أنواع العدسات ٢_a .. كتاب التصوير علم وفن

Photograph with a telephoto lens while holding it in the hand, unless the shutter speed is faster than the reciprocal focal length of the lens. For example, a lens with a focal length of 500 mm does not use a shutter speed of less than one second, and so on.

Monoculars & scopes: Telescopes can be installed on a single-lens reflex camera in two ways:

(a) The telescope is mounted directly on the camera body. (b) The telescope is mounted on a standard camera lens.

Catadioptric lenses: These are lenses that contain mirrors in their optical group. Lenses whose focal length ranges between 250 mm and 2000 mm for 35 cameras, and they are distinguished from their counterparts in focal length of regular telephoto lenses as follows:

(a) It is shorter in height, although it is more obese. (b) lighter weight. (C) Completely corrected for chromatic aberration.

Its disadvantage is that its pupillary aperture is fixed and does not change. If we want to reduce the amount of light passing through it, we can only do that by using density filters. Therefore, we cannot obtain a greater depth of field because it is not possible to narrow the aperture of the lens.

10- Aerial photography lenses: These are specialized lenses that are not suitable for any purpose other than what they were designed for, which is aerial scanning, to give their best sharpness at infinity, and when a dark red filter is installed on them.
11 - Zoom and varifocal lenses: These lenses were designed first for cinema cameras, then they were designed for single-lens reflex cameras, whether they are 110, 35, or

It is characterized by the ability to change the focal length in any ratio between two fixed limits. The zoom lens may be in a wide-angle range, such as 24mm-45mm, or in a range around the standard lens, such as 35mm-70mm, or in the range of telephoto lenses, 70-210mm. The production of this type of lens is advancing at an amazing speed, and now we see a company offering a 28mm-200mm zoom lens. Progress continues.

The most important characteristic of these lenses is the ease of use. In some types, we see that there are two rings, one for changing the focal length, and the other for adjusting the distance. An easier-to-use type has a single ring that pulls and pushes to change focal length and twists to change distances.

These lenses are characterized by the following:

(~~) (a) One lens replaces two or more lenses. You can adjust the exact frame of the shot and what the image contains without changing the location. This is very important for those who photograph reproductive films to make color slides, as they do not have the opportunity to crop the image (see Part Three, Chapter Two). (c) Gives a special effect when photographing while plowing the focal length

The defects of this type of lens are as follows:
(a) The lens is heavier in weight and larger in size than a monofocal lens (but if we take into account that it replaces more, it would be lighter in weight). lens from

(b) Less sharp as a single focal length (modern types are almost as sharp as single focal length lenses from

There were primitive types of this type called Varifocal lenses, which whenever you changed the focal length needed to reset the distance. Or, like the old zoom types, the pupillary aperture changed when the focal length changed. As for modern types, the aperture of the lens is adjusted so that its number remains constant when any change in the focal length occurs. Some modern species also include the ability to photograph objects.

Somewhat close.

12 - Supplementary lenses: These are similar to optical filters and are installed in front of the original lens of the camera. These lenses shorten the focal length of the lens so that they can shoot at a shorter distance and are usually found in sizes +1, +2, +3 or +4 diopters.

Diopter.

There is a variable zoom type between about +3 and +10 diopters.

It is preferable to use a narrow aperture lens with these complementary lenses due to its lack of efficiency in relation to the camera lens.

13- Additional slip-on lenses: These are lenses that are mounted on the front of the original lens to change the angle of view of the lens to a wide-angle or telephoto lens. And there are these lenses to be used together
Cameras with viewfinder that do not have the ability to change lenses or for dual-lens reflex cameras.

14- Teleconverters: These are additional lenses that are installed between the camera body and the original lens or telephoto lens. This leads to an increase in the focal length of the original lens by a special factor according to each converted lens. This coefficient is in the range of 1.4 to 3 but most of it is 2×.
And when installing a 2× converter lens, for example, between a camera and a lens, for example, 50 on a 35 camera, we find that the lens has become the tasks of a lens whose focal length is 100 mm 250, i.e. it has become a telephoto lens (long focal length) and it gives a shadow on the film twice the size of the previous one without a converter lens.

There is a type of convertible zoom lens whose focal length ranges between 2 and 3 ×. There is a type of close-up called Macroteleconveter that can photograph small objects up to size

equals the magnitude of the negative.

These lenses are for 35 cameras and some 120 cameras. The advantage of these lenses is that they are light in weight and cheap, and they can double the focal length of all the lenses you own. If you own a group with a 50mm, 135mm lens, after installing this converted lens, you also have 100mm, 270mm lenses, and so on.

Its disadvantages are:

(a) Less sharp than the original lens.

(b) Makes the pupillary aperture less by a factor. If the original lens was F/2.8 and a 2x adapter lens was installed, the maximum aperture would be 2.8 2-5.6. Thus, you get a longer lens at the expense of image sharpness and lens speed. .

15 - Tilt and shift lens: It is used to fix perspective, and only architectural photographers are charged with it.