[greenwing]

Originally Posted by LaPistola

If a 50mm lens isn't 80mm on a 1.6 cropped sensor camera then what is it??

I never said this is focal length but how it will help the OP which was one of his questions and if the OP wishes to know how it helps them they more than likely need to know about the crop factor.

A 50mm lens is a 50mm lens. End of subject. On crop-sensor cameras, we can use the crop factor to calculate a '35mm equivalent' focal length at which a full-frame camera would have the same field of view, but that's really not much use unless you're familiar with what focal lengths look like on 35mm formats, or want to compare different formats - compact, cropped, Nikon 1, medium format could all be compared this way if you want. The vast majority of digiatl SLR users have never used a 35mm camera and don't need to compare their camera to anything else, so the 35mm equivalent is not a lot of use to them. It's like telling someone who's never experienced gravity that they'll be able to jump 6 times as high on the moon than on the earth.

Note that it's a 35mm equivalent, not an 'effective' or 'true' focal length.

Originally Posted by LaPistola

http://www.great-landscape-photograp...al-length.html
http://www.digital-photo-secrets.com...ean-on-a-lens/

Now normally I would bow to others superior knowledge but in this case I don't think im to far off the mark at all and the two above links support what I said and explain the other.



Personally I think explaining what the focal length is instead of how it helps you is confusing. Focal length the measurement between a lens and the image sensor but this isn't always true on all lens there for confusing.

Digital photo secrets is confused. To try to explain focal length by using the close focus distance of a lens defies any form of logic. Very few lenses can focus at a point their own FL in front of them.

No, focal length isn't always the distance between the lens (when focused at infinity) and the sensor. It's always the distance between an imaginary plane and the sensor, I think the plane might be called the Nodal Point, but could be wrong and don't have time to check. In the case of extreme wideangles it's well behind any point of the lens, or it would interfere with the mirror. In the case of long telephotos it's well beyond the front of the lens, otherwise the lens would be unmanageably long. Don't ask me how lens designers acheive these tricks.

Chris