## How is focal length calculated?

The typical focal length formula looks as follows: 1/Focal length = 1/Image distance + 1/Object distance , where: Image distance and Object distance are given in mm.

## What is mm in focal length?

The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus, usually stated in millimeters (e.g., 28 mm, 50 mm, or 100 mm). In the case of zoom lenses, both the minimum and maximum focal lengths are stated, for example 18–55 mm.

**What is 200mm focal length?**

A 200mm lens is in the category of lenses called “fixed focal length” or “prime”, which cannot zoom in and out. The more common lens type is the zoom, which does allow you to zoom in and out.

### What is the formula for optics?

Optics Formulas

Total internal refraction | n 1 n 2 = s i n r s i n i |
---|---|

Critical angle, Ө | s i n Θ = n 2 n 1 |

Prism formula | μ = s i n A + δ m 2 s i n A 2 |

Len’s maker formula | 1 f = ( μ − 1 ) ( 1 R 1 − 1 R 2 ) |

### How do you read lens mm?

Focal length is expressed in mm and a higher number means a bigger zoom, while a lower number mean the lens can be used for wider shots. As a rough reference, the human eye is said to see about the equivalent of 30-50 mm on a full frame camera (more on that later).

**How far is a 300mm zoom?**

The bottom line – on a crop frame camera a 70-300mm zoom (Canon, Nikon, Sony) will get you pretty good coverage from 15 yards to 56 yards away, the ‘sweet spot’ for outdoor sports.

## What is 300mm zoom?

At 300mm the lens will have the equivalence of a 450mm lens on a 35mm film camera or Nikon FX (Full Frame) digital camera. Many P&S cameras will say they have a 8x or 12x zoom, that just means that the longest focal length is 8x or 12x longer than the widest focal length.

## How do you calculate the optical power of a lens?

The diopter is the unit of measure for the refractive power of a lens. The power of a lens is defined as the reciprocal of its focal length in meters, or D = 1/f, where D is the power in diopters and f is the focal length in meters. Lens surface power can be found with the index of refraction and radius of curvature.

**What are the formulas of light?**

Like all other electromagnetic waves, it obeys the equation c = fλ, where c = 3 × 108 m/s is the speed of light in vacuum, f is the frequency of the electromagnetic waves, and λ is its wavelength.