Millimeters vs. Magnification factor

[durtralp]

Hi Folks,
New to still cameras and don't yet have a "feel" for the magnification factor (x1, x2, x3, etc.) of different millimeter lenses.

Most video cameras are rated by zoom factor.
How does one calculate the magnification factor for the Nikon d90 with a 70-300 mm lens?

I'm guessing it might be something like: lens mm / sensor mm, or something like that.

Thanks,

Ralph, slowly getting a clue

[OldClicker]

Thje 'x' designation is simply how many times larger the long end is than the short end. For the 70-300, it is 300/70= 4.3x. As you can see, the 'x' tells you nothing about the focal actual length. - TF

[Franglais]

"Magnification factor" doesn't mean anything in terms of the view you get. We talk about:

"Normal" view = aboit the same as your perception using your eyes
"Telephoto" view = like looking through binoculars or a telescope
"Wideangle" view = wider than your normal view, often perceived as distorted

For a given sensor size, the focal length needed to give a "normal" view is about the same as the diagonal of the sensor:

- for a 24x36mm sensor this is about 43mm
- for the APS-C sensor that most of us use this is about 29mm

The longer the focal length, the more telephoto the lens. The classic 50mm normal lens for 24x36 is actually a little bit more telephoto than the ideal.