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Interchangeable
Mixing Chambers
The function of the mixing chamber of the C760
Dichroic Lamphouse is to combine the light from any
combination of the three dichroic filters — Cyan,
Magenta, and Yellow — to produce a uniform "mixed"
light of the desired filtration. The mixing chambers for
the diffusion lamphouse serve the same function
when using the optional variable contrast filters
designed for use in the attenuator slot. The light is
then passed through the film (color negative or
transparency or black and white negative) to produce
the exposure on the paper.
Two mixing chambers are supplied with your C760
Dichroic and Diffusion Lamphouses. The first is a
35mm chamber used when printing 35mm and smaller
negatives. The second is a 6x7cm chamber for print-
ing medium-format negatives: 4.5x6cm (1-5/8"x2-1/4");
6x6cm (2%" square); 6x7cm (2%4"'x2%"').
C760 Lamphouses use mixing chambers made of a
special polystyrene material that has been found to
provide optimum reflection and diffusion. In addition,
special patented tapered diffusers are used to further
increase the efficiency of the mixing chambers. As a
result, the C760 Lamphouse provides unsurpassed
evenness of illumination and high light output for
conveniently short printing times.
The mixing chambers are somewhat delicate and
should be handled with care, in particular, avoiding
excess pressure on the sides of the chamber. The
C760 Lamphouse comes with the 35mm mixing
chamber and tapered diffuser pre-assembled and
installed in the lamphouse. The 6x7cm chamber is
pre-assembled but packed separately.
To change the mixing chamber, simply unscrew the
metal knurled knob on the top of the lamphouse and
remove the lamphouse cover. Make sure that the
white light lever is in the 'off'? position and there is
no attenuator in the attenuator slot. This is done by
lifting from the back and tilting the cover plate
slightly forward. The mixing chamber can then be
lifted out and replaced by the alternative size. For
easy insertion, tilt the mixing chamber until it slides
easily into place. The chamber will automatically seat
itself properly for correct alignment. Make sure,
however, that the circular opening of the mixing
chamber through which the light must pass is
correctly positioned facing the quartz halogen lamp. If
the chamber is reversed, the opening will be hidden
and very little light will pass through. Be careful not
to press on the chamber housing too strongly.
12
If desired, additional filters can be added to the inside
of the mixing chamber for special effects.
To remove the tapered diffuser, simply depress the
sides of the mixing chamber just above the diffuser
holder and carefully remove the diffuser from the
holder. When inserting filters, place the tapered
diffuser in the holder upside down so that the filter
rests on a flat surface.
Using the Light Attenuators
There are times when it might be necessary to reduce
the amount of light being transmitted to the paper
without either reducing the lens aperture or shorten-
ing exposure times. In such a case, the C760 Lamp-
house utilizes light attenuators which physically
reduce output.
Three different light attenuators are supplied with the
C760 Dichroic Lamphouse. They are available as an
optional accessory for the C760 Diffusion Lamphouse.
The use of these attenuators does not measurably
affect the filtration, only the amount of light.
The reducing power of the light attenuator is
indicated by the number on the top edge of the unit.
Strengths of the three attenuators are:
EV Indication
Transmitted Light
a
50% (of normal)
-2
25%
3
12%2%
White Light Control
For ease in focusing and composing your picture on
the baseboard, the C760 Dichroic Lamphouse
incorporates a White Light Lever which removes the
filters from the light path so that only white light is
transmitted.
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