Quote:
Originally Posted by Peter Mallett
Ah now I understand. I do have a couple of L spec lenses a 70 - 200 zoom and a 50mm f1.8. Both work well with the 7D. I've also got a 100 - 400 Canon Zoom but that is an EF-S.
Ideally I'd like to upgrade to the 1DX 2 with a 300mm lens.
But this is slightly OT.
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The 7D is a 1.6 crop ratio sensor.
The 1DX is, nominally, a "full frame" sensor in the sense that is size is about the same size as the area captured by a 35mm film camera.
So on a full frame body a 100-400 lens captures the same area of subject matter as it would on a 35mm film camera.
A 7D sensor - the common standard reference being an APS-C size - will capture a smaller area of the view for the same focal length. So at 100mm on the lens the area capture on the 7D os the equivalent of what a 160mm lens would capture fitted to a full frame sensor body like the 1DX.
To look at the the other way around, a 300mm lens on a 7D is approximately the same as a 480mm lens of a full frame body. Or a 300mm on a full frame is about the same as a 200mm on a 7D. (Actually about a 187mm but near enough.)
The EF-S mounts fit on a full EF mount but the lenses are intended to be smaller and lighter (and cheaper) and so do not offer full sensor coverage on a larger sensor. Hence the limitation.
My 1D3 has a 1.3 'crop' ratio (APS-H, now discontinued) and so fits between the two common sensor sizes. Quite a good compromise if compromise is required. Obviously Canon feel it is not required.