Canon D30 With EF 15mm Fisheye
Rico Tudor
Like most DSLRs, the D30 makes life difficult for wide-angle users. The 1.6 multiplier turns the attractive 24mm into a 38mm. I seriously considered the following lenses:
Canon EF 16-35mm f/2.8L zoom Canon EF 14mm f/2.8L Sigma 14mm f/2.8The 16-35 is heavy, large and expensive -- and I just want the 16mm part. The Canon 14mm is heavy, large, and astonishingly expensive. The Sigma 14mm is heavy, large, and subject to variable build quality; I did like the price, and was close to buying.
However...
After viewing some samples of the Canon EF 15mm f/2.8 fisheye, before and after processing by Panorama Tools, I began to see another way out. So I bought one (shameless plug for Delta International here).
Technical recap of wide-angle lenses:
A rectilinear lens will preserve the straightness of lines throughout the frame, but objects at the edge become stretched, losing their proportion. These lenses are desirable for architecture. For normal appearances, keep people away from the edges.The Canon EF 15mm is fairly light, fairly small, and decently priced. (The Sigma fisheye is even cheaper, but I demur.) So, the trick is to use software to unbend the lines for those cases when you want rectilinear behaviour from your fisheye lens.An angular fisheye preserves the angle between two lines, but lines become increasingly curved at the edge of the frame. Subjects with recognized proportions, like people, will look best with this lens. For normal results, keep straight lines away from the edges.
I have calculated the angle of view (in degrees), with camera in landscape orientation:
| 14mm rect 14mm rect 15mm fish 15mm fish 15mm fish axis | full frame D30 frame full frame D30 frame D30 frame | linearized ---------+----------- --------- ---------- --------- ---------- diagonal | 114 88 180 113 104 width | 104 78 150 94 94 height | 81 56 100 62 62 ¤ ¤ Confirmed at my optical bench (desk, ruler, pencil, paper) :-)You can check my working with some knowledge of right-angle triangles, and these givens: Canon EF 14mm has rectilinear design, EF 15mm has angular fisheye design, D30 has 1.6 linear multiplier for the sensor vs 35mm full frame.
The table shows 14mm rectilinear beaten by the 15mm (in fisheye or rectilinear mode). In rectilinear use, the fisheye lens requires cropping: this reduces original pixel data and reduces resolution. These losses are minor, and occur in the corner only.
Key observation: The Canon EF 15mm fisheye, used with a D30, linearized, and cropped to full frame, is equivalent to a 10.6mm rectilinear lens!
Flash issues arise with this extreme coverage. From the D30 manual: "Covers field equivalent to a focal length of 18mm". While ambiguous, it sounds impressive... or maybe not. Being charitable, I get 100° diagonal coverage, which is not quite enough for linearized pics, and entirely inadequate for fisheye. I tested coverage of the built-in flash and the Canon 550EX external flash.
In summary, the D30 and fisheye were made for each other. Versus the 14mm rectilinear, you get the following: better price, super-wide coverage, lower weight, smaller size, no light fall-off, sharper corners.
Links:
Panorama Tools by Helmut Dersch is open-source software to perform sophisticated geometric transformations on your images.P.S. I have my own software to perform image linearization and interpolation, fed by Dave Coffin's CRW decoder (way cool). The interpolation uses sinc() with a Lanczos window, operating directly on the Bayer data. I want to release the source, but I'm bogged down with color problems. Soon.
AcaPixus has good samples of de-fished images.
Dave Coffin has open-source software to decode Canon raw images (CRW files)
Paul Bourke describes the angular fisheye projection.
Photo gallery follows...
At the restaurant, a fisheye captures the scene without my standing on the next table. Distortion of the pillar is minimized by placing it near the center of the frame. The table, being round, is unfazed by circular distortion. With the wide angle comes generous depth-of-field and longer exposures hand-held.
