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Re: [OM] Infinity focus & focusing screens

Subject: Re: [OM] Infinity focus & focusing screens
From: "C.H.Ling" <chling@xxxxxxxxxxxx>
Date: Mon, 21 May 2001 10:16:44 +0800
I wasn't follow this thread very closely, but I remember you were not
using long tele (sorry if I'm wrong). The 1-8 is suitable for lens of
300mm or above, it is very difficult to get accurate focus with a
shorter lens. Split image can never focus as accurate as matte screen,
at least to me. The 1-8 screen is just somewhat between a clear screen
and a 1-4 (or 2-4) screen. Just like the case of binoculars, you will
force your eye to focus when the focus on the binocular is slightly
out. You should use a 1-4 or 2-4 and try again. 

C.H.Ling

Donald Shedrick wrote:
> 
> I must have not been clear in my explanation.  I took
> 2 shots with each lens - one with the 1-13 screen
> (using the split image on a vertical building edge),
> and one with the 1-8 screen (focused on the matte in
> the center circle) - each focused for best focus on
> the distant buildings as indicated by the respective
> screen.  Varimagni finder was used at the high
> magnification position in all cases.  With all lenses,
> the split image screen resulted in the best focus
> point as seen through the finder being slightly less
> than the infinity symbol, and the matte screen
> resulted in the best focus point as seen through the
> finder being at the infinity symbol.  With all lenses,
> the screen which gave the best focus on the slide was
> the 1-13.  The slide using the 1-8 screen was slightly
> out of focus.
> After thinking some more about this, I think the matte
> screen is more sensitive to the different focus points
> of different eyes.  Have you noticed how someone else
> using binoculars or a telescope will foucs them, and
> when you look through them, they are slightly out of
> focus for you?  However, the split image screen is
> using a technique of lining up of two images, which
> may not be as different for different eyes.  I guess
> we all have to get diopter correction lenses in our
> eyecups so we can obtain accurate focus, and not focus
> the camera to compensate for our eye.
> My conclusion is use a split image screen for most
> accurate focus unless you have corrective lenses in
> your eyecup.  Thoughts?
> 
> --- Gary Reese <pcacala@xxxxxxxxxxxxx> wrote:
> > Hi Donald:
> >
> > Thanks for posting the results of your test.  You
> > didn't mention the
> > results from a re-do of the 1-8 screen.  Still
> > getting best focus at
> > infinity?
> >
> > Can I surmise that you have the same conclusion I
> > do: use an all matte
> > screen for most critical focus?
> >
> > Gary Reese
> > Las Vegas, NV
> >
> >
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