Some time ago I made a graph comparing the apparent viewfinder size for a number of SLRs, just to show what the specs really mean. A number of Readers asked if I would expand that comparison, including also the newer models. So here it is.

The apparent viewfinder size, computed in a given dimension, is a product of three values:

• The effective sensor size (in that dimension); more exactly, the size corresponding to the resulting image. (This excludes photosites near the edges.)
• The finder coverage as a fraction of image size in that dimension. (Usually that coverage is the same in both dimensions; the only exception I know of was the Sigma SD10.)
• The finder magnification. It is important that all cameras compared use lenses of the same focal length (50 mm is customary), set to infinity.

The result of the multiplication will be in millimeters, and it does not reflect the finder image size as perceived by a human viewer. What is important, however, is that the former is strictly proportional to the latter, so that results can be directly compared between different cameras. Similarly, the area values in mm² do not make sense as absolute values, but can be meaningfully compared between various models.

Here is a table I compiled from manufacturers' specs published on the Web. The second column ("Model") lists the most recent model with given specs; the last one ("Same as") adds models of exactly the same parameters. While I was trying to avoid any transcription errors, some may have crept in; let me know if you spot anything fishy here, and I will verify the offending data item, correcting it if necessary.

The finder magnification and coverage are rounded by the manufacturers to the nearest 0.01 (approx. 0.5% maximum error), which, when added together, may result in an error of up to 1%. This is why differences below that value are not significant.

The comparison is somewhat obfuscated by the fact that Olympus (and Panasonic) cameras use a 4:3 aspect ratio, not 3:2 like all other SLRs.

• One may argue that most pictures are cropped (for prints or screen display) to formats closer to the former, and therefore the vertical (shorter) dimension of the image frame is more meaningful; thus, for example, the finder in the Olympus E-3 is as large than in the Nikon D300, see the picture below.
• On the other hand, the subjective impact of the finder size seems to depend mostly on its width (longer dimension). People for whom this holds true will perceive the finders in the E-30 and Canon 50D as being of the same size, in spite of the former being significantly taller.

Whatever I may say, you will have to make your own mind on this subject. One possible metrics to be used in comparisons is the apparent finder area, as shown in the table. In these terms, the finder sizes of three models mentioned above are 326 (D300), 297 (E-3), and 268 (50D) square millimeters. (Again, these are not really square millimeters, but the numbers computed this way are directly comparable with each other.)

As things are, the Nikon D300 is unequalled in the finder size department, followed by the D90, Pentax K20D, and Olympus E-3 (what the latter misses in width, it makes up in height). Then we have the Canon 50D, and a tad behind it, Pentax K200D. The Olympus E-520 has the dubious honor of being smallest in terms of the apparent finder area, although the new Sony A350 and Canon 1000D (Rebel XS) are not really better, with only some advantage in width, due to a different aspect ratio, and none in height. (Actually, the finder in the A350 has the smallest, if not by much, height of all current digital SLRs.)

Interestingly, Canon decided to cut the finder size in the 1000D (XS) down by almost 10% from the 450D (XSi), favoring further reduction in body size over viewing comfort. The manufacturers do that not because they are incompetent, but because they believe this will have more market appeal. Unavoidable trade-offs.