Of course, the pro-model standard zoom, now typically a 24-70mm, is a far better lens than its previous incarnations, with outstanding optical quality across its focal length
range, including the 50mm setting.
The lenses are available in 21 models with focal lengths
of 4mm, 6mm or 12mm and feature working distances that are very short or zero.
Because I had no other choice of focal length
, I researched and tried to learn everything I could about focal length
The time-honored solution to this ergonomie difficulty is to combine an eyepiece of moderately long focal length
(and thus comfortable eye relief and an eye lens of reasonable diameter) with a Barlow lens or other image amplifier that doubles or triples the magnification.
With a wide-angle focal length
of 6.5mm, the UA2.7x5.5 can also be used to provide a full view of a concert venue during live coverage.
The new CJ20ex7.8B includes a built-in 2x extender, which even when shooting at the 312mm telephoto-end focal length
, delivers superior optical performance to support use with 4K broadcast cameras.
One might now ask--if Digges had had access to optics similar in size and focal length
to those that I used, would he have produced a viable terrestrial telescope?
Rhodri Clark.: How they work:Any camera lens has a focal length
, the distance from the film to the main focal point of the lens.
The simplest way to increase the field of view is to use a low-power eyepiece, but ultimately a scope's field of view is limited by its focal length
and by the diameter of the focuser tube.
Alternatively, lenslets for such an array could be made with a much lower numerical aperture (which automatically reduces their optical aberrations) while still having a focal length
much smaller than would be possible with macroscopic lenses.
However, since there is only one focal length
, there are only three lens parameters, F, [Alpha] and [Beta].