Originally posted by Jonson PL I’m not sure I understand this difference in calculation magnification, between FF and crop sensor

you do not need to understand the difference.

Here are rough formulas for calculations:

Assuming we have:

X = coverage/100% (E.g. 95%/100% = 0.95 > for Pentax K20D)

Y = magnification (E.g. 0.95x > for Pentax K20D)

Z = sensor size [width x height] (E.g. 23.4 x 15.6 mm > for Pentax K20D)

1) maximum size of viewfinder = MSVf

MSVf(width) = Y * Z(width)

MSVf(height) = Y * Z(height)

2) actual size of viewfinder = ASVf

ASVf(width) = MSVf(width) * X

ASVf(height) = MSVf(height) * X

So fot the FF sensor you have to apply it's size (not Z I have used).

NOTE: but actually these calculations are not true.

Here's why (calculations made for K20D).

MSVf(width) = 0.95 * 23.4 = 22.23

MSVf(height) = 0.95 * 15.6 = 14.82

So the area we have on sensor is 23.4*15.6=365.04 square mm

And the are we get from calculations assuming it 0.95 maginification is 329.4486

And 365.04*0.95=346.788 (which is not equal to calculations we made).

And then after you have to apply second formula which will give even more inaccurate results, but....

END OF NOTE

...you can use then as an example or better understanding of the whole thing.