In R. Lee Hawkins' OM SLR FAQ
<http://brashear.phys.appstate.edu/lhawkins/photo/olympus.faq.html>
there is a note credited to David Lazaroff that the table given in the
eSIF <http://olympus.dementia.org/eSIF/om-sif/findergroup/eyecup2.htm>
for determining the proper Type 2 dipotric correction lens is incorrect.
The FAQ states:
------------------------------------
NOTE: David Lazaroff reports that the above table was less than useful
in his case. After extensive experimentation with Dioptric Correction
Lens 2 lenses, he came to the following conclusions:
I received the nominal 0 (zero) and +1 versions of Olympus Dioptric Lens
2 yesterday afternoon and measured their powers this morning. I also
remeasured the power of the nominal -1 lens lens I'd received earlier.
The powers are exactly as in the "working hypothesis" I described to you
earlier:
nominal actual (diopters) +1 +1.7 diopter 0 +0.7 -1 -0.3
I haven't been able to test other lenses in the Dioptric Correction Lens
2 series, but I think it would be reasonable to extrapolate the table to
include the others. The rule obviously is:
nominal value = actual power - 0.7 diopter
I can't vouch for the other series, Dioptric Correction Lens 1. I'm
returning the +1 and -1 lenses to B&H and keeping the 0. Its actual
power is closest to the +1 diopter power I knew I needed, and it's the
one that actually works for me.
Here's how I'd advise anyone trying to buy Dioptric Correction Lens 2.
First figure out what actual power of correction lens you need by trying
out other lenses at the eyepiece. If you need a positive lens, take your
camera to a drugstore and try looking through the viewfinder using a
selection of reading glasses. If you need a negative lens, you may have
to beg the help of an optometrist who will let you hold a selection of
negative lenses between your eye and the camera eyepiece.
Once you know what actual value you need, subtract 0.7 diopter from that
value and order the Dioptric Correction Lens 2 whose number is closest
to that value. To be sure you'll get what you need, at the same time
order the lenses with the next higher and lower values. Try out all
three lenses when they arrive, pick the one that works best, and return
the other two.
----------------------------------
I'm here to report that I have just finished checking out two Type 1
dioptric correction lenses and have experienced the same thing that
David did with the Type 2's. My distance prescription is approximately
+1 diopter and, according to the both of the eSIF's Type 1 or Type 2
tables, I should require a -1 correction lens. I was already aware of
David's comment regarding the Type 2 correction lenses. When I spotted
some Type 1 correction lenses at KEH recently I was primed for a problem
and so I ordered both a 0 and a -1. Today I received them and can
report that the best fit for me is the 0. This exactly fits David's
final recommendation for Type 2's. You should subtract 0.7 diopter from
your prescription value and order the nearest available correction lens
to that result.
Other comments: I have verified that the diameter of the Type 1's is
19mm and that they are a perfect fit for the aftermarket teardrop shaped
eyecups sold to fit both OM and Pentax M. These are my preferred
eyecups since they provide much better light shielding than the OM type
1 cups which is important for OM-1 metering.
Finally, the Type 1 lenses I got from KEH are in genuine Oly envelopes
but are not engraved with their power. Be careful not to mix them up.
ps: I can finally focus again.
Chuck Norcutt
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