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Old October 22nd, 2018, 06:06 PM
Doug Kerr Doug Kerr is offline
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Default About viewfinder "magnfication"

We often see. among the other properties of cameras, the parameter "viewfinder magnification. I thought it might be worthwhile to review just what that means.

Under the most-commonly used definition, the magnification of a camera viewfinder is the ratio of the apparent linear size of some scene element (as concluded by the eye from its angular extent) as seen through the viewfinder to that apparent size as seem "looking over the camera" at the scene itself.

But of course in an SLR or the typical EVF era, that ratio depends on the focal length of the lens on board.

In the realm of full-frame 35-mm film cameras, the ration was usually defined assuming the use of a 50 mm lens.

So then, for example, when we move to "APS-C" format digital SLR cameras, would that be a lens with that same field of view (that is, a lens we would describe as having a full-frame 35-mm equivalent focal length of 50 mm)? Well, in the case of Messrs. Canon, no. It meant with a lens on board whose focal length was 50 mm.

So are those two descriptions of the behavior of the respective viewfinders "comparable"? Well, as we learn when we study the engineering disciple of "similitude" (the science of the behavior of "scale models" of systems), there is never any clear way to compare things of different sizes.

Still, I would have thought that to "normalize" this metric of viewfinder magnification, "they" would have proposed the use of a lens giving a consistent field of view (perhaps the field of view given by a 50 mm lens on full-frame 35-mm format camera).

Now, how is this seemingly done with regard to "modern" cameras with formats greatly different from the full-frame 35-mm format? Well, a very agricultural inspection suggest that the view through the EVF of my Panasonic FZ1000 is about the same in (angular) size ( 1 ×") when the lens focal length is set to 80 mm full-frame 35-mm equivalent.

The magnification of the EVF is said to be 0.7 ×. That would obtain for a lens focal length of about 56 mm full-frame 35-mm equivalent.

At a focal length of 50 mm full-frame 35-mm equivalent, the magnification would be about 0.63 ×.

So this all seems to be "about in the right ballpark". Sort of.

Best regards,

Doug
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Old October 22nd, 2018, 07:13 PM
Doug Kerr Doug Kerr is offline
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Default

On the other hand, for a camera with a non-interchangeable fixed focal length lens, it would probably make the most sense to reckon the "magnification" of the viewfinder with that lens in place. Then a value of 1.0× would mean that the apparent size of scene objects as seen through the finder would be the same as seen "looking over the camera", with the only lens it will ever have in place. That would be easy to comprehend.

Could we meaningfully compare that value with the value stated for the viewfinders on cameras that have a zoom lens, or that take interchangeable lenses? Not really. Why might we want to?

Best regards,

Doug
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