I had an amazing revelation today that may cause some more use of the
OM's. For the last couple of years, and the last year in particular,
I've had trouble getting well focused shots.
I attributed it mostly to my tendencey to do portraits of the grand kids
up close and wide open. This is a formula for frequent failure even if
you see well since the little ones are always rapidly moving targets.
When I first started noticing other focusing problems I did what I was
supposed to do. I removed the lens and checked to see that those nice
grid lines that JH scribed in my 2-13 screens look nice and sharp. I
don't have an OM-3 or 4 with built-in diopter adjustment but, with no
optical aid they did look sharp. I could also see the dust specs on the
screen and they looked pretty sharp too... or so I thought!
Today, while playing around with some close-up lenses, I decided to
check the viewfinder while looking through the +1 diopter lens. I
nearly fell over. The sharp lines and dust specs suddenly became so
sharp they could cut me.
I immediately ran off to the eSIF data on dipotric correction lenses
<http://olympus.dementia.org/eSIF/om-sif/findergroup/eyecup1.htm> and
can now see that that table has always led me astray. According to the
"application" notes on the right of the table someone who wears
glasses of +2 to +4 diopters (me) needs a viewfinder correction lens of
equivalent strength. I wear a +2 prescription when I'm using the
computer or reading in bright light. I also have a +3 prescription for
reading fine print and in dim light. As I read the application table my
own glasses should be suitable. But they never were and only made
viewing worse.
Now that I have stumbled onto the +1 lens as the solution it is apparent
that the correction listed in the Oly table is for the screen at its
apparent distance of 1 meter. This obscure fact about the apparent
distance to the screen is something I've carried in my head for years
and is buried somewhere in the archives I'm sure. It should have been
obvious to me that if my +2 glasses were working OK on the computer at
about 18" then I should need something less powerful to view something
one meter away. To verify that I tried the +1 lens without the camera
and find that it does make things sharp that are roughly 1 meter away.
Amazing when the numbers work, huh?
Now that I know I need a +1 diopter correction; how do I get it?
According to the Oly table I need an Oly lens marked "-1" which is
actually a +1 lens.
Does anyone know the diameter of the eyecup 1 lenses? I much prefer the
cheap tear drop shaped third party eyecups which have provision for a
19mm or 3/4" diameter correction lens. Is this perhaps a standard size?
Does anyone know where to get suitable correction lenses without
custom cutting them out of a cheap pair of reading glasses? Anybody got
any to sell? Should I break down and get an OM-4Ti? :-)
Chuck Norcutt
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