Digital question on lens

C_lawgik · Nov 16, 2004

On a digital SLR such as a d70 you will get an extra amount of zoom correct? How much is it?

santino · Nov 16, 2004

1,5? something like this

Big Mike · Nov 16, 2004

There is a big misconception that you get more "zoom" with a digital SLR (with APS sized sensors).

What you actually get is a cropped image. You will end up with the field of view of a lens with a focal length (1.5 or 1.6) times longer but you don't actually get a longer focal length.

Of course, this really only matters if you were to print the digital file at the same ratio (sensor to print) that you would enlarge and print a 35mm negative.

So you don't get more zoom but you can view/print the digital file at whatever size is acceptable to you.

santino · Nov 16, 2004

yay, I was right, 1,5

Big Mike · Nov 16, 2004

Digital multiplier: Digital multiplier is a term that's come into use with the increased use of digital cameras with a sensor smaller than the frame size of a 35mm camera. Since the angle of view of a lens depends on both the focal length of the lens and the size of the image you can define a "digital multiplier", which is the factor by which a lens's focal length would have to be increased to give the same angle of view was the lens has on a digital sensor. For example, a 100mm focal length lens mounted on a digital camera with a "1.6x" multiplier sensor has the same field of view on that camera as a 160mm lens would have when mounted on a full frame 35mm camera. It's still a 100mm focal length lens, but it acts like a 160mm lens would on a full frame camera.

What we're really most interested in from a photographic viewpoint is the Field of View. If we want a wideangle shot we want a wide field of view (say, 84 degrees horizontal). If we want a "normal" shot we want a "normal" field of view (say, 40 degrees horizontal) and if we want a telephoto shot, we want a narrow field of view (say 6.5 degrees horizontal). For those used to thinking in terms of 35mm cameras these would correspond to lenses with focal lengths of 20mm, 50mm and 300mm respectively. However for 4x5 camera users, they'd think in terms of a wideangle 80mm lens, a 200mm normal lens and a 1200mm telephoto lens. So again, FOV isn't determined by focal length, it's defined by focal length AND format size. That's why when we come to APS-C format digital SLRs (with a sensor approximately 15mm x 22mm) the wideangle lens is now 12.5mm, the normal lens is now 32mm and the telephoto lens is now 188mm. Note that these number are the same as the 35mm numbers divided by a "1.6x digital multiplier" (or in this case, a "1.6x digital divider").

Bob Atkins on photo.net