[OM] devils advocate

[jking]

I have been spending some time thinking about sensor size (film or CCD).
it seems to me that there is a counter argument to big is better and I
think it goes somthing like this.

Ok the laws if ohysics and particularly defraction limit resolution as the
size of the hole the appature blades makes gets smaller. So for high
resolution (assuming a perfect lens) to run at less than f8. Now the
larger the sensor you have the higher the focal length you need to cover
the same area as a small sensor for example by 6x4.5 bronica needs a 40mm
lens to cover the olympus om4ti's 24mm lens. Since depth of field/focus
decreases with focal length large sensors require higher appature number
for the same depth of field and become defraction limited. To get the same
depth of field out of my 40mm Bronica lens as my olympus 24mm at f8 I need
f16 which according to Ziesses web site on theretic resolution vs appature
is the difference between Therefore small sensors win because you can get
the same depth of field as a larger sensor AND get less defraction.... at
f8 ziess suggest 200lpmm is possible at f16 its half that.

the table is taken from ziess'es web site

f-no......................resolution
.............................(line pairs per millimeter)
.45.............................35
.32.............................50
.22.............................70
.16...........................100
.11...........................140
...8...........................200
5.6...........................280
...4...........................400
2.8...........................560

Any comments?

James






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