Atricle contents: difference between wide-angle lenses and fisheyes, fisheye and its focal length, Canon’s fisheyes comparison
What is fisheye lenses?
There are two major types of wide-angle lenses: simply “wide-angle” and “fisheye”. Actually fisheye lens is a subset of wide-angle lenses – because their angle is wide (and it is always much wider than simply wide-angle lenses).
Wide-angle or fisheye?
The difference is that the wide-angle lenses trying to manufacture with corrected distortion as much as possible (and the quality of wide-angle lens can actually be measured in its distortion: less distortion – better wide-angle lens). At the same time fisheye lenses especially manufactured with loads of distortion to make it possible to squeez lots of space into one photographic frame.
The result can be compared in the image below (the lower picture was pulled from the upper original picture):
Fisheye vs wide-angle images
Let’s collect the differences into one table:
|Parameter||Wide-angle lens||Fisheye lens|
|Amount of space||Limited by the frame (you can see that the columns bottoms are cutted off)||More details in smaller frame (the bottoms of the all columns appears)|
|Lines strightness||Stright objects appears to be stright on the image||Initially stright objects bent to arches|
|Object shape distortion||Objects near the frame coners unusually stretched (look at the tree branch top-right)||Objects looks about the same in any part of the image (for example all the parts of the fance look about the same as they are)|
Fisheye viewing angle
Only fisheye lenses can have the angle of 180 deg. and even more.
Wide-angle lens will never be close to 180 deg. viewing angle due to the phisical princip: all raytraces have to have the same angles on the entering and exit of the lens and as the sensor is flat – the space apearing on the image have to be a bit in front of the lens. At the same time the ray of light can get into fisheye lense stright from left or even a bit from behind and go in the sensor direction after the lens.
Focal length of fisheye lenses
Actually the focal length for fisheye lens is a virtual thing. Because if fisheye would have specified focal length at any setting and any part of the image – it would be ordinary wide-angle lens.
The main thing is that the specified focal length of fisheye lens can be aplied only to the very center of the image. In other parts of image focal length will be shorter.
For more details take Wikipedia in your hands and read: Fisheye mapping function at Wikipedia
Fisheyes from Canon
There are only two lenses in the current production line of Canon:
|Model name||Lowest actual price||Manufacturing period||Type||Viewing angle||Comment|
|EF 8-15mm fisheye||$1 299,00||2010-p.t.||Circular at 8mm to Rectangular at 15mm (on full-frame)||up to 180 deg. even on APS-H (Canon 1D)||Very sharp (even at corners) for fisheye|
|EF 15mm fisheye||No price||1987-2011||Rectangular||180 deg. diagonal||Sharp even wide-open|