Is this right
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mikezs
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This is the case for some DSLR's, but not all.
The Canon xxD series and the xxxD series have APS-C 1.6x sensors (62.5% of full frame)
The Canon 1D series has APS-H 1.3x sensors (77% of full frame, not EF-s compatible)
The Canon 5D and 1Ds series have full frame sensors, no cropping will occur
So basically, different camera's in different ranges have different focal multipliers you can apply to your lenses. Assuming you have a camera in the xxD or xxxD range, your calculations are correct for the actual focal lengths of the lenses!
The Canon xxD series and the xxxD series have APS-C 1.6x sensors (62.5% of full frame)
The Canon 1D series has APS-H 1.3x sensors (77% of full frame, not EF-s compatible)
The Canon 5D and 1Ds series have full frame sensors, no cropping will occur
So basically, different camera's in different ranges have different focal multipliers you can apply to your lenses. Assuming you have a camera in the xxD or xxxD range, your calculations are correct for the actual focal lengths of the lenses!
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Its to do witth the croped sensor, with Canon you X 1.6 as due to the crop missing the edges it gives the impresion of the higher focal lenth, thats how I understand it anyway.
pxl8
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The 1.6x tells you what lens you'd need if you were taking the shot from the same position with a full frame 35mm (film or sensor) so that the subject would be the same size on both. Apart from that the two frames would be different in terms of perspective and depth of field.
Focal length isn't changed by the size of the sensor, only how much of the "image circle" that can be seen.
StewartR
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Time to post my visualisation again, I think. The left hand image simulates the view through a conventional lens that will fit 35mm film cameras and "full frame" digitals like the Canon 5D/1Ds and the Nikon D3/D700. Canon EF lenses and Nikon FX lenses are like this. The right hand image simulates the same view through a "designed for digital" lens with the same focal length. Canon EF-S lenses and Nikon DX lenses are like this.
I would suggest that the only relevance of the "crop factor" is when you're trying to compare lenses on different camera bodies. So for example, I used to have a 28-80mm lens on my old film SLR. Dividing both these numbers by 1.6 tells me that a lens on my 350D (1.6x crop factor) that has the same field of view would be 17-50mm. But if you never shot film, or if you don't aspire to owning a full-frame camera, then you really don't need to worry about this at all.
