When I first joined this list, I started out with some questions
about OM eyecups, and how the numbering of the dioptric correction
lenses worked. After acquiring a couple of of eyecups recently from
el bay and another list member, I thought I'd report back what I've
discovered. I hope this might help someone else. . .
I started by trying the eyecup 1--the circular rubber style. I had
heard about the issue that you need to remove the cup to get the film
door open. But I was surprised to discover that with this design, I
could no longer see the corners of the viewfinder on my OM-2n!
I do have unusually deep eye sockets, which may contribute to the
problem. But do other eyecup 1 users notice this? For me, that was a
deal-killer. I never went further in exploring screw-in correction
lenses with that eyecup.
This week I got the "dioptric correction lens 2"--aka the eyecup 2
with a fixed, rectangular correction lens. The full viewfinder is
visible, and the rubber cup is only 3-sided so it does not obstruct
the film door.
Ergonomically it's not perfect, since the top of the rubber surround
tends to collide with my eyebrow ridge, and hold the camera a bit
away from my face. (Perhaps if I mash the OM against my head for a
few months, we will start to fit each other a little better!)
In any case the diopter correction is important enough to me that I
can deal with it. (You OM-3/4 owners in the back, stop snickering)
There has always been some confusion about how Olympus's numbering
system for correction lenses worked--i.e. the "nominal" number was
not the actual, measured, correction of the lens. For example,
there's the mystery of what good a nominal 0 (zero) correction lens
would be?
I have a new working hypothesis, and I'd be interested to hear
whether other people's experience backs this up. I think you're
supposed to choose the nominal number equal to the correction your
eye requires to focus AT INFINITY.
Remember that without any additions, the OM finder appears to be at
4-5 feet. (Someone out there can remind me of the exact numbers.) And
that's why there's a discrepancy.
For my mild nearsightedness, 4-5 feet is just a *little* beyond where
I can focus without glasses. My prescription for focusing at infinity
is about -1.0. And I find Olympus's nominal -1 correction works
perfectly for me. But what I suspect is that the actual correction is
something more like -0.5 diopter.
Meanwhile if you're farsighted, but can focus at infinity without
glasses, you'd choose the 0 (zero) lens. I suspect that is is
actually a weak positive lens (maybe +0.5 diopter?) which makes the
finder's apparent focus distance equal infinity, not 4-5 feet.
Olympus's published descriptions of the correction lenses say that
-1, -2 etc are intended for myopia, while 0, +1, +2 are intended for
hypermetropia (far-sightedness). So that does jibe with the theory
that the nominal zero lens is actually a mild positive one.
Does this make sense to anyone?
-- Ross
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"Do something foolish once, and it's a mistake.
Do it repeatedly and it's a philosophy."
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