العدسات ١_a .. كتاب التصوير علم وفن

Chapter Two: Lenses

Lenses, as you know from the lessons of nature, are: those glass objects (or any transparent material) that collect or scatter rays.

Without entering into scientific details that are of interest only to specialists, we will focus our research on aspects of interest to the photographer:

First: the properties of the lenses

There are four properties that determine what the lens can and cannot do. .

(a) Focal Length:

It is the distance between the optical center of the lens (usually inside the lens) and the surface of the film. And it is written on the lens like this = 50mm, and it affects two important things: Image Size: i.e. the length of the image on the film 1- Size

We note that the image size is directly proportional to the focal length. For example, if a lens with a focal length of 50 mm at a certain distance gives an image of length 2 cm on film, then a lens with a focal length of 100 mm at the same distance gives an image of length 2 cm on film.

small picture

Long focal length

Focal length relation to image size

2- Angle of View:

The lenses differ in the area that you see, which is what was agreed to be called the angle of view. While the 50mm lens of the camera sees a 35 angle of view of about 45, we find that
The 300 nm lens, for example, has an angle of view of about 8. As for the fisheye lens, whose focal length ranges from 8 nm to 6 nm, the angle of view is about 180.
angle of view of some lenses

We note here that the normal lens for a 35 camera is 50 mm, and for a lenght camera

Its film is 120 (6) 6 is 80 mm, which is approximately the length of the negative's diameter. This length has been agreed upon because the view seen by this lens gives a perspective close to what the human eye sees clearly (the eye receives the rays from an angle of about 180, but it clearly perceives what its angle is about) 50) We find that the difference in the angle of view does not affect the perspective if all the images are photographed from the same distance with different lenses.