The F-number of a photographic lens is a measure of its light-gathering ability, and is expressed as its aperture diameter ...

Though still only in the prototype stage, this flat lens could one day be used on space telescopes, and perhaps even on amateur telescopes.

This unique optical unit produces stunning video with a shallow depth of field even at fast apertures and is easier to focus ...

When it's small the depth of field is shallow or narrow. Focus distance The focus or focusing distance is the distance between the lens and the subject. You'll need to change the focusing distance ...