I interpreted Scott's question to be a reference to the completely clear
screens - 1-9, 1-11, 1-12.
1-9 is the odd one, designed for use with endoscopes. It is UNUSABLE with a
photographic lens to my understanding.
1-11 and 1-12 are completely clear screens for macro and micro use, to get
as much visible image as possible in the dim conditions which are usual in
such applications. The result is that the screen provides an "aerial image"
which can appear to be in focus at all times. To focus using those screens,
you first have to "tune" the camera focusing system to your eyesight. On
models with built-in dioptric adjustment, do this by taking off the lens,
then adjusting the dioptric until you can see clearly the cross hairs on the
screen. Then with the lens fitted, focus by keeping the cross hairs in
focus, and adjusting the camera/subject position until the image is also in
focus.
--
Piers
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx] On Behalf
Of Simon Worby
Sent: 03 May 2005 21:27
To: olympus@xxxxxxxxxx
Subject: [OM] Re: Simple question about 'clear' screens
ScottGee1 asked:
> From the archives my understanding is that one cannot focus with the
clear
> area, but rather the focusing aid is used to focus - correct?
The focussing aid (split prism / microprism) is not *needed* to focus, but
it can be helpful. However, without anything (ground glass or focussing
aid), focussing is impossible.
What you are doing when you focus, is to get the image on the focussing
screen sharp and in focus. If it's clear glass you can't see the image on
the focussing screen as there isn't one; hence it needs to be at least part
ground glass with or without a focussing aid.
The focussing screen is at the same distance from the subject as the film
will be when it's exposed to the light. Hence you are making sure the image,
when it's projected onto the film, will be in focus.
To the eye, due to the various lenses, the focussing screen appears to the
eye to be about 6 foot away, though in reality it is but an inch or so away.
(It's not possible for normal humans to focus down to an inch!)
> <snip> Also, how much brighter/clearer are the clear screens than a
comparable
> 1 series matte screen? 2 series?
I think a stop or so. But, IMHO, they are almost impossible to use except
for specific purposes. Unless you have a specific purpose in mind, I would
recommend a ground glass screen of some description, with a focussing aid.
Some photographers like not to have the focussing aid (as per 1-4 or 2-4)
but personally I think they make life hard work.
Regards,
Simon
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