It is not difficulty but focus accuracy which is concerned.
Both split image and microprism turn the rays round in a certain angle, which
depends of the
wedge-angle of the focusing screen ( This angle is minor at the 1-2 screen).
If the angel is too large for the aperture-angle of the lens, the rays can`t
go trough the
apperture, and you can only see the black border of the lens mounting. This is
what happens
when the split image darkens. It also darkens when you`re not locking straight
centered
throught the viewfinder. Fast lenses offer more capability to compensate
angular viewfinder insight.
I tested with 2-13 screen and F/2-lens at which insight angle the splitimage is
darkening:
F/8(d.o.f. preview): split image is always dark.
F/5.6 : split image darkens except very accurate insight
F/4 : small inaccurancy possible.
F/2.8 : just darkens when insight angel is at its maximum
F/2 : viewfinder image isn`t recongizeable before splitimage darkens.
But focus accuracy increases with the wedge-angle, focal length and viewfinder
magnification.
This is why the minor angle isn`t recomended with wide angle-lenses.
hope this helps a bit,
Frieder Faig
On Wed, Oct 18, 2000 at 02:25:45PM +0200, rdk@xxxxxxxxx wrote:
>
>
>
> I use a 1-2 screen in my OM-2n for just this reason. Olympus say that a 1-1
> (or
> 1-13)
> screen goes dark at/after f5.6; a 1-2 screen is first dark after f8. Ithink
> that the reason is
> a coarser microprism. It is also very quick to focus for telephoto or zoom
> lenses.
> The down side is that it is theoretically not good for wide-angle leses (under
> 35mm).
> But I have no difficulty...
>
> Regards, Roger Key
>
>
>
>
> >With any split-image screen or microprism I just find that eye position
> >becomes more critical with slower lenses or stopping down. Find j-u-s-t the
> >right alignment and both halves will be visible with slow lenses or in dim
> >light. Harder for folks who must wear eyeglasses when shooting. Must be a
> >parallax thing.
> >-----------
> >Lex Jenkins
>
>
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