Re: Field Of View Question


"Blour" <youzpalang@xxxxxxxxxxxx> wrote in message
news:1185462494.467879.129030@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

What if the Object is not at infinty, in this case what is FOV in
object space if we know the detector size and EFL (and the optics is
not a thin lens or optic)?


In this case one needs to specify more than the EFL. Use the thick lens
model, and assume both object and image spaces are in air (for simplicity).
Then the field of view is given by the nodal ray, that is for instance, a
ray that leaves the edge of the detector and passes through the nodal point
associated with the focal point on the image side of the system. (The nodal
point is the intersection of the principal plane with the optical axis.)

This backwards propagating nodal ray leaves the system (heading toward the
object) from the object side nodal point of the system and it has the same
angle with respect the optical axis as did the ray entering the system.
Thus the field of view of the system is the inverse tangent of half the
detector width divided by the image distance, where the image distance is
the distance between the image side principal plane of the system and the
detector. [The corresonding object point is then located at the usual, as
normally calculated, distance from the object side principal plane of the
system.]

Note that it is not necessary that the nodal ray actually be transmitted
through the system; whether it is transmitted or not depends on where the
stop is. The chief ray, on the other hand, is the ray that passes through
the center of the stop. The angle of the chief ray is the same as the field
of view only if the stop is located at one of the principal planes of the
system.

I say things like "the nodal point associated with the focal point on the
image side of the system" because it is possible for the nodal points and
principal planes to be crossed, that is, for instance, the object side
principal plane could actually lie physically closer to the image than does
the image side principal plane.


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