I've acquired an Olympus PEN E-PL1 mounting the kit zoom lens and EV-2 electronic viewfinder. Somehow, setting the lens at 25 mm does not yield the field of view I expect from a 50 mm equivalent focal.
I remember aiming with both eyes open, one through the viewfinder of my Pentax ME Super with SMC Pentax 50/1.7, and seeing the two images as one. With the Olympus, the viewfinder shows smaller objects, so I'm not able superimpose the two images and see them as if I weren't looking through a viewfinder from one eye.
I should note that I'm able to do what I say by setting the zoom lens on the Olympus somewhere between 35 and 42 mm (70-84 equivalent): in that case I see the image with exposure data and other informations superimposed, which is my goal. The focal length at which this happens, which is 70-84 mm, is wrong: human eye has the same field of view of 50 mm on 35 mm film and since micro four third sensors have a crop factor of 2, this should happen at 25 mm.
Where does the problem lie?
The camera (Pentax ME Super) has a viewfinder magnification of 0.95x, so what I see in the viewfinder of the Pentax is slightly zoomed out. This can't justify such a big difference: on the E-PL1 I must set the focal length of the lens to 70mm (equivalent) at least, otherwise things are too small.
I discovered that viewfinder magnification (which should be 1) are given with a 50 mm lens mounted also with the micro 4/3 sensor, so my EV-2 has a magnification of 1.15x/50mm*25mm=0.57x when mounting a 25 mm lens. The 25 mm lens gives me the same FOV of human eye on the micro four thirds format (2x crop factor). The real problem here is the viewfinder and its misleading magnification rating. To get a 1x magnification I have to set the lens focal length to 25mm/0.57x=44mm, which is true because I tried and could perfectly superimpose the images from both eyes (one with viewfinder), but this makes the lens a telephoto. The problem is unsolvable: if I could set the viewfinder to show a 1/0.57x=1.75x version of the image, I would lose coverage. Picture composition would be approximate since I'd be viewing 57% of the final picture, but I'd have a 1x magnification. I suggest to read this nice article: (http://www.luminous-landscape.com/tutorials/understanding-series/viewfinders.shtml)
Answer
The difference is that the crop factor doesn't apply to your eyes.
A 50mm lens on an SLR appears to have the same "focal length" as the human eye, because the lens combined with a typical optical viewfinder magnification results in an overall magnification factor of 1.0 x, hence if you look through the viewfinder with one and whilst keeping the other open, objects appear the same size with both eyes.
A 25mm lens will give a wider absolute view, which when used with a smaller sensor gives the same field of view as a 50mm lens on a 35mm SLR. However this doesn't matter to your eye which just sees the absolute field of view.
The VF-2 electronic viewfinder on your Olympus has a magnification of 1.15x, so the 50mm lens on your ME has effective 47.5mm, whereas the 25mm lens has effective 28.75mm
This is why you have to zoom your lens to 35mm (70mm equivalent) to get close to how your 50mm looks.
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