Zoom range of digital lenses

WillyNelson · 7 Jul 2006 at 19:42

I was just reading up on the Nikon 50D and came across this in the blurb about a lens:

With a practical wide-angle to telephoto zoom range of 18-70mm, this Nikkor lens offers the a 35mm format equivalent of a 27-105mm lens.

Can someone explain that to me please. How does an 18-70mm lens have the equivalent of up to 105mm?

Alex53 · 7 Jul 2006 at 19:47

The sensor in the camera is smaller than a standard 35mm frame. That means you get a cropped view of the image the lens casts. Since the sensor in Nikon DLRs is 1.5x smaller, the field of view you get is the same as that of a lens thats 1.5x longer.

Some people think of it as extra focal length, but if two cameras had the same pixel density and one was full frame and the other a cropped sensor, you could take the same shot with the same lens with the full frame, crop the edges yourself and end up with the same image and same amount of detail.

WillyNelson · 7 Jul 2006 at 19:53

That's what I was wondering. So it doesn't mean you get extra focal length, just a tighter image.

SDK^ · 7 Jul 2006 at 20:06

Nelson said:
That's what I was wondering. So it doesn't mean you get extra focal length, just a tighter image.

Correct

Alex53 · 7 Jul 2006 at 20:10

Yes and no. The cropped sensor cameras can have a higher pixel density, and more pixels for a given area could mean that in my example of cropping an image taken with a full frame camera, you would indeed have more pixels in that given field of view with the cropped camera.

So some people prefere the extra image quality and lower noise of a camera with a bigger sensor and 'larger pixels' and others prefere the 'extra reach' of cropped sensors and also extra frames per second.

And others settle for the in between, a sensor thats only slightly cropped (1.3x of the Canon 1D mk II).