[rollei_list] Re: SL66 & focussing screens
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: "New Rollei List" <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 27 Oct 2014 11:29:30 -0700
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From: "" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "ejdong@xxxxxxxxx" for DMARC)
DMARC)" <dmarc-noreply@xxxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Sunday, October 26, 2014 7:36 PM
Subject: [rollei_list] Re: SL66 & focussing screens
Hi Richard,
Thank You for the in-depth explanation. I use the original
Rolleiflex plastic screens in all of my Rolleiflexes. I
had just (2) Maxwell screen which I dislike for the lack
of "Snap-to Contrast" just the older version plastic
Rolleiflex screen.
With the exception of the Hi D screen in my 2.8E3, all
focusing screens I use in my Rolleiflex are later plastic
screen with either grid line with split image finder or
the large Spot magnifier.
Evan
The Rolleigrid works surprisingly well. There was
another brand called the Hartley Field Lens sold around the
1950s, I've
not seen any in the used market. Hartley made screens for
many different cameras. Kodak also made Fresnel lenses for
several cameras under the name Ektalite Field Lens. I don't
think they made one specifically for the Rollei but they did
make the field lenses found in late Speed and Crown Graphic
backs.
Some of these finder screens have prism type
rangefinders in the center. These can work pretty well but
are affected by the focal length of the lens so must be
matched to at least the range of focal lengths and also do
not work when the lens is stopped down since the effective
base line of the rangefinder is the angle of the cone of
light from the lens. The bigger the lens the better it
works. This is the same principle as the old trick of making
an aerial image focuser by making a clear spot on the
ground glass of a view camera and marking it with something
at the center. When you look at the image through a
magnifier and move the glass around the image will stay
fixed when its exactly in focus. The two opposing prisms so
much the same thing. One can also use an array of small
prisms at various angles. When in focus the image will seem
to pop together, at least in principle. The clear spot on
the Rolleigrid along with the magnifier in the camera seem
to work as well as anything for getting the focus sharp.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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