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Forum: Pentax K-S1 & K-S2
04-18-2017, 08:16 AM
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The physical focal length of the lens is a property of the lens that doesn't change regardless of what sensor is in the camera. The lens doesn't know how big the sensor or piece of film is. At some level, it doesn't make sense to speak of what the lens sees, only what the sensor sees with a specific lens. Thus, crop-factor doesn't change what the lens sees, it only changes how much of field of view gathered by the lens is captured by the film or sensor.
To answer your last question: an APS-C sensor with a 35 mm lens sees the same field of view as a full frame sensor with a 52.5mm lens. (Yet by some definitions a DA 35 and an FF 35 may "see" the same thing -- what matters is the sensor.)
The entire notion of "equivalent focal length" is a bit wrong, because it's not the lens that is different but the sensor.
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