On Wed, 28 Feb 2001, Jim Brooks wrote:
> I am afraid that this is "out to lunch". Look for example at the
> 80-320/4.5-5.6 zoom. At 80mm the aperture is 80mm/4.5 = 17.8mm diameter. At
> 320mm the aperture is 320mm/5.6 = 57.1mm diameter (pretty close to the
> filter diameter). AFAIK the variable aperture zoom has the same aperture
> mechanism as a constant aperture zoom.
I don't think you can use the focal length / aperture method to determine
the diameter of the open aperture blades, can you? The aperture blades
can't have an opening of 57mm, because that's larger than the rear of the
lens! If anything, that formula might determine the minimum size that the
front element has to be, but I can't see it measuring aperture
diamter. So, I think I'm going to stick with my theory for now. :)
chris (this could change at any moment, though)
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