Re: 580EX II Zoom Range
Putting an extender on a lens does alter it's focal length, you are changing changing the physic of the lens ( glass and distance)
By using a different sensor you do not change the distance or the glass, all you are doing is using a smaller sensor that gets blown up to a larger size...cropping the image.
A 1.4x entender changes the physical properties of the lens, while changing the cropping factor ( sensor size) does not change anything about how the lens moves light.
Glenn
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