Numpty question!
- Thread starter AndyWest
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Which is actually making the hole the light passes through smaller, hence stopping, (or closing, if you prefer) it down..
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A 'stop' as in Waterhouse stop was originally a metal plate with a hole in it, used to stop the light, and only allow a certain amount to pass.
To 'stop down' is a slang term for reducing the size of the hole, to a smaller aperture, ie a higher f/number.
The terminology used for lens apertures is old and confusing and often mixed up - you stop down to a higher f/number, which is a smaller aperture, which is a slow aperture. And that is the oppposite of a fast f/number, or a wider aperture, and so on.
Not very helpful, is it
Brighter and darker are pretty unambiguous terms, but hardly anybody uses them.
The same can be said of shutter speeds - higher and lower, faster and slower etc. Should really be shorter and longer :shrug:
To 'stop down' is a slang term for reducing the size of the hole, to a smaller aperture, ie a higher f/number.
The terminology used for lens apertures is old and confusing and often mixed up - you stop down to a higher f/number, which is a smaller aperture, which is a slow aperture. And that is the oppposite of a fast f/number, or a wider aperture, and so on.
Not very helpful, is it
Brighter and darker are pretty unambiguous terms, but hardly anybody uses them.The same can be said of shutter speeds - higher and lower, faster and slower etc. Should really be shorter and longer :shrug:
CT
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As Hoppy says, the expression dates back to those metal plates with varying size holes in them which preceeded automatic diaphragms, and those early photographers thought of it as 'stopping' light - hence the expression.
Nowadays the expression has become entrenched in exposure 'speak', so while it originally referred to altering the exposure by adjusting the aperture, we talk of decreasing or increasing exposure by one stop regardless of whether we do it by altering the aperture or the shutter speed. Put another way 'one stop' has come to mean a doubling or halving of exposure regardless of how we achieve it.
Nowadays the expression has become entrenched in exposure 'speak', so while it originally referred to altering the exposure by adjusting the aperture, we talk of decreasing or increasing exposure by one stop regardless of whether we do it by altering the aperture or the shutter speed. Put another way 'one stop' has come to mean a doubling or halving of exposure regardless of how we achieve it.
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And how are these numbers derived?
An f number is effectively a ratio.
that is the ratio of the aperture (whatever it is) to the focal length of the lens.
Take a 50mm lens. If you select f4 you are adjusting the hole to a diameter which will divide exactly into the focal length 4 times, That means that the actual diameter of the aperture would be 50mm /4 = 12.5mm
on a 200mm lens an f4 aperture would be 200mm /4 = 50mm in diameter
Which explains why long lenses with big maximum apertures have prices which rise exponentially (well not literally) There is a lot of vey costly and heavy glass in a 300mm f2.8 lens for example (aperture diameter = 300/2.8 = 107mm)
The Canon 300mm f2.8 has an overall diameter of 128mm to accomodate the large size of the object lens and costs over £3K
An f number is effectively a ratio.
that is the ratio of the aperture (whatever it is) to the focal length of the lens.
Take a 50mm lens. If you select f4 you are adjusting the hole to a diameter which will divide exactly into the focal length 4 times, That means that the actual diameter of the aperture would be 50mm /4 = 12.5mm
on a 200mm lens an f4 aperture would be 200mm /4 = 50mm in diameter
Which explains why long lenses with big maximum apertures have prices which rise exponentially (well not literally) There is a lot of vey costly and heavy glass in a 300mm f2.8 lens for example (aperture diameter = 300/2.8 = 107mm)
The Canon 300mm f2.8 has an overall diameter of 128mm to accomodate the large size of the object lens and costs over £3K
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A 'stop' as in Waterhouse stop was originally a metal plate with a hole in it, used to stop the light, and only allow a certain amount to pass.
To 'stop down' is a slang term for reducing the size of the hole, to a smaller aperture, ie a higher f/number.
The terminology used for lens apertures is old and confusing and often mixed up - you stop down to a higher f/number, which is a smaller aperture, which is a slow aperture. And that is the oppposite of a fast f/number, or a wider aperture, and so on.
Not very helpful, is it
The same can be said of shutter speeds - higher and lower, faster and slower etc. Should really be shorter and longer :shrug:
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