Hi Ken,
You have just given me the technical explanation to support my own
observations. I have a Leica Elmarit-R 28mm lens that I sometimes use as a
"standard" (56mm equiv) lens on the E-1 and E-510. Focusing can be very
difficult. I usually end up setting the hyperfocal distance and shooting it
fixed-focus. 50 and 55mm lenses work ok, and by 60mm, all is well.
Thanks for the explanation.
Jim Nichols
Tullahoma, TN USA
----- Original Message -----
From: "Ken Norton" <ken@xxxxxxxxxxx>
To: "Olympus Camera Discussion" <olympus@xxxxxxxxxxxxxxxxx>
Sent: Wednesday, September 21, 2011 9:39 AM
Subject: Re: [OM] Any limitations on Zuikos with Canyon digital?
> >
>> Of course, if you usually expose to the right as I do, chimp the
>> histogram and let the meter be damned it doesn't matter at all.
>>
>
> And if a person uses a "real meter", or shoots "box speeds", it really
> makes
> things even less an issue.
>
> The biggest issue that I've encountered has to do with the Olympus focus
> screen itself. These ultra-matte or whatever they are called screens are
> NOT
> ground-glass type of screens. The matte area is actually what they call
> deformed microprisms. Inotherwords, you aren't looking at a random
> scattering surface like a traditional ground-glass screen, but instead
> it's
> a surface entirely made up of microprisms (pyramids).
>
> As we remember from the film days, the focusing aids in an SLR comprised
> of
> a split image (two opposing slopes) and a microprism collar. If you used a
> too dim focus screen with these screens the focusing aids would black out.
> The solution to this was to reduce the angle of the prisms. This had the
> unfortunate side-effect of slowing down the focus aids. The aids wouldn't
> black out, but they also reacted oddly with wide-angle lenses with
> rear-nodal points close to the film-plane..
>
> Then Olympus came out with the 2-series focus screens where they replaced
> the entire ground-glass portion of the screen with a very fine microprism
> mesh. To keep from blacking out with dim lenses, though, they kept the
> angles pretty shallow. Well, the problem there is that the angles which
> the
> light exits a wide-angle lens (especially bright ones with a large
> diameter
> exit pupil) is such that you really don't get much useful angular spread
> going on with the microprisms. A 35mm lens, for example, is very difficult
> to focus on a 2-series screen because the image barely mushes into and out
> of focus.
>
> So, we progress to the digital age. Olympus has continued to use the
> microprism mesh from the 2-series screens but adapted the angles of the
> pyamids to be better for telecentric lenses. This makes trying to manually
> focus wide-angle lenses that don't have a a rear-nodal point far forward
> to
> be difficult.
>
> AG
> --
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