On Mon, 5 Feb 2001 11:37:34 -0500, dosk wrote:
>> Note however that in the two examples above, 2.8->2.0 is a full f-stop
>difference
>> (+1 EV) while 2.8->3.5 is only half a stop (- 1/2 EV) ...
>
>I don't understand this part. Can you elaborate further?
>
Sure!
The term "stop" indicates doubling or halving the exposure.
For the shutter this is why the major speeds roughly double in value as in:
2 4 8 15 30 60 125 250 500
For the aperture, we need the same effect, however the aperture is measured
differently.
The aperture (f) value equals the effective opening divided by the focal length.
So a 50mm f2.0 lens would roughly have a 25mm diameter opening.
The amount of light does not relate in a linear way to the opening diameter but
rather to the surface. The relation between the two is square-root, so for doubling
or halving the the surface (and amount of light), we only need to multiply or
divide the f-value with the square-root of 2 wich is about 1.4
So to make this rather long story short, a range for full f-stops would be:
1 1.4 2 2.8 4 5.6 8 11 16
Now your 3.5 is in between 2.8 and 4, and is about half a stop 'slower' than 2.8
Other 'well known' half-stop values are 1.2, 1.7, 2.5 and 4.5 although some of
these are not exactly 'in the middle'.
Half a stop would be the square-root of the square-root of 2, wich is a 1.19 factor.
>
>> And since your MZ-M is a manual camera, it only affects the readout of the
>meter,
>> changing the compensation-dial on a manual camera without changing
>aperture (f-stop) or
>> shutter (time) doesn't change the exposure at all ...
>
>No, the ZX-M has full auto exposure program plus aperture and shutter
>priority settings, and also motor wind and advance. Only the focusing is
>manual. (Best of this type around, which is why I bought it...)
Yes you are right of course, I guess I only related "manual" to any ZX-M feature :-)
Regards, JvW
---------------------------------------------------------
Jan van Wijk; www.fsys.demon.nl
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