New answers tagged lens-design
The answers above are correct but another way of looking at it is as mentioned: all lenses create a circular image. Most are designed so that the diameter of the image circle is greater than the diagonal of the sensor otherwise you are not filling the whole sensor. Now fish eye lenses are designed to cover 180 degrees in all directions so to make the whole ...
All lenses create a circular image, it's just that most of them have an image circle large enough that it covers the entire sensor. Vignetting at wide apertures is a manifestation of the image circle encroaching on the corners of the sensor as the circle edge is not as sharp as it would be with a narrower aperture. With a fish-eye lens, the image circle is ...
Consider this review of the Canon 8-15 f/4L USM fisheye, which can shift from circular at 8mm to diagonal at 15mm. Yes, it's circular because the lens's entire image circle is inside the area of the sensor, rather than covering the entire sensor. I'm not sure there's going to be an entire explanatory webpage other than Wikipedia on this, because it's such a ...
Macro lenses will usually stay at a fixed focal length because A) it is difficult to focus with zoom changing B) Zoom lenses can present stability issues when close to a subject There are a few macro lenses that the photographer can "lock" at the minimum focal length.
Top 50 recent answers are included