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[filmscanners] Re: film and scanning vs digital photography



From: "Berry Ives" <yvesberia@earthlink.net>
>>>>>>>>>>>>>

You're right, Olympus is taking forever to bring out the new model, which
has probably cost them some market base, but I'm waiting for it.  The leaked
info sounds great.  The 14-35mm f2.0 lens is taking even longer, and isn't
expected until next spring, rumor has it.
<<<<<<<<<<<<<

(Sorry to be on your case here: feel free to tell me to take a hike. I find
format comparisons interesting, but end up being a larger-format partizan.)

I realize that an f/2.0 28-70mm equivalent lens sounds pretty cool.

But you are forgetting to take the other aspects of the format difference
into account.

For the same pixel count (to a rough first approximation, 10 is about the
same as 12.7), a 4/3 camera's pixels are 1/4 the area, and thus are two
stops less sensitive.

And DOF scales with the format size, so you "gain" two stops of DOF. (Only
at the wide end, at smaller apertures, diffraction kicks in two stops
sooner, so while f/16 on FF results in sharp images, apertures smaller than
f/8 on 4/3 will show diffraction effects. (One of the early 5D/D2x
comparisons bogusly shot them both at f/16, unfairly making the D2x look
soft.))

So that sexy-sounding f/2.0 lens will be functionally indistinguishable from
an f/4.0 28-70mm lens on FF (with the FF at four times the ISO for identical
noise/dynamic range).

It may be that the f/2.0 bit buys you an AF advantage, but I'm not sure. In
FF vs. APS-C arguments, the point that an extra 1.4x TC is functionally
equivalent to a smaller pixel pitch (test show that TCs do not significantly
degrade the angular resolution of the lens) fails since the 5D's AF isn't an
extra stop better than the APS-C AF, and the 5D can't focus with an f/5.6
lens + 1.4xTC.

Note that to actually be equivalent, the 4/3 lens has to provide _twice_ the
resolution (twice the lp/mm at any given MTF, or an MTF curve shifted up by
a factor of two due to the finer pixel pitch) at f/2.0 than the FF 28-70mm
lens does at f/4.0. (Interestingly, MTF performance does scale up with
decreasing format sizes, so this point may not be a problem; but the need
for twice the resolution at a much wider f stop may be problematic.)

David J. Littleboy
davidjl@gol.com
Tokyo, Japan


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