Quote:
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Originally Posted by MindBuster
How do you calculate that 
300x1.4 = 420mm, how do you get it to be 672 ?
What is EFL ?
Ya, havent had a DSLR nor SLR before, so i'm reading alot on the subject 
672mm would be cool  |
Digital cameras that are not "full frame" (that is, who's sensor is smaller than a piece of 35mm film) have a "conversion factor" (sometimes goes by different names). The basic principle is that if a lens has a focal length of 500mm on a 35mm camera, if you fit that lens to a camera with a sensor 1.6x smaller than a 35mm piece of film you get an increased level of magnification. As such, you get an extra amount of zoom simply because the sensor is smaller than a full sized piece of film. That "focal length for free" figure is referred to as the
Equivalent
Focal
Length (EFL).
So, with a 350D and 20D both having a 1.6x crop, you multiply the physical length of the lens by 1.6x to achieve the actual focal length you'll see.
That is how you get "compact mega-zoom" cameras. My Canon S2 IS has an actual focal length of 72mm, but because of the size of the sensor it's EFL is 432mm.
The conversion factor has it's plus sides for wildlife and telephoto shooting in general, but you do lose some of the wide end because of it. Because of the size of the sensor, my 17mm wide angle is infact 27mm EFL at the widest setting.
I hope that made some kind of sense
