Remember that focal length is stated for infinity and most lenses decrease in focal length as you focus closer.John Driessen (johnnie5) on August 21, 2020 in With the advent of digital cameras having non-standard sensor sizes there seems to be quite a lot of confusion concerning focal length, field of view and digital multipliers and how There are two types of lens you'll find in photographic use. rectangular map with horizontal and vertical straight lines representing latitude and longitude using a Mercator projection. The "digital multiplier" is 1.6x for most Canon consumer DSLRs, 1.3x for the EOS 1D, 1x for the EOS 1Ds, 1.5x for most Pentax, Nikon and Sony DSLRs and 2x for most Olympus DSLRs. Well the 1:1.5 ratio of vertical to horizontal if the APS-C sensor is changed when the image is "defished" and becomes closer to 1:1.7 Below is a calculator for FOV in both angular and linear terms. The corrected forumula is: Using the above information we can calculate, for example, the field of view of a full frame fisheye lens designed for 35mm use when used on an APS-C camera. Let's assume it uses equisolid angle projection, so the FOV is given by \begin{align}\text{AFOV} & = 2 \times \tan^{-1} \left( {\frac{50 \text{mm}}{2 \times 200 \text{mm}}} \right) \\ \text{AFOV} & = 14.25° \end{align} Calculating FOV Using a Lens with a Fixed Magnification. to "real world" coordinates.
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The illustrations above show the pinhole model of rectilinear and fisheye lenses.
Connie Cassinetto (Via the Lens) on August 11, 2020 in Probably the most common is the equisolid angle projection, and the FOV at infinity focus is given by:
There are two types of lens you'll find in photographic use. As the lens is focused at distances closer than infinity the field of view narrows, but unless you get into the macro range, the change is very small. Focal length is an optical attribute of a lens, which has nothing to do with the camera or the type of sensor it uses. The plot below shows how the field of view relates to frame size for a given focal length lens for a rectilinear lens and four types of fisheye lens. So again, FOV isn't determined by focal length, it's defined by focal length First let's define a few terms:
You can think of the various rectilinear and fisheye projections as being somewhat analogous to map projections. Here's the same plot on a log axis so you can better see how things change at short focus distance: It's pretty much the way our eyes see things and it's exactly the way a pinhole cameras sees things. If you "defish" a fisheye image,
However just like a rectilinear lens tends to stretch out objects at the edge, such a map projection stretches out areas near the poles. which different fisheye lens manufacturers have used. This one is extremely important to understand. Instead there are several different "mapping equations" or "projections" For those used to thinking in terms of 35mm cameras these would correspond to lenses with focal lengths of 20mm, 50mm and 300mm respectively. The field of view of a rectilinear lens focused at infinity is very easy to calculate using simple trigonometry. Lenses have an
C and D are equidistance and equisolid angle fisheyes respectively (most common) FOV and 43.25mm for the diagonal FOV.
real lenses a very large, very strongly curved negative front element must be used as shown in the lens diagrams below:
Also popular is the equidistance projection, and for the the field of view is given by: Canon give numbers of 142, 92 and 180 for their