### 6. Field of View

 Written by Scott SparroldSmall Angle Field of View (FOV)The field of view of an optical system is the image height, d, divided by the effective focal length, EFL:Units are in radians. It is an approximation valid for small angles assuming tan θ ≈  θ.Actually I do not like the simple term "field of view". It causes a lot of confusion: is this "full field of view" (FFOV) or "half field of view" (HFOV). I therefore counsel that one never use the loose term "Field of view", but be more specific and say HFOV or FFOV.Exact Field for Large AnglesA detector array can be square or rectangular. For purposes of calculating total field of an optical system, one usually quotes the compound angle to the corner of the detector. One could model an angle with an X and a Y component but it is easier to model in the Y direction only (At least I only model a Y direction and I am LAZY!)Some large scanned systems require a field that is linear with image height. These are called Fq lenses, as opposed to traditional Ftanq systemsExample of exact Field of View:A 2/3" detector array has is 8.8x6.6 mm (link showing detector formats). A 25 mm, 5 mega pixel lens. What is the Full Field of View (FFOV)?Approximation:Exact:Instantaneous Field of View (IFOV) is the field for an individual detector element and is usually specified in milliradians (mr)