Dive Pacific 171 Oct- Nov 2019

define sensitivity: the higher
the number, the higher the
sensitivity. The number
always follows the ISO abbreviation.
Consecutive sensitivity
values
Every time when the sensitivity
value doubles, the
sensor requires two times
less light to correctly expose
an image. For example,
ISO400 would require two
times less light than ISO 200
and four times less light than
ISO100.
Whole sensitivity values are
100, 200, 400, 800, 1600, 3200,
etc. There are also fractional
values between them at 1/3
and 2/3 steps. In the past,
during the camera film era, a
correct choice of film determined
whether your photo
shoot would be a success or
a failure. Now, the choice
of the sensor sensitivity is a
matter of a few seconds: all
you need to do is press the
proper buttons and voila!
The viewfinder
A viewfinder allows a photographer
to see a future image,
compose it, and assess the focus.
For an underwater photographer it
is of a paramount importance! You
need to be able to see well through
the viewfinder.
Modern cameras use two types of
viewfinders: liquid crystal display
(LCD) in compact cameras and
mirrorless camera, and mirror
reflex optical viewfinders on DSLR
cameras. The mirrorless cameras
have an electronic analogue of the
optical specular viewfinder which
are very similar to the viewfinder
of an ordinary DSLR, and even
better.
At first glance the large LCD screen
of a compact camera is more
convenient than a mirror reflex
viewfinder. For example you see
an interesting subject under a
coral (where you don’t fit) but can
easily place your camera there.
You look at the screen at arm’s
length, frame the image and shoot!
However…
The mirror reflex optical
Shag Rock, Goat Island Marine Reserve, NZ
Olympus Tg-4 on 25 mm with wide lens
PTWC-01 (f2,8;1/200; ISO100)
Olympus PT-056 housing
Nauticam with mirrorless Olympus.
viewfinder more than makes up for
any drawbacks. With it:
1) Even in the brightest conditions
you can see a clear picture of the
image. It gives you the possibility
to easily frame your image and
assess its sharpness.
2) There is no shutter lag. As soon
as the subject is framed and in
focus, the shutter opens up instantaneously.
3) It doesn’t matter whether you
are short sighted or farsighted: all
modern reflex cameras have a +/-
diopter adjustment option. You can
see everything clearly and sharp.
4) An electronic “mirror”
viewfinder mirrorless (also called
optical), allows you to see right in
the shot.
Special adapters can be used to
install a third-party 45-angled
viewfinder on almost all housing
models. For example, I was able to
install an Inon viewfinder on my
Ikelite housings and am now using
a similar viewfinder by Nauticam
with mirrorless Olympus.
But to use all the advantages
of a mirror (optical)
viewfinder you need to learn
how to use it well. So:
1) Use low-volume masks!
A one-window mask would
not allow you to bring your
eye close enough to the
viewfinder to be able to see
the whole field of the frame.
2) Press the housing
viewfinder to the mask
window. Don’t be afraid! This
is the only way you can see
the whole frame.
3) Learn to look through the
viewfinder properly. Because
you are looking through it
with one eye, the first thing
you see is the central part of
the frame. If you don’t take
your time, you could end up
with things in your image not
supposed to be there. Before
pressing the shutter, look
around the whole frame. Pay
special attention along its
perimeter. So, first the centre,
then the edges, then press the
shutter button!
4) To make it easier to focus,
some housing manufacturers
produce magnifying viewfinders.
These can be used even by divers
with full-face masks. There are
straight and angled types of
magnifying viewfinders, and when
you use an angled viewfinder, you
don’t look straight through it but
rather at a 45-degree angle and
slightly downwards. They are very
helpful when you are shooting
close to the seabed, from top down
or taking above and below (splitlevel)
shots. Some models can be
adjusted to change the angle of
the viewfinder. The only disadvantage
of such viewfinders is their
relatively high price.
Next time: ISO, exposure and other
underwater “spices”
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