In a message dated 5/21/01 11:54:04 AM Eastern Daylight Time,
watershed@xxxxxxxxxxxxxxx writes:
> Now I'm thinking that maybe the
> distance to the focusing screen is more critical. Should I remove my
> glasses to focus? And similarly, should one focus using the bifocal or
> the long vision part of the lens?
Again, this depends on your particular set of peepers. As we age, the
interocular lens hardens and loses elasticity, which is why we lose the
ability to "accomodate" (focus) and need bifocals. (In order to focus, we
"squeeze" the flexible lens and therefore focus on whatever we look upon.
When this hardens, no amount of squinting will flex that lens anymore!) For
most, this lack of 'accomodation' is mainly in the near, or reading zone, but
for around 20%, they also need magnification in the mid-zones as well (hence,
trifocals...a near, mid-range, and distance.) Progressive bifocals are
perfect for this as they give you ALL focal lengths, an you merely move your
head up or down to find YOUR zone.
Carl Shipman stated in his 'How to Select and Use Olympus SLR Cameras", Rev.
ed., 1989, p.66.:
"The focusing screen in SLR cameras appears to be at about arm's
length.Therefore, the diopter number you need is the one that corrects your
vision for objects at arm's length".
Arm's length is NOT your bifocal strength (average 16" from your nose) but
rather, your mid-range....so your abillity to focus on the focusing screen
will depend greatly on your particular eye's aging process, and how quickly
your lens will harden as you age. This is the same for those that need
computer glasses...the mid-zone is difficult for them to focus on, as their
hardening is much further along.
If you cannot focus well with your current plano (distance) lenses, nor with
your readers, then go get glasses made for your mid-zone, specifying to your
optician the approximate distance you need. You wil also be able to use them
for gardening, playing the piano, and typing letters to your OM buddies.
Later, when you get the eventual progressives, you can tilt your head up
until you find the mid-zone for focusing.
Susan Steele
Virginia USA
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|