New answers tagged focal-length
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Why is aperture expressed as a function of focal length and not in absolute size?
Because that way you don't have to keep doing math for every lens you use. A given aperture diameter lets in different amounts of light for different focal lengths.
f/2 (where f is focal_length) lets ...
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Why do telephoto lenses have long focal length?
Ironically enough, a 10 mm or 20 mm lens (on a full frame or crop sensor DSLR body) sort of is a telephoto lens, in the sense that it has be a retrofocus lens (in order to not intrude in the mirror ...
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Why is aperture expressed as a function of focal length and not in absolute size?
There are already a lot of great answers on here, but perhaps a simple addition I would like to add is that the f-number is in theory, as already mentioned, just a ratio of = focal length/diameter of ...
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Why is aperture expressed as a function of focal length and not in absolute size?
What is important for determining exposure is the amount of light per unit area on the sensor. For a given object and aperture absolute size, a larger focal length lens will produce a larger image ...
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Why is aperture expressed as a function of focal length and not in absolute size?
My explanation in simpler terms.
Because it is actually a relationship, not an absolute size.
Any division is a relationship between the top number and the bottom one.
When defining the aperture we ...
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Why is aperture expressed as a function of focal length and not in absolute size?
The brightness of the image is proportional to the amount of light admitted by the lens. We are interested in quantifying image brightness because we will use this value to determine what settings are ...
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Why do telephoto lenses have long focal length?
Put simply, every time you bend light it reduces the potential IQ; every lens element, aperture restriction, etc... there are definite negatives to making a lens more complicated than necessary; ...
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Why do telephoto lenses have long focal length?
Law of physics
In the image above, assume that the "object" is sufficiently far way from the camera so that the distance between the sensor plane where the "Image" is projected ...
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Why do telephoto lenses have long focal length?
Let's put it the other way round:
If you were to construct a lens for a desired focal length, under which circumstances would you use a telephoto lens construction?
To make it concrete, let's talk ...
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Why do telephoto lenses have long focal length?
Let us say we want a focal length of 10mm.
In order to be "shorter than its focal length", our lens design needs to be shorter than 10mm and still be large enough to illuminate our sensor. ...
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