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TCav Oct 20, 2010 3:17 PM

Comparison of Eye-level Viewfinders

The "Magnification" and "Field of View" are straight from the spec sheets of the respective cameras. The "Angle of View (H) (50mm lens)" is the horizontal angle of view of a 50mm lens, focused at infinity, and mounted on an APS-C dSLR. The "AoV x FoV x Mag." is the angle of view of the image in the viewfinder. If the Magnification was 1.00x and the Field of View was 100%, then the "AoV x FoV x Mag." would be 27.0, the same as "Angle of View (H) (50mm lens)".

Normal visual acuity is 20/20 which is when the human eye is able to resolve detail as small as 1 arc minute, or 1/60 degree. So "Optical Resoution (20/20)" is the number of arc minutes in "AoV x FoV x Mag.". "Opt. Resolution/Degree" is the "Optical Resoution (20/20)" divided by the angle of view, and represents the level of detail the eye can discern in the image in the viewfinder.

The spec sheet for the A55 gives the electronic viewfinder 1,152,000 available pixels. If the electronic viewfinder has an aspect ratio of 3:2 (which is not very likely), and the image spans the width of the electronic viewfinder (also not very likely), then the horizontal resolution of the image in the electronic viewfinder is 1,314 pixels. Divide that by the angle of view, and the "EVF Resolution/Degree" of 48.69.

Given the unlikely assumptions about the electronic viewfinder in the A55, that would make it better than the optical viewfinder in the A580, but not as good as the one in the A700. If the aspect ratio of the EFV is 4:3, and/or the frame does not span the width of the EFV, then the EFV isn't as good as the OFV in the A580 and much worse than the OFV in the A700.

Any comments?

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