> I'm not by any means an expert on optics, but here's what I've read any my > understanding (I'm sure many of you already know this): The focal length of > a lens does not change when you put a lens on a digital camera with sensor > smaller than a 35 frame of film. Wrong: that has been the case since the dawn of optics (centruies ago) but the digital "revolution" has changed all that.
Why would it? The physics of the lens haven't changed just because the recording medium is digital.
Now focal length is officially defined by the angle of view of an equivalent 35mm camera (judging by what the experts write in camera
mags)
Really? I didn't know that. That must be "officially" as in "marketing usage".
> A non-full frame digital camera gives a crop, NO!
The lens has a bigger circle of coverage than is being used in a digital camera so how can it not be a crop?
Crop is such a negative word, it implies losing something, definately not an attribute to push in the advertising campaigns.
True, but we're not talking about advertising here.
Modern terminology (a spin-off from the advertising spin doctors) is of "focal length multiplication factor":
As you say, invented by the advertisers.
a real bonus of using a smaller sensor. No more do you need expensive big lenses. The
smaller the sensor the bigger the focal length: "infinity in a single
pixey" ;o)
A real drawback is wide-angle lenses. In fact, this may be a bigger drawback than the bonus because of the complexity of making wide-angle lenses. To get around this I would think that a smaller lens meaning smaller lens mount will have to be made.
> i.e. you could achieve the same with film (resolution and depth of field > aside) by cropping to a smaller part of the frame and scaling that part up. Doh, Heretic!
Why? I'm thinking that it's the advertising people that are the heretics here, redefining something that has been in use for centuries.
Before you know it people will be using masking tape to achieve "focal length multiplication" of thier film cameras ;o)
Actually they would be cropping the image. Just as a non-full frame digital camera does.
-- - Marius
* **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
