Series editors' preface - Wood Tools

• Availability of adaptors for close-up work
and attachment to microscope if required.
• Cost.
Control of the amount of light falling on the
film can be effected by changing the lens aperture
and by changing shutter speed. To achieve
a given exposure, as the shutter speed increases
the size of the aperture will need to be
increased. Conversely, a reduction in shutter
speed allows the lens aperture to be reduced or
‘stopped down’. Reducing the shutter speed
affects the sharpness of objects in motion and
renders the effects of camera shake more likely.
Changing the lens aperture affects depth of
field, contrast and definition. The depth of field,
the distance in front and behind the subject that
will be in focus, increases with smaller apertures.
Since depth of field increases as we move
further away from the object, a useful guide is
to focus slightly behind the near parts of object.
Using small apertures gives sharper definition
as this effectively makes use of the centre of the
lens. As more of the lens is used, picture quality
may begin to degrade.
Single lens reflex cameras and other
through-the-lens metering systems have advantages
for routine determination of correct
exposures but are not infallible under all circumstances.
For very long exposures a TTL
meter will not work satisfactorily and a separate
light meter needs to be used. The colour of
the background has an important effect on the
exposure determined by a TTL meter of an
object placed against it. An object placed
against a white background will tend to come
out underexposed if the meter reading is followed
(therefore have to give more exposure,
1 ⁄2 to 2 stops). A light object on a dark background
will tend to come out overexposed and
should therefore be given less exposure. It is a
good idea to work out two positions of compensation
– one moderate and one more
extreme and to record all such experiments
while becoming familiar with equipment and
circumstances. The technique of taking the
same shot using a range of different exposures
above and below the theoretically correct
exposure is referred to as bracketing.
The Reciprocity law (Chapter 6) applies especially
to colour films. For example, for Kodak
Ektachrome, over the range 1/1000 second to
1/100 second the relationship between light
Conservation preliminaries 407
level and response of the film is linear. At 1/20
second response is within an acceptable range
but at light levels theoretically requiring a 1 second
exposure it is necessary to increase aperture
by one stop and use a 15B filter to obtain
a correct result. At 10 seconds a 1 1 ⁄2 stop compensation
and use of 20B filter are required.
Close-ups can be taken using close up
lenses, macro lens, extension tubes or bellows.
A 100 mm lens on bellows will go from infinity
to extreme close up and is therefore potentially
a very useful set up. It is the viewpoint
that determines perspective but the lens that
determines the viewpoint. Viewpoint governing
perspective becomes weird if too close to
objects. A long focus lens (say 100 mm on a
35 mm SLR camera), though it may have limited
actual close focusing, may be preferable in
achieving the effect of making the chosen subject
appear larger on film without the apparent
distortion that can occur by actually going in
close to an object. Alternatively, adjustable tilt
and swing lenses available for some cameras
(view cameras especially – 35 mm cameras are
rather limited in this respect) can be used to
compensate for the apparent distortion caused
by taking shots close up. Some close-up equipment,
such as bellows and extension tubes, has
a marked effect on exposure. The square of
the distance from the film to the nodal point
of the lens system (approximately the centre of
the lens barrel) divided by the focal length
of the lens gives the factor by which exposure
must be increased (unless using TTL).
9.5 Studio organization and layout
The basic requirements of any furniture conservation
studio or workshop space are to provide
a safe and secure environment for the
objects being worked on, to provide a safe and
comfortable environment for the conservators
doing the work and to provide a space that is
suitable to effectively and efficiently carry out
the work required. To achieve this, a great deal
of careful thought and planning is needed,
every aspect of which should be driven by the
work that will be carried out and by the needs
of people to carry it out. This section therefore
starts with a basic outline of the main
processes and procedures generally involved
in a furniture conservation commission. Useful