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I have a NEX-6 with a number of legacy lenses and the two NEX "kit" lenses. If I fit the 16-50 kit lens, setting it to 50mm, and view the image through the viewfinder, noting the width of the image, and then fit a Minolta 50mm lens on an MD-NEX adapter I note that the fov appears the same and the width of the image is the same as on the kit lens. Why is this? The other legacy lenses seem to behave in the same way.

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Why is this? And why not? 50mm is 50mm and the adapter does not change anything (unless it is one of the very special adapters containing additional optics, like Metabones Speedbooster)

  • But as the lenses focal plane is always the same distance from the lens and if the sensor is in this position surely as the sensor is smaller than the 35mm film area, only a part of this image will be "cut" by the sensor thus giving the effect of the lens having a longer focal length on the NEX camera? – Brian O'Gorman Nov 30 '14 at 16:59
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    @BrianO'Gorman Yes, that's true, but it also applies to the kit lens in exactly the same way. – mattdm Nov 30 '14 at 17:22
  • But if the sensors are different in size (assuming the Minolta was designed for 35mm film) surely the different sensor areas would create the effect of the Minolta when fitted to the NEX having a smaller field of view and thus appearing like a longer lens? – Brian O'Gorman Nov 30 '14 at 17:57
  • @BrianO'Gorman - the 16-50mm kit lens is designed to give the same field-of-view coverage on the crop sensor as a 24-75mm lens would on a 35mm/full-frame camera. The "crop factor" or "focal length multiplier" is there no matter what size the designed image circle (sensor size) happens to be. – user34820 Nov 30 '14 at 18:07
  • Yes, it is quite complicated. the 50mm Minolta has the same size fov as the 16-50 when set to 50, presumably as this is equivalent to a 75mm fov, about the same as the fov of the Minolta. The really puzzling thing to me (and I'm easily puzzled!) is the fact that when using a legacy lens you can just go by the focal length of it and it this case it's advantage over the 16-50 at 50 is image quality, color, etc. – Brian O'Gorman Nov 30 '14 at 18:29

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