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Forum: Pentax SLR Lens Discussion
05-15-2011, 01:04 PM
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At infinity FOV is , in linear dimensions infinite and magnification is zero. This is true for all lenses. You are better measuring the field of view in terms of an angle
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Forum: Pentax SLR Lens Discussion
05-15-2011, 09:20 AM
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In theory, field of view is simply a function of focal length and image format so it would not change as a function of zoom over prime, however, and this is important to note. some zooms (specifically super zooms with high zoom ratios), and even some primes (most notibly ones with fixed rear element design but also some internally focused designs) only actually hold the true focal length at infinity focus. the reason is that focusing involves in these cases movement of the internal elements and changing to some extent the effective focal length of the lens when focusing closer than infinity.
Since by standards, the focal length is only tested for infinity, not many lenses have the change in focal length reported as a function of focus distance even in test results.
there have been some posts here in the past regarding this point.
Bokeh is a much different beast, and it changes from lens model to lens model even within primes, and is impacted by so many things, including the shape of the aperture blades when stopped down from wide open, and the placement of the blades within the lens grooup, as well as whether the lens is internally focused or not..... there is no simple rule
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