Re: [Leica] help: which correction eyepiece ?

[John McLeod <johnmcleod@worldnet.att.net>]

Richard --

Thanks for the clear and thorough explanation of eyepiece corrective lenses.
 It's things like this that make me appreciate the LUG.  Now I understand
why I've always been more comfortable with a total correction of -3.0 to
- -3.75 diopters in my cameras when my glasses are only -2.75.  Was always
puzzled by this and it's tough to get straight answers from Leica, or Nikon,
or Canon Customer Service folks on this kind of thing.

OK, enough of the compliments.  Now that I've told you my eyeglasses
correction (and I will add that I didn't need glasses until age 20), how old
am I, what will my correction requirements be in 5 years, and what is my
wife's first name?  :)    I bet you'll tell me I'll need reading glasses
soon.
- ----------
From: Richard Clompus <rclompus@voicenet.com> 
To: leica-users@mejac.palo-alto.ca.us 
Subject: Re: [Leica] help: which correction eyepiece ?
Date: Tue, 03 Mar 1998 16:47:08 -0800 

Andreas Frijdal wrote:

<snip>
I am wearing glasses with variable focus +1.25 to +3.25.  What is the
appropriate eyepiece correction I should buy.
<snip>

I will try to give you some advice on this subject.  The above prescription
indicates you are probably between 48-52 years old (I'm not psychic) and
are farsighted.  The variable focus lens you mention is probably a
progressive addition lens (PAL) and is considered a bifocal without lines.
If you view through the upper portion of the lens (+1.25 diopter), it
should give you clear distance vision.  As you lift your chin up and view
through the middle or lower area of the lens, you get the bifocal effect
(up to +2.00 diopters in your case).  

Technically, you should use the distance prescription (+1.25 diopter) for
an eyepiece corrective lens for a camera.  Some SLR viewfinders project the
image of the ground glass out to about 1 meter and not optical infinity.
So to focus at this distance, you may need an additional 0.50 to 1.00
diopter strength above your distance prescription.  The lens' total
corrective power can be simply added for the final prescrpition.  So if the
image through the camera is clear with your distance prescription, then go
with the +1.25 diopter lens.  If it is still a bit blurred, you may need
either a +1.50 or a +1.75 diopter lens to clear it.  Most corrective lenses
come in increments of 0.50 diopters.  

For the M Leica, I would recommend your distance correction (+1.25
diopter).  If you can't get this power, you could then go with either +1.00
or even +1.50.  Fortunately many of the professional SLRs today come with a
built-in diopter compensation wheel so you can simply dial in what you need.
 

The M6 Leica has a thin rubber gasket around the eyepiece to prevent you
from scratching your glasses.  You should remember that with a prgressive
bifocal lens, if you view through anywhere except the top of your glasses,
the image will be blurred.  Learnt o keep your chin down when looking
through the camera with your glasses on.

This is sometimes a difficult subject to grasp.  If you need more help,
please feel free to email again.  I hope this cleared things up for you.

Happy shooting,

Richard
- ---------------------------
Richard Clompus, OD
West Chester, PA, USA