العدسات ٢_a .. كتاب التصوير علم وفن

But if you shoot the pictures so that the main subject in the picture is the same size on the film, the perspective will be different. This is not due to the difference in the angle of view due to the difference in the distance between the camera and the subject to be photographed. Therefore, the expression wide-angle perspective or telephoto lens perspective is a metaphor for what we will discuss later. So the difference in perspective is only due to the difference in the distance of photography

(b) Lens Speed:

It is that property that determines the maximum that the lens can allow to pass through. The fast lens has two advantages. First, high shutter speeds can be used. Secondly, it allows making the depth of the sharp region (depth of field) very shallow, thus increasing the effect of depth in the image. a light .. . This allows.

But everything has a flip side, the slower speed lens may be sharper and also cheaper. But currently there are 1.4 lenses that are comparable to any other lens.

Now, what is the meaning of this number 1,4, etc. that we see written on the lenses and on the lens's pupillary ring?

In short, it is the ratio of the focal length of the lens to the pupil diameter

If we assume that the focal length of the lens is 50 mm, and the diameter of the pupil at its maximum width is 25 mm, then the speed of this lens is: 2/F or 2:1 is written on the lens, and the smaller the pupil wide, the higher the number. 2 =
Focal length 50 hm

Two lights have the same focal length, but different pupils, and therefore their joy is different

12.5 For example, a pupil with a diameter of 12.5 mm is the speed of its lens. = 4 and so on. Currently, the maximum lens speed is 1.2 or 1.4, and it was manufactured by Leitz

Leica camera makers have a speed of 1. It was agreed between the lens makers that the following numbers should be used for lenses 1 - 1,4 - 2 - 2,8 - 4 - 5,6 - 8 - 11 - 16 - 22 - 32 - 64...etc.

pupillary ring -

Ring distances measure field work

THHE

lens and pupillary apertures

It is noted that each pupillary aperture that is larger in size (that is, smaller in number) allows the passage of twice the amount of light of the pupil that is smaller in size (larger in number) that follows it. For example, aperture 1.4 allows twice as much light to pass through as aperture 2, and aperture 8 allows twice as much light to pass as aperture 11.

And that's it

(C) Covering Power:

It is that property that determines the largest scale of the film with which a particular lens is suitable so that the light reaches all parts of the film and the image is sharp in the middle and the edges

This feature does not mean much to us at this level unless you use small camera lenses on a larger camera, as you may find that the coverage power is not enough. Also, when using a shift and tilt lens in architectural photography, you must make sure that it has sufficient coverage power

(d) mechanical aspects:

<-1 How to mount the lens on the camera: When you buy any new lens, you must make sure that this lens can be installed on your cameras, because until now, camera makers have not agreed on a unified way to mount lenses on the camera.
0 E

butt lock

Bayonet

Screws

Means of mounting the lens on the camera

In general, there are three main methods:

(a) Using screws such as old Practica and Pentax cameras and some current Russian Zenith cameras. This method is very slow and on its way out.

(B) By the so-called Breech lock, which is a ring around the hole designated to receive the lens in the camera or at the back of the camera. This method was used by Canon in its cameras and some other cameras such as the Pentacon 6.
(c) The current common method - even though almost every company has its own system - is the so-called Bayonet mount, which consists of protrusions at the back of the lens, which are inserted into special mounts in the camera and then the lens is wrapped around the lens, thus installing it in the camera. This is currently the best method because it allows all the information from the lens to be communicated to the camera and back until it becomes a camera.

The camera is fully automatic.

2 - Direction of focal distance adjustment: It is preferable to buy different lenses so that the direction of adjusting the distance is all in one direction so that you can

Work quickly.

- Automatic work: some lenses have an “A” mark on them when you want to work automatically with the camera, and move from this mark to the number of pupils if you want to work manually.

4 Automatic distance adjustment: There are currently some lenses that work on some cameras that adjust the distance automatically, such as what Canon and Minolta produced to work on some of their cameras.