Summary. The 15mm fisheye allows significantly greater
angle-of-view than a 14mm rectilinear. The angle is
so wide that flash coverage requires special attention.
With computer software, the fisheye view can be changed
to rectilinear, if desired.
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
Canon EF 16-35mm f/2.8L zoom
Canon EF 14mm f/2.8L
Sigma 14mm f/2.8
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.
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).
recap of wide-angle lenses:
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.
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.
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.
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
---------+----------- --------- ---------- --------- ----------
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) :-)
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
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.
observation: The Canon EF 15mm fisheye, used with
a D30, linearized, and cropped to full frame, is equivalent
to a 10.6mm rectilinear lens!
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
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.
by Helmut Dersch is open-source software to perform
sophisticated geometric transformations on your images.
has good samples of de-fished images.
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.
f/4.5, 1/15 sec, ISO 800,
rare case when DOF is exceeded (bokeh is not so
good). Our Penny is five inches from the lens. Notice
the strong fisheye curvature affecting her whiskers...
just kidding! The fisheye is not responsible for
her exaggerated body proportions: the effect is
caused by her proximity, and would occur with a
f/4, 1/45 sec, ISO 100
After PanoTools, cropping back
to a full-frame image will necessarily lose
a little pixel data (and resolution), but
only in the corners.