Diffractiongrating

In the earlier days,  rotating lens focal length calculators made out of paper were good and simple tools for quick calculation of the field of view. As well as the formula above. But you should not use this formula for modern wide angle cameras!

diffraction翻译

Alternatively, if the two waves coincide and interact in a way such that the trough of one wave coincides with the peak of the other (in an out of phase manner), the resultant wave will display a much lower amplitude. This is known as destructive interference.

Fraunhoferdiffraction

The bright-line is produced at the center of the screen as the two waves travel an equal distance to reach this point and interfere constructively. When the two waves travel the small distance away from the center in either direction, they travel slightly different distances. They are out of phase. When the difference in their traveled distances is exactly one half of the wavelength,   they meet by producing destructive interference. The dark regions correspond to regions where the peaks for the wave from one slit happen to coincide with the troughs for the wave from the other slit (destructive interference), while the brightest regions correspond to the regions where the peaks for the two waves (or their two troughs) happen to coincide (constructive interference). The diffraction pattern is an inherent property of waves and presents compelling evidence for the wave nature of light.

Waves also show a characteristic behavior called diffraction. When a beam of light passes through a slit with a size comparable to the wavelength of the incident beam － the beam bends (or diffracts) around the slit. On the contrary, when a stream of particles is passed through a slit, the particles simply come out through the aperture.

Traditional calculators cannot calculate focal length for modern wide video surveillance cameras. Modern security cameras with short lenses (2.1 – 2.8mm) have non-standard wide angles. For example 115 degrees.

Fresneldiffraction

We also offer much more sophisticated CAD software for CCTV design, like our IP Video System Design Tool, that has a built-in database of more than 9000 camera models.

Reflection, refractiondiffraction

Lens Focal Length = (Distance) * 3.2 mm / HorizontalWidth where 3.2 mm is the horizontal size of 1/4″ CCTV sensor (4.8 mm for 1/3″ sensor).

Single slitdiffraction

The standard formula above doesn’t work for such lenses. You need to have a database of camera models with horizontal and vertical angles provided by camera manufacturers.

Further, when a beam of light passes through a pair of closely spaced slits separated by a distance comparable to the wavelength of light, circular waves are produced at each slit by the process of diffraction. These two waves interfere with each other such that an interference pattern with alternate dark and bright lines is obtained on a screen placed at a short distance behind the slits.

We created the unique FREE lens focal length calculator that has a database of camera models and shows correct angles and DORI zones with 3D graphics:

Interference is a characteristic phenomenon exhibited by waves. When two electromagnetic waves interact with their peaks and troughs coinciding, a resulting wave with enhanced amplitude is produced. This is known as constructive interference. In this case, the two waves interacting are in phase with each other.

Apart from the lens focal length calculator function this software has 3D engine for automatic design and visualization of all elements of video surveillance systems.

When rays of light pass through a convex lens (the shape of lens shown in figure above) they tend to converge at a single point at some distance ahead of the lens. This distance between the lens and the point where they focus is known as the focal length as specified by the symbol f in the figure. In case of a CCTV camera, the lens focuses the rays at a point where the sensor is placed. The combination of the focal length of the lens and the size of the sensor determine the field of view of the CCTV camera. The shorter the focal length, the wider the field of view, and vice versa.