Originally posted by mtroute Are FOV and Focal length hopelessly connected?
The Field Of View (FOV) is dependant on the focal length (f) of the lens, the dimensions of the sensor (x) and the distance to the object (O). This can be expressed mathematically as:
FOV=x*O / f
and so if the dimension of the sensor is reduced and the focal length and object distance remain the same, then FOV will reduce proportionately. A longer focal length lens at the same object distance will also reduce the FOV
Originally posted by lunelson
Would a picture of the same subject, at the same distance, taken with a 50mm lens at f/4 on the 1.5x camera look exactly the same as a picture taken with a 75mm lens at f/4 on the full frame camera? Or would there be some difference in DoF, distortion, or something else?
Pictures taken at a fixed distance of the same object with a 35mm camera and 75mm lens, and an APS_C camera with a 50mm lens would have roughly the same field of view. The Depth of Field is dependant on many things including how big you intend to view the final image, the lens focal length, object distance, sensor resolution etc and so with both lenses set to the same aperture the DoF may not be identical. Distortion in the image is due to the lens and so could well be different.
Edit: An APS-C sensor has approximately a 1.5X crop factor