Whoa, whoa, wait a minute here.
1. The 'tulip' shape is exactly equivilent to a rectangular, full-length
hood, but physically smaller and less obtrusive. Do the 3-D geometry on
your CAD program. It doesn't matter whether the light path is
interrupted close to or far away from the lens. Whether that light ray
to the far corner of the image sneaks past a corner of a rectangular
hood 4" away from the glass or through a curved notch 3/8" from the
glass, the effect is the same. I assume tulip hood designs became common
after is became relatively easy to design them with computers.
2. The 'tulip' shape is no more effective at longer focal lengths on a
zoom than any other hood design.
also
3. They are sexy for the same reason that flowers and Julia O'Keefe's
paintings of them are sexy, flowers are sex organs and many are
reminiscent in form to human sexual organs.
om@xxxxxxxxxxxxxxxx wrote:
Actually, hoods don't "HAVE" to be petal shaped for a zoom. But if they
weren't, the lens designers would have to design a hood that was optimized
only for the wide-angle setting of the lens. Any telephoto-designed hood
would vignette at the wide-angle setting. So they opt for a compromise.
Skip
Original Message:
-----------------
From: Tom@xxxxxxxxxxxxx
They have to be petals for zooms.
Every little bit of shade helps, especially with zooms.
Besides, they're sexy.
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