The focal length differs with the thickness of the lens
Smaller sensors 'crop' the scene and make a lens appear to have a longer focal length.
Or, you can calculate the exit pupil by dividing the focal length of the eyepiece (in mm) by the focal ratio of the telescope.
consists of a number of small lenses arranged to make a lightweight lens of large diameter and short focal length.
F-number: The figures marked on the lens collar to indicate the size of the lens aperture in relation to its focal length.It is the ratio of the aperture diameter to the focal length of the lens.
The automatic adjustment in the focal length of the lens of the eye to permit retinal focus of images of objects at varying distances.
If you like taking photos of birds or other wildlife, or if you’re just a peeping Tom, you can get a superzoom camera with a built-in lens with an insane focal length.
equivalent focal length
short focal length (high aperture) lens
This dissertation aims at meeting the needs of designing long focal length space camera.
The results indicate that with the increase of focal length, the intensity distribution on the focal plane varies from central-dip form to Gaussian distribution.
The ratio of the focal length of a lens or lens system to the effective diameter of its aperture.
For example, a telescope with a focal length of 2000mm has twice the power and half the field of view of a 1000mm telescope.
Having three focal lengths.
variable focal length (cylindrical) lens
They have a focal length, and where an image is formed depends on a combination of the focal length and the distance between the object and the lens.
The focal length of camera is estimated efficiently by using the algorithm of equidistant matching, images are warped to the surface of sphere whose radius equals to the focal length of camera.
The aperture size (area of the aperture) of a lens could be calculated from focal length and the correspondent f-number.
How deep I should distort the building shapes by using wide angle focal length or if I should avoid it and use more close to standard values or even a telelens.
Set the focal length on your lens.
The unsteadiness of air becomes prohibitive only if instruments with large focal length are used.
a camera lens having a wider than normal angle of view (and usually a short focal length).
A focal length only half the diagonal of the film frame, produced with an almost symmetric lens design of surprising compactness, featuring the typical advantages of symmetrical lens designs: distortion is extremely well controlled, and so is color correction and image field flatness.
Further study on thin-lens focal length measurement experiment;
Electrically driving and controlling adaptive 128 element×128 element liquid crystal micro-lens array with tunable focal length
As a result, the focal lengths in these planes will be different.
Measurement of optical surface and foci of long focal length lens by CGH
The creative point of the paper is that the distribution of the temperature inside the laser crystal and the thermal focal length with Gauss pump source in 4-order approximation were deduced.
Once you choose a lens whose focal length is closest to the focal length required by your imaging system, you need to adjust the working distance to get object under inspection in focus.
Sturdy of large-diameter,long focal length collimator assemble technical
拉開窗簾，那撲面而來的光亮，使我想到了人類的早晨。
the ratio of the focal length to the diameter of a (camera) lens system.
In his view, such a distraction when shooting do not have to adjust the focal length, the results can determine whether the visual frame by which the camera.
A unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length measured in meters.
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