On the shooting data for this shot it reads 67.7 mm I have not taken any courses of anykind in photography as I tend to learn from logic.So does this mean the focal length is the distance from what the lens first focuses on to 67mm further back? I was about 4 metres away from these ducks. And no Donald you don't have to look at these LOL

No no no!!! You have to put the Duck WaRnInGs in the header. It's too late after I've already seen them. And look at the weird one with his head on backwards!!!! HOW IS THAT NOT EVIL???!!!!!! Anyway, focal length is the distance between the center (optical center) of the lens to the focal plane (film or sensor). -=>Donald

But if I warned you.. You may never have replied. Thank you. I will read more about this now.

Doug: be warned to refer to focal length allways (if you are using a digital camera, for the sake of comaparability) rescaled to 35mm film format - the conversion factor depends on the camera type (i.c. the sensor size)....

Focal length for digital cameras isn't calculated any different than for film cameras. People just use the wrong terminology. When someone says a 50mm lens on a Canon EOS 10D has a "focal length of 80mm", what they are trying to say is that the 50mm lens on a EOS 10D has the "angle of view of an 80mm lens". The focal length remains 50mm. It's another one of those things that just pokes me the wrong way (like the companies and media calling it a Multiplying Factor and not a Cropping Factor). -=>Donald

How insensitive to get Donald with the Duck...it will drive Him "Quackers"

Attached Link: http://www.sweeting.org/mark/lenses/

This link may help you understand the effect of lens crop. Like Donald says a 50mm lens is a 50 mm lens whatever camera it is on, the difference being that on a 10D etc not the entire lens is used therefore giving the effect that the lens is of a longer focal length than it actually is As I understand it this means that a percentage of the outer lens view is not used (what a waste of quality glass)

pretty ducks