Ain’t she beautiful?
I have been debating the purchase of the Sigma 4.5mm circular fisheye for at least the last year, but perhaps more like 2 years. This lens is currently the one and only circular fisheye lens designed for APS format cameras. Most circular fisheyes you will find are 8mm and are designed to produce a circular image on a full frame camera. The biggest beef I have about the Sigma 4.5mm is that the image circle is too small for ordinary APSC format found in Nikon and Sony dslr’s so that it can accommodate Sigma and Canon cameras which have smaller format sensors. This means that on the larger sensor of my Sony cameras, there is a lot of wasted black space in the image. Ideally, a circular fisheye should be designed to fill to the edges of the narrow portion of the image to maximize coverage while still getting a circular image.
The small image circle means many pixels get wasted and will need to be cropped out. It also means that it is a lot less useful for one of my primary purposes for such a lens – 360VR’s. The lower resolution shots from the lens will obviously mean lower resolution 360VR’s and for those resolution makes a huge difference. The main advantage to using a circular fisheye over a diagonal fisheye or even a wideangle is that you can do as few as 3 shots to get complete coverage, where with a diagonal it takes 6-10 shots and with a wide even more.
Now that Sony has announced the new a77 with 24MP sensor (which I have pre-ordered), this lens has become a lot more appealing. I should be able to achieve approximately 38MP 360VR’s while taking only 3 shots. That is pretty good considering I only get 66MP with my current diagonal lens – the Rokinon 8mm. These numbers may seem quite high, but when you consider the wide field of a 360VR, you quickly realize the resolution is not all that much.
Until the a77 arrives this lens will primarily be used on my a55 where it can produce about 17MP 360VR images, not too shabby for web uses and practicing. It also partially fills in that hole I’ve felt since I sold off my Sigma 10mm last year – its a great lens but I just realized the Rokinon has better IQ and I couldn’t keep both.