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Why should we match each type of frame field to its function. (not all options are used)? 

Match each type of frame field to its function. (not all options are used.) is a scientific topic. Suppose a lens has an aperture opening that is too wide and allows the light to come in, which you can control by the adjustable aperture blades. The wider the aperture opening, the less sharp will be the picture produced by this lens because more light from different sources will be allowed to enter it. Therefore, if we are using such a lens for photography and are aiming for as sharp a picture as possible, we need to use a smaller aperture opening so that less light will come in. 

The aperture opening of the lens may range from large to small. It is typically represented as in the units of f-number (f/1, f/2, f/4, etc.). The smaller the number means that the opening is larger. This means that less light will come in and therefore you will get a sharper image. Make sure that you understand the relationship between aperture and depth of field (the minium distance between closest and furthest points of acceptable focus). Also be aware that with smaller apertures, less light comes into the camera.

What is the use?

Here is another example. The lens which you may use to shoot a movie. And I would like you to correct the position of aperture blades so that it gives as close to cinema-like image as possible (close focus, or also known as hyperfocal distance). You see, when shooting a movie, you should shoot from the place where there is enough space between the actors and the audience. But if an ordinary lens has an aperture opening which is too small for shooting a movie, it will not be able to give wide angle view towards front and/or back of an audience. This can lead to problems such as camera shake or less sharpness in such places.

What are the features?

The aperture opening of the lens is what controls the amount of light that enters it. The size of the opening is determined by two factors: the focal length of the lens and the f-number.

1) When you change focal length, it affects depth of field, so that more or less space will be in focus. But it does not affect aperture size.

2) When you change f-number, it affects the light coming into the lens, so that more or less light will reach camera’s sensor. But it does not affect depth of field. As we all know, larger f-number means smaller opening and less light comes into a camera and vice versa. We have learned that if we want to get as large depth of field as possible , we need to use a long focal length lens with a large aperture setting.

Some more facts:

“The governing factor represents what we want to indicate with a unit number, i.e., how much we want to change an F-number in order to obtain a certain change in image quality.” The numerical factor represents “how much we are willing to sacrifice a f-number value”, when our intent is to obtain an improved picture. In general, narrower the numerical value (i.e. greater margin), the better image quality we will obtain.

By selecting the “f-number” option, we can select which aperture (and f-number) will be used by the camera; so that it can be set, for example, to a larger value when photographing in low light conditions. When the camera is set to a large aperture value, more light is allowed into it, and less light is allowed out through the shutter. In a similar way, when the camera is set to a small aperture value, less light is allowed into it and more light is allowed out through the shutter.

On the other hand, by selecting the “aperture” option, we can change the f-number after we adjust the shutter speed. For example, if you are in a dark room and need more light to be able to photograph a subject with that aperture setting at normal exposure time. You could select high ISO sensitivity (higher numerical value of ISO) so that a high shutter speed (lower numerical value of shutter speed) can be used while maintaining that small aperture setting.

What are the benefits?

When we shoot a wide-angle image, we may want to decrease the angle of view and therefore increase the depth of field. However, making images with a narrow aperture does not give us that latitude for controlling depth of field, as it does with us in terms of modifying focal length. This is because changing a value increases or decreases the lens opening size by a factor that is actually independent from the f-number. For example: If you use an F/2.8 lens, and you want to decrease the angle of view to increase depth of field, you can change its focal length without having to change its aperture. 

That is because changing a focal length by a factor of 2.8 will not affect the lens opening diameter by the same factor. It actually has this effect: it will have twice as much light coming in (this is the F/2.8 value). 


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