tvagi
Established
hi everyone.
i have a question about the f-stops.
i realize that a small f determine how fast a lens is
but what about the big f?
why some lenses have a maximum f-16(industar 61) and some others f-22(industar 26m)?
how does this affect pictures and is this important as the small f when choosing a lens?
i have a question about the f-stops.
i realize that a small f determine how fast a lens is
but what about the big f?
why some lenses have a maximum f-16(industar 61) and some others f-22(industar 26m)?
how does this affect pictures and is this important as the small f when choosing a lens?
FPjohn
Well-known
bmattock
Veteran
The function of an aperture (rated in f-stops) is to restrict or allow light to enter the lens. It works in combination with shutter speed and film or sensor ISO speed to influence overall exposure.
It can also be used creatively. A larger f-stop (smaller number) admits more light, allowing faster shutter speeds at low light, to reduce blur. It also has the effect of having less depth-of-field, which can create a dramatic effect of selective focus (such as portraits where the background is out of focus).
A smaller f-stop (larger number) admits less light, but it increases the depth-of-field, so more of the scene from front-to-back is in acceptable focus. The smaller the f-stop, the deeper the depth-of-field. This can be used creatively too, for example by allowing deep depth-of-focus for landscape shots.
Most lens designs have a limit to the smallness of the f-stop, beyond which an undesirable side-effect known as 'diffraction' can occur, which makes the image much worse. So you don't generally see f/64 on a lens for a 35mm camera, for example - it would be worthless.
When a lens stops at f/22 or f/16, it generally means that the manufacturer was unable to take it farther without incurring diffraction. It is a function of the lens design, not an indicator of quality.
Most lenses have a 'sweet spot' where they produce their best results, which tends to vary between f/5.6 and f/8 anyway. f/16 or f/22 are generally only needed in unusual circumstances.