. I have extolled the virtues of the Sigma 15 mm f/2.8 rectangular fisheye on many occasions when I was using it on APS-C format (with Nikon bodies and with a Sony NEX 7). Using a lens like this, designed for full frame, with formats smaller than that, permits the utilisation of the centre part of the image circle. The images then show remarkably little distortion – just a bit of curvature towards the edges: sharpness is excellent as is contrast and the close focusing capability is remarkable. In fact, this was the main lens that both Clay Bolt and I used when gathering images for our e-book: Wide-Angle Macro | The Essential Guide.
Of course, I can use also this lens with the micro 4/3 (MFT) format and a suitable adapter (Nikon to micro 4/3) but then it behaves as a 30 mm wide-angle compared with 22.5 mm forAPS-C, that is, unless you use the Metabones SpeedBooster. Then with the model I use it behaves as a 19.2mm lens with a maximum aperture 1 1/3 times wider than f/2.8…around f/1.8 – but more about that in the next post.
With a change of format to MFT, I wanted to go that bit wider…
Samyang 7.5 mm f/3 .5 rectangular fisheye