on 10/11/04 1:30 PM, Chris Barker at ftog@xxxxxxxxxxxxxxxx wrote:
> the UK site
> gives what looks like a different result for the 50mm. I don't really
> understand mag factors, to be honest, but the apparent discrepancies
> between regional websites is not very reassuring. It's a great pity
> that there is so little consistency in design of the specification
> table or the units used in them.
Easy way to understand magnification factors is in relation to the sensor
(film negative/slide) size.
For instance, a .25x magnification factor, given that's equivalent to 1/4x
take the reciprocal getting 4x, then multiply the dimensions of the sensor
size (film negative size...) by this factor, that's the subject area taken
in by the camera/lens at that magnification.
An example from above .25x magnification, using my OM-4T with any lens (lens
doesn't matter, just magnification factor) means 4x multiple of the image
size *on-the-film* which is 1" x 1.5" size. Multiply either dimension by the
multiplier, that's the dimension of one side of the area on the subject...
so you're looking at a 4" by 6" (always proportional to the sensor/film
area).
By reversing the calculation from the published data you should come up with
the sensor size... Olympus says .13x magnification, take the reciprocal
works out to about 8x (roughly without a calculator) and the subject area
size is 5" x 3.75". Working backwards I divide 5" by 8 factor, getting .63".
Using the proportions of the sensor which I know to be 4:3 (from 4/3 System)
I then deduce that if the long sensor dimension is .63" the short dimension
must be about .47"... convert to millimeters I get 16mm x 11.94mm -- how
close am I?
OK, I admit I used a calculator at the last part of that...
--
Jim Brokaw
OM-'s of all sorts, and no OM-oney...
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