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About viewfinder magnification

Doug Kerr

Well-known member
A camera parameter about which we regularly hear (for cameras with an "eyepiece viewfinder", optical or electronic) is viewfinder magnification. What is that?

Viewfinder magnification is ration of the apparent size of an object (adjudged from its angular size) as viewed though the viewfinder to the apparent size of the object viewed "directly" from the camera location.

But of course we quickly realize that, if we for example consider a zoom lens, the apparent size of an object seen through the viewfinder depends on the focal length we have in play. So how do we deal with that as we attempt to assign a number to "viewfinder magnification"?

Well in full-frame 35 mm single lens reflex cameras (with "through the lens optical viewfinders"), the convention was to report the viewfinder magnification with a "normal" lens aboard, and that generally meant a 50 mm lens.

Now, as we moved into the world of digital SLRs, often descended from film body families, it might seem that it would make sense to report the viewfinder magnification with a lens aboard giving the same field of view as would a 50 mm lens on a full-frame 35 mm format size camera.

But Canon, for example, in their 5/3 format size ("APS-C") digital SLR's reports the viewfinder magnification with a 50 mm lens aboard.

So the user viewfinder experience with two cameras, one with an 8/3 ("full-frame 35-mm) sensor and one with a 5/3 ("APS-C") sensor, both equipped with a lens giving the same field of view (e.g., a 50 mm lens on the 5/3 camera and an 80 mm lens on the 8/3 camera). where both viewfinder had the same reported viewfinder magnification, would be quite different.

And in fact, the stated viewfinder magnification for the smaller-sensor camera would be "misleadingly large".

Now today, when we often deal with sensor sizes significantly smaller than 5/3 (perhaps 3/3 - "one inch" - or 4/3 - "Four Thirds"), and see a viewfinder (perhaps an EVF) rated as having a viewfinder magnification of "0.85", what does that mean. That is, it would exhibit that viewfinder magnification with what lens focal length in play?

My guess is that, for manufacturers other than Canon, it would be with a focal length in play having a full-frame 35-mm equivalent focal length of 50 mm. (Such appears to be the case for my Panasonic FZ1000.) That is a very sensible approach, considering the history of that parameter. And the non-Canon manufacturers of such machines have not been schooled in "the Canon Way".

But if we now consider a camera such as the Canon EOS M5, how do we interpret its stated viewfinder magnification (which number I have not yet seen)? Well, sadly, I suspect it would be with a lens focal length of having a full-frame 35-mm equivalent focal length of 80 mm (that is, a focal length of 50 mm). "It's the Canon way."

But I don't yet know.

Best regards,