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INSTALLATION
IS SIMPLE
In camera models with
interchangeable screens installation of the
Beattie Intenscreen™ is as simple as removing the present
viewing screen and replacing it with the
Beattie Intenscreen™. For
some models of camera Beattie Intenscreen™ comes in component
form, in which case installation instructions are
included with the screen. The Pentax 6 x 7 and the
Hasselblad 500C are the only cameras that require a
technician to install.
Brightness
Gains & In-Camera Light Metering
Depending on the camera,
optics and accessories gains range from 1½ f-stops to 4
f-stops. Small format camera gain approximately 1½
f-stops; Medium format cameras 2 - 3 f-stops; and 6 x 7,
6 x 9 , 10cm x 12.5cm (4" x 5") and Panoramic
Cameras 3 - 4 f-stops. Metering systems that read off the
screen (see your user's manual) are affected by the
Beattie Intenscreen™. The following methods can be used to
compensate:
Changing the ASA film
speed - Using your existing screen, set the camera lens
at infinity and looking at an even light, such as a grey
card or blue sky, note the meter reading. Install the
Beattie Intenscreen™ and turn the ASA index dial until the
meter needle returns to the old screen reading. Record
this offset and tape to the back of your camera.
Changing the Exposure
Value (EV) 1 EV = 1 f-stop - In modern cameras there is a
button that can manually change the amount of exposure.
Using your existing screen set the camera at infinity and
looking at an even light, such as a grey card or blue
sky, note the exposure reading. Install the
Beattie Intenscreen™ and push the exposure button until the
exposure needle returns to the old screen reading. Record
this offset and tape to the back of your camera. An
essential part of the design of the Beattie Intenscreen™
Plus bright focusing screen is that a very small
proportion of the light is used through scattering to
form the image and provide focus contrast. The remainder
is transmitted through the screen and collected in a
narrow cone by the special fresnel lenses used. The meter
sensor cannot be in your line of sight and so is slightly
off axis. This means that it may be in the "boundary
layer" at the edge of the light cone and will
therefore not record a significant change even though
your eye may see major brightness changes.
Looking
into the Future
Special screens have
been made for medical, scientific and industrial purposes
ranging from 3mm to 52.5cm in diameter. A few
applications are, enlargers, custom printers,
microscopes, endoscopes, telescopes, back projections of
all types. In these cases Beattie Intenscreen™ will provide
a better than twofold gain in light transmission over
conventional ground glass.
FOCUSING
& CAMERA FOCUS
Critical lens focus on the film
depends on installing the correct components in the correct
order. This should be determined at the time of ordering. The
installation should be tested on a fine line target with high
resolution film. If there is any doubt of the very short depth of
focus lenses are being used, it would pay to have the camera
checked on a collimator (Camerascreens will not be responsible
for any focus errors).
LIGHT
METERING
External meter and the modern
slide in meter sticks that meter the image in front of the screen
will not be altered. However, the Beattie Intenscreen™
is BRIGHTER.
If you use a meter with a fibre optic probe (like Gossen) or an
optical Type I spot meter (like Litemate\Spotmate by Photo
Research), then the absolute EV readings will be different from
any other screen, when you take readings off the eye side of the
cover plate. If you wish to compare relative bright\dark areas,
this works as before, but for absolute exposure, the direct meter
at the lens should be used.
FRESNEL
LENSES
The fresnel lenses on the back
of the focusing screen are a 6" effective focal length
plano convex lens for 6 x 9 and 4 x 5 view cameras and a
10.45" effective focal length plano convex lens for 5 x 7
and 8 x 10 view cameras, with convex portion towards the eye. For
optical calculations the fresnel side conjugates are 6" and
10.45", both plano side conjugates are infinity for the
fresnel lens with 6" EFL and 10.45" EFL, respectively.
These choices suit most of the normal view camera lenses.
Some points to consider: 1. If using a viewing attachment with a
mirror inverter, everything is OK. If there is a magnifier lens
included, it may cause vignetting and should be removed. 2. When
using short wide angle lenses (Super Angulon etc.) see use of
extra fresnel lens in the first part of this article. This is an
identical fresnel to the fresnel on the focusing screen except
it is installed with the plano convex side towards the other
fresnel. This makes a Ramsden pair, for least distortion, which
makes a combined focal length of about 3" which will cope
with lenses down to Super Angulon 47mm.
MISCELLANEOUS
INFORMATION
The acrylic set back, glass cover plate, and extra fresnel lens
are all .060" thick. The focusing screen are 0.075"
and 0.085" thick respectively. A few cameras, especially
older wooden framed ones may require slightly longer screws. Do
not over tighten clip screws when installing, especially when
using glass cover plates. This also allows for expansion and
contraction. |
