Less complicated, I suspect. Try putting one on a 50mm lens, then try
the dedicated hood. You will find that the generic allows light in from
a wider area. I think they make the undefined ones to cover something
like a conventional design 28mm lens. And I doubt if they do any fancy
calculations. Probably just measure the dimensions of 3-4 major brand's
matched hoods, make the angle a bit wider to be sure of avoiding
vignetting and roll 'em out. Some are sold in 3 varieties, WA, Normal
and Tele, which may help. Sort of like a cheap tripod, they are better
than no hood.
You do understand that hoods on all zooms but the 2 mentioned yesterday
are made for the shortest focal length and provide progressivly poorer
protection as the focal length gets longer. It's one of the main
performance differences between the best zooms and fixed focal length
lenses. An older, single coated 200mm lens with a proper hood may
outperform a super quality, latest multi-coating xx-200mm zoom with its
'fitted' hood in some difficult light situations simply because
extraneous light gets into the zoom causing flare and reducing contrast.
Moose
John Cwiklinski wrote:
Moose wrote:
Film plane doesn't work. You need to know where the front node of the
lens is relative to film plane or front of lens or rear of lens
mount, etc. Then it would be simple geometry.
<<
The generic lens hood (i.e 49mm lens hood) then must take an average
of the front node of the lens relative to film plane. Or is this more
complicated? Just curious.
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