Sigma 8mm f/4 EX Circular Fisheye
(From Sigma lens literature) This circular fisheye lens is used to produce circular images with an angle of view of 180 degrees when attached to a full-frame digital or 35mm film SLR camera.
This unique lens is used to produce circular images with an angle of view of 180 degrees and also incorporates an auto focus system to get accurate focusing that might be difficult through the finder due to its extremely large depth of field.
This lens can be used for the scientific applications such as the solid angle measurements of cloud distribution over the sky, and vegetation distribution of forests, due to the quantifiable angle/area relationship it produces.
Also supplied with the lens is a fitted padded case and a gelatin filter holder at the rear, allowing the use of gelatin filters.
Sigma 8mm f/4 EX Circular Fisheye User Reviews
9 out of 10 points and recommended by Ross_Alford (36 reviews)relatively inexpensive and quite reasonable image qualitycircular image only on full-frame cameras
This lens is great, given that the alternatrives are either a very expensive (even used) camera maker's lens or a relatively poor quality converter. Image quality is very high, though there is CA.reviewed January 15th, 2007
With this lens it is possible to produce an immersive VR image with only three exposuresif you have a full-frame camera, or with a few extras if you mount an APS-C sensor camera vertically; on those cameras the top and bottom edges are cut off but you can still cover the full circle with plenty of overlap with 6 images and could probably get by with fewer.
On an APS-C sensor camera you get the full 180 degrees horizontally, but less, I think about 120, vertically, and the top and bottom of the frame are cut off. Images can still be remapped quite effectively to very wide panoramics, or to very interesting ultrawide shots.
One thing to watch out for if you are looking for one of these lenses; the older version of the manual-focus Sigma 8mm only covers 170 degrees or thereabouts, and should be avoided if you are looking for easy immersive panorama shooting. Even that lens can produce some very interesting results, though--a sample image from that lens, remapped to rectilinear using Panorama Tools (with some subsequent editing of the pictures on the wall):