Tag : measuring the focal length of a telescope

Calculating the actual f/ ratio of a picture

Every telescope or telephoto lens has its “magic” f/number: that is, the ratio between its focal length and aperture. Although we don’t go deeper into the matter as it’s not within the scope of this article, it’s worth mentioning that the higher the f/ratio, the longer the exposure time required to yield a given picture density (i.e. how much detail we want to record). Each telephoto lens is normally used with the camera body it was built for, so that […]