[Leica] Digital "crop factor"

[jonathan at openhealth.org (Jonathan Borden)]

Mark Rabiner wrote:

> I think all you guys have yet to hit the nail on the head on this one.
> "crop factor" is a meaningful term because if you are using a 100mm 
> lens on
> a 35mm cameras system you have lots of bodies to choose from and they 
> all
> are normal 35mm 24x36mm format bodies.
>
> But if you put that lens on a body with a CCD or film even which is 
> APS-c
> sized as most digital is and which is 25.1x16.7mm you have a 1.5 crop 
> factor
> and a smaller needed image circle and a smaller format diagonal.
>

The only reason that 'crop factor' is meaningful, really, is because it 
is in general easier to design a particular lens having a particular 
resolution, etc. when the coverage is less. For example the Schneider 
Super Symmar XL 150/5.6 -- considered an *exceptional* super wide angle 
for the 8x10 format ... aspheric yada yada yada, with lots and lots of 
lpmm **for 8x10** but if you were to slap this on a 35mm it would be a 
downright dud ... super expensive, slow, low resolution etc.

So basically for the APS-c factor you are 'paying for' a 35mm format 
lens but only the APS-c lpmm.

Jonathan