Susan
One warning I will mention about shifting your head back to see a computer
screen with trifocals is that we often look at the screen for long periods
of time. I ended up having to have my neck in traction 3 times a week
because I had compressed some nerves. This caused numbing in my arm and
hand. I now am very careful about tilting my head back searching for the
sweet spot. Instead I try to make sure that I am sitting higher in the
chair and looking more down at screen. This works for me and I have not had
anymore trouble with my neck.
Bob Winters
> From: DaEyeGuy@xxxxxxx
> Reply-To: olympus@xxxxxxxxxxxxxxx
> Date: Mon, 21 May 2001 18:29:13 EDT
> To: olympus@xxxxxxxxxxxxxxx
> Subject: [OM] Optics 102: Aging, Apparent Focusing Distance reference, et. al.
>
> 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
>
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