Originally posted by Marc Sabatella I've always understood it to measure the apparent magnification to the eye - relative to without the viewfinder, as is the case with binoculars - measured using a 50mm lens, as Ken mentions.
That's right. And Ken has a point that one cannot use viewfinder magnification figures across different formats to compare apparent size of the image in the viewfinder. But I don't get the fuzz. Viewfinder magnification is clearly defined in terms of a 50mm lens (not in terms of a format normal, which would change with the format), so there is no cheating.
I don't find the magnification figures misleading either, because they refer to a magnification of the viewfinder as such, ergo it has to be relative to the format (size of the sensor). Hence, an apparent size comparison always has to take the format into account. No big revelation of a scandal, AFAIC.
Originally posted by Marc Sabatella This touches on something Robin and I just stumbled upon on in another recent thread: the 35mm format happened to be a kind of "magic" format where a lens that many people perceived as providing a natural field of view (although *nothing* like the field of view of the unaided eye, as is sometimes claimed) also happened to provide something close to 100% magnification using using a basic viewfinder design without additional optics.
But "basic viewfinders" have optics, don't they?
I don't understand the "magic" part. The viewfinder magnification (i.e., the optics between the focusing screen and the eye) is just chosen to be 100% for a 50mm lens. Since viewfinder magnification is defined in terms of a 50mm lens, it pans out to be a 100%.
Originally posted by Marc Sabatella Whereas APS-C provides the same field of view only with a much shorter focal length and an equivalently smaller magnification.
I agree regarding the shorter focal length, but in what sense are you using "magnification" here?
Obviously, it is possible to build a viewfinder that has 100% magnification for APS-C. With such a viewfinder your "magic" would be back, no?
If you are referring to output magnification, then this entirely depends on print size. If you print both an FF and an APS-C image in 6x9 then they will both show the same FOV and magnification provided that the respective format normal focal lengths are used (or any other pair with the correct ratio, i.e., 1.5 for Pentax APS-C).