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Close-up
photography - why is it so easy?
by
Peter Rowlands
Reproduced
from in focus 58 (September
1996)
Close-ups
are by far the simplest and most effective form of underwater
photography. As discussed in the article on basics, the three
main variables you have to get right for a technically correct
photograph are:
1.
Focus.
2.
Shutter speed.
3.
Aperture.
Close-ups
are so simple because, in most cases, you can preset and forget
the first two of the these variables and the third doesn't
have to be altered too much. If you've already got a TTL camera
and flash system, you don't have to worry about the third!
Electronic
flash is essential to restore the colour and detail in your
subject and, in most situations, provides the total light
for the exposure so no allowance needs to be made for available
light.
For
simplicity's sake, the flash position should be fixed to simplify
exposures.
The
first two 'variables' which can be preset are:
1.
Shutter speed
The
maximum Shutter speed you can use is governed by the electronic
flash and, on the Nikonos IVa and V, it is 1/90th sec but
because the flash is providing all the light for the exposure,
the Shutter speed is almost irrelevant, even with cameras
which can be used with a higher Shutter speed.
Preset
the Shutter speed to the fastest setting your camera will
allow for electronic flash and forget it. Using a slower Shutter speed will make virtually no difference to the exposure.
2.
Focus
With
Nikonos close-up equipment such as close-up lenses or extension
tubes, the focus is preset to make sure you are in focus where
the frames indicate.
Altering
the focus will in fact make little diflerence to the focus
position but don't complicate things.
Preset
the focus according to the manufacturer's instructions and
forget it.
With
reflex cameras you will be able to see the exact point of
focus so you will not have to worry about correct focus.
3.
Aperture
Because
the flash is providing all the light for the exposure, the
only variable to get right is the aperture.
If
you are using a TTL camera and flash system such as the Nikonos
V or Motormarine 11, the internal electronics will even adjust
the light output for you -regardless of the you use.
To
understand the importance of selecting the right aperture
let's assume we're using a manual flashgun so we have to set
the aperture to get the right exposure.
When
working at such small flash-to-subject distances, the guide number method (guide number/flash to subject distance _ aperture)
of calculating the correct exposure basically still applies
but in practice it's better to do a trial and error test.
This
involves taking identical shots but varying the aperture from
f2.8 down to f22.
The
resulting slides will show the correct aperture for that type
of subject. With close-ups, you won't need to go through the
whole aperture range because the wider apertures will most
certainly be overexposed so bracket your first shots from
fl 1 to f22 to find the correct one for the tone of subject
you are photographing.
The
exact aperture will vary depending on the tone or reflectance
of the subject so repeat this test on three subjects of differing
reflectance such as a white sea urchin or starfish, a neutral
tone subject such as a light green kelp and a dark subject
such as a sea cucumber.
Having
done this simple test, you are set up to take 36 out of 36
perfectly exposed frames per film and you only need to alter
the aperture to take the reflectance of the subject into account.
Close-up
equipment for non-reflex cameras
Two
main devices enable the standard lens on a Nikonos or Motormarine
II to focus closer than normal.
1.
Close-up lenses
These
optical devices are placed in front of the prime lens and
enable them to focus closer - usually about 10 inches in front
of the lens. They can be taken on and ofil underwater which
gives useful versatility.
2. Extension tubes
These physical devices have no optics but just place the prime
lens further away from the film. They are only available for
Nikonos cameras. They must never be changed underwater.
In
theory, the further away a lens is from the film, the more
light will be needed to get the right exposure but, in practice,
because the flash to subject distances get smaller the longer
the extension tube you use, the effect is thankfully virtually
counteractive.
Extension
tubes bring you into focus much closer than close-up lenses.
Reproduction
ratios
In
order to quantify the performance of close-up devices (extension
tubes in particular) the frame area covered is compared to
the 35 mm film frame size.
A
1: 1 extension tube will take pictures of subjects the same
size as the 35 mm frame, ie 24 x 36mm.
A 1:2 extension tube will take pictures of subjects four times
the area of the 35 mm frame, ie 48 x 72mm.
A 1:3 extension tube will take pictures of subjects nine times
the area of the 35 mm frame, ie 72 x 108mm.
A 2:1 extension tube will take pictures of subjects half the
size of the 35 mm frame, ie 12 x 18mm.
Reflex
viewing
For
those underwater photographers who use a land camera in a
housing (or a Nikonos RS) you will be able to have the versatility
of a macro lens which lets you focus on anything from infinity
down to around 6in from the lens.
The
first two variables of Shutter speed and focus are still not
a problem but, since the flash to subject distances are going
to vary considerably, so too will the aperture.
As
before, if you're using a TTL system, the correct exposure
will be sorted out for you by the system's electronics but,
for manual exposure systems, you will have to set the correct
aperture.
To
simplify what can be a difficult area, it is best to mount
the flash over the subject and forward of the camera so that
the flash to subject distance doesn't vary much, even though
the camera to subject distance varies considerably.
The
big advantage of a reflex camera system is being able to see
the exact point of focus through the lens as well as being
able to frame the subject to your complete satisfaction.
Reproduced
from in focus 58 (September
1996) |
