I am the proud new owner of two Wollensak 159mm Wide Angle lenses for 8x10 :
6"1/4 8x10 Serie IIIa EX.W.A. f12.5 in barrel (serial 313657 - uncoated - no dots)
6"1/4 8x10 Series III f9.5 Wide Angle (serial 249391 - uncoated - no dots) mounted on Alphax shutter
After servicing the shutter of the f9.5, I noticed that the aperture scale on the shutter goes from f3.5 to f22 hereby leading me to think that maybe this lens was simply mounted on a shutter that was just available without due concern for the scale, even though the shutter is fitted with a plate that reduces greatly the maximum aperture that one could get from this shutter.
Since I have a close relative of that lens (the f12.5), I figured I could make myself an appropriate shutter scale for the f9.5 by comparing aperture diameter on both lenses, checking myself along the way with the f stop = focal length/apparent aperture diameter rule. Well, I was surprised to find out that my f12.5 barrel lens with original diaphragm does NOT conform to that rule, whether I measure the diaphragm diameter with or without the elements. Also, if ever the scale on my shutter is really a proper scale, the corresponding apertures would be quite different from the aperture observed on the barrel lens.
My uneducated guess is that the f stop = focal length / aperture diameter rule simply cannot be applied for such Wide Angle lenses. Anyone would care to comment / provide a simple explanation ?
Also, anyone with an Alphax mounted W.A. f9.5 would care to share the extent of the aperture displayed on his shutter and confirm that this f3.5 to f22 scale is indeed the appropriate scale for that lens (even though reading below 9.5 are meaningless) ?
Thanks,
Puzzled Pierre
Bookmarks