Quote:
Originally Posted by thefonz78
If i got a 70 - 300mm its built to work on both FF and APS-C so the 70mm would have the field of view equiv of 105mm on a aps-c lens. The 17-50mm tamron is built for the aps-c crop and don't apply to the same field of view equation. So I would be missing equiv on 50/55mm to 105mm.
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Wrong. Focal length is focal length. 70-300 is 70-300, 17-50 is 17-50. You're missing the 20mm between 50 and 70. Ignore FOV calculations, they're obviously confusing you. Or apply them to all lenses, but I doubt if you think in terms of 'on 35mm I'd use a 75mm lens here so I need 50mm on DX', which makes the crop factor calculation superfluous.
Chris