There were a lot of posts on this, which lead me to summarize, speculate
and comment.
It appears that there were actually three different hood versions for
the 21/3.5. If like the other WA hoods, the first would be an all metal
screw-in hood and the second a hood with metal base holding a rubber
main portion. Finally, we know, was a rubber slip-on version.
So why, unlike the others, did a slip on rubber version appear later for
the 21/3.5? Here's the speculation: The first Zuiko WAs were very
unusual, and still largely are, for their very small size and 49mm
filter threads. Certainly that all fits in with the OM gestalt of modest
size and weight and common filter sizes. And it works just fine for the
35, 28 and 24 mm lenses. But it gets a little dodgy with the 21.3.5.
With the rather thin Oly filters, vignetting generally isn't a problem,
but with some other brands, and polarizers in particular, it does become
a problem.
None of the Oly screw-in hoods has threads to hold a filter, presumably
to avoid vignetting, so the only way to use both filter and hood is to
put the hood on the front of the filter. That, however, changes the
spacial relationship between front node and hood in a way that makes
vignetting more likely. About all that can be done with a screw-in hood
is to have sort threads, to make sure it sits back as far as possible,
and have it fall away from the 49 mm threads very fast, with as short a
"tunnel" as possible, and the Oly screw-in hoods generally do this. My
assumption is that this just wasn't enough for the 21/3.5, so another
solution was used, a slip/clamp-on hood. With that design, the location
of the hood is intended not to change with the use of filters. The hood
is supposed to sit back on the front of the lens itself, not clamped to
a filter, so the original, careful coverage design in unaltered by the
use of a filter.
So that works fine with most filters, but not necessarily with
polarizers. I don't have an old Oly 49 mm linear polarizer, but I'll bet
the 21/3.5 hood will fit over it and fit properly on the lens. Back
then, Oly took even the smallest details of system integration very
seriously. Adjusting polarizers within a hood can be difficult on longer
lenses, but the 21.3.5 hood is so wide and flat that it is no problem.
I have two 49mm polarizers, a decades old linear and a newish circular.
Both have a knurled section and a smooth section. Now why the same brand
would knurl the part that screws in on one and the part that you turn to
adjust it on another I don't understand! In any case, on one, the
knurling is too large in diameter for the hood to slip over it. With the
other, the hood slips over fairly easily. this makes a very nice set-up,
with the hood in its proper place and the polarizer easily adjusted. The
one that fits is a Hoya "High-Quality Cir-Polarizing" filter
manufactured in the Philippines that I bought in the last year or two on
eBay. My cheap plastic digital caliper says the one that is too big is
51.6 mm in diameter at the widest part. The one that does fit measures
50.9mm.
Finally, a personal preference comment, to balance all the folks who
dislike slip-on hoods. Slip-ons are my favorites. Now that's partly
because they will work best with a filter or filters, as explained
above. But mostly it's because the let me put the lens cap on with the
hood on! I can't believe others don't also find this a big plus. Many of
my lenses simply always have the hood on, and I like to be able to store
and carry them with a lens cap on too, particularly where wind, dust
and/or water tend to get on the front element. With some longer lenses,
like the 85/2, 100/2.8, 135/4.5, 35-105/3.5-4.5, etc. it's pretty near
impossible to use Oly caps with the hood on, but the wonderful center
pinch Tamron caps work perfectly that way for the 55 mm size and the
less wonderful, but functional, Hama caps work for 49 mm. so the
35-105/3.5-4.5 sitting here on an OM-4 loaded with film is ready to go
with both hood and cap on it.
Moose
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