Remember that both diameter and the distance from the front focal node
in the lens to the front of the hood determine the angle covered. Thus,
two fairly close focal lengths whose front nodes differ in their
distance from the hood mounting point the right direction (by chance or
by design) could indeed both use the same hood as the theoretically
correct hood. Whether Oly did this or not, I have no idea, but it's
possible in cases like the 35/2.8 & 50/1.4.1.8s and the 85/2 & 100/2.8.
The problem with rectangular and tulip hoods is alignment. Unless you
design a bayonet mount that only allows correct orientation, as Oly did
with the 35-80/2.8 and other manufacturers have done, people do silly
things - like rotate the hood rather than the camera for portrait
orientation. I know none of you excellent Zuiks would ever do anything
so silly, but I can somehow imagine myself bumping a slip-on or screw in
hood and not realizing that the rectangualr orientation is askew until
after taking the fleeting image that will now be vignetted.
Moose
Jim Brokaw wrote:
I've noticed that Olympus sometimes uses a hood for more than one focal
length... <>
Rectangular hoods seem like they would be closer to ideal than round hoods,
if you imagine the image-forming light rays as a four-sided pyramid with the
tip inside the lens at the nodal point, then a four-sided hood should be
able to give better stray-light protection without vignetting. But for many
Olympus lenses, the hood is round (which has to be a compromise in the first
place) and then also covers the 35mm and 50mm focal lengths, which means it
must be less effective to the 50mm focal length than it could be... or it
would vignette at the 35mm focal length.
While I know in practice the effect is probably minimal, why didn't Olympus
make dedicated hoods for each focal length, and even better make them
rectangular hoods? With a zoom you're still stuck with shading the widest
focal length best, except that Olympus cleverly worked around that for the
35-70/3.6 hood... seems like they could have done more for the rest of the
lens hood range.
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