Martin Trautmann wrote:
> Constant aperture is done by adjustment 'tricks' of the
> efficient aperture
> - the diaphragm blades can be closed for shorter focal lengths.
>
> In fact I don't know why this should be done. 28-70/3.5-4.0 should be
> superior to 28-70/4.0!?
I suppose one point is, that it's from the age of manual and often in manual
mode used cameras (MX,LX,...). With those it's much easier to work, as one
doesn't need to look continuous at the meter. Nowadays with automatic
cameras constant aperture zooms got rare.
The other reason may be at wide open at the short end the vignetting and the
uneveness of the sharpness. If the aperture is closed at bit, these and
other optical faults may be reduce to acceptabel values.
regards
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