>friend just gave me a Nikon D70 Digital SLR
>camera. I'm wondering if a 28-80 lens is truly like a 28-80 on my
>regular old (Pentax) manual SLR. Also, this friend says that he had the
>option of buying a dedicated Nikon 18-70 lens. Does that REALLY mean
>18mm? - equivalent to what it would be on a regular SLR?
>
>Anyway, since the Nikon D70 is a digital SLR, I'm thinking that the
>lenses are probably equivalent to regular SLR lenses.
The focal length of lenses does not change but the angle of view will change
depending on the "sensor" size. On film we know it is 24x36mm but with digital
it tends to be smaller and so the angle of view of the same lens on a digital
camera is less than it is on a full frame 35mm film camera.
This change in angle of view is often referred to as a focal length
"multiplier" - which in its worst manifestation seems to indicate that the
focal length of a lens varies as one moves the lens from a film camera to a
digital one.
So, a 28-80 lens will function a particular way on your Pentax. When a Nikon or
"off brand" lens of the same focal length is placed on your D70 it will appear
to function as a longer focal length lens but the change is not in the lens but
rather the difference between the size of the film image frame and the CCD
sensor size in your camera. In other words, the same lens at the same focal
length setting will "appear" to have a longer focal length on a digital camera
(unless it is a full-frame - 24x36mm - model) than on a 35mm film camera. Also
in other words, at the same focal length the lens on a digital camera with a
smaller CCD sensor than 35mm film will exhibit a narrower angle of view.
Hmmmmm ... I may have confused myself.
cheers,
andy
