Lens mount developed by Nikon, typical used for line scan cameras
Most distant point on the optical axis with an image of “acceptable sharpness”
Alternatively, we can express the FarPoint using the magnification M :
A 5 Mega lens with f=7.2mm focal length and F-stop F2.4, focused to an object distance of 100mm then has a far point of
und einen Nahpunkt von
A 5 Mega lens with f=7.2mm focal length and F-stop F2.4, focussed to 100mm then results in
und einen Nahpunkt von
thus we get
see also http://www.optowiki.info/blog/can-i-increase-the-dof-by-changing-the-focal-length/
(usually horizontal) extend of an object that’s visible on a sensor.
Sometimes the HFOV (horizontal field of view), sometimes the VFOV (Vertical Field of View) and sometimes the DFOV (Diagonal Field of View) matters. It’s of utmost importance to state clearly which matters.
Various types of fisheye lenses are available.
Here a short overview:
|lens class||wide angle||Fisheye||Fisheye||Fisheye||Fisheye|
|maintaines||-||angles||angular distances||areas||planar illuminance|
Source of the various angles: wikipedia
F-Theta lenses are also called “equidistant“, “linear scaled“, “äquidistant” or “angular”
sterographic lenses are also called “ conform“or “ winkeltreu”
orthographic lenses are also called” hemispherical“or “orthographisch”
The focal length is the distance from the Image side principal plane to the image of objects at infinity.
Note that this is a positive value for converging lenses and a negative value for the divergent lenses.
The larger the focal length, the smaller the aperture angle of the lens and the smaller the object section that is displayed full-frame on the sensor.
The lens captures less of the object. Extremea are telephoto lenses and finally telescopes.
The smaller the focal length, the larger the aperture angle of the lens and the larger the object section which is displayed full-frame on the sensor.
The lens captures more of the object. Extreme forms are fisheye lenses.
Lenses are typically listed, sorted by focal length. As an approximation, lenses with larger focal length see a smaller portion of the object (in more detail).
There are exceptions! (See: pseudo-knowledge: viewing angle and focal length are equivalent)
However, Viewing angles change with the working distance! Also, a Pinhole lens model is assumed. Thus for wide angles a too small focal length is returned .. (as all focal length calculators on the internet do 😉 )
For the next calculator it is very important to correct the distortions before doing the calculation:
When a ray of light is sent parallel to the optical axis into a lens or lens system, then the ray or it’s prolongation intersects the optical axis after exiting the last lens.
This intersection with the optical axis is called focal point.
The name is derived from “burning glasses” (imagine a magnifying glass) with which the (nearly parallel) sun beams are bundled to one point.
At this point it gets so hot that wood or paper placed at this spot starts to burn.