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LCD Screen
Magnifiers |
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When using a digital compact camera underwater, the LCD screen
on the back of the camera is usually the only practical viewfinder.
This creates a particular problem underwater for those, such
as the author, who need reading glasses or bifocals; and it is
conceivable that even those with good eyesight will benefit from
something which makes the LCD easier to see. This article offers
some suggestions on the subject of LCD magnifiers and the general
issues raised for divers who need glasses. |
Prescription lenses:
If you need glasses all the time, you should enquire at your
local dive store about diving masks with prescription lenses.
You might also consider using gas-permeable contact lenses, but
in this case you suffer the risk (albeit one which many divers
are prepared to take) that you might lose your lenses if you
flood your mask. If you just need reading glasses however, or
your normal prescription differs from you reading prescription,
these solutions will be unsatisfactory, because you won't be
able to focus on infinity with your reading lenses in place.
For this situation, you need some kind of auxiliary magnifying
glass, and the choice lies between placing a high-powered lens
close to the screen, or a low-powered lens close to the eye,
or an intermediate powered lens somewhere in between. |
Magnifying glasses:
The cheapest solution is to take a simple magnifying glass with
you when you dive. It is important however, to choose a magnifier
with a glass lens. The difference in refractive index
between a plastic lens and water is usually very small, which
means that the lens will lose most of its magnifying power when
immersed in water. A glass lens will still lose about 2/3 of
its magnifying power, but may have enough left to be useful.
You should also ensure that the magnifying glass you adopt has
a plastic, aluminium, or plated-brass lensholder and handle (not
steel - check with a magnet), so that it will not corrode;
and you should use a single-element lens so that water does not
leak into any air-space or attack the bonding material between
cemented elements.
A cheap Sherlock Holmes type magnifier, with a plastic holder,
can be bought at a local market for about UK£1.50 (US$2).
A crown-glass lens can be identified by the slight greenish tinge
and the weight. The magnifying power can easily be estimated
by focusing an image of a distant object onto a surface (caution,
fire and burns hazard if you use the sun). The distance between
the lens and the image is the focal length of the lens. The reciprocal
of the focal length in metres is the power of the lens in diopters,
e.g., if the focal length is about 0.33m, the power is 1/0.33
= 3 diopters (fairly typical for magnifying glasses). Such a
lens immersed in water will usually have a power of a little
over 1 diopter (it depends on the type of glass), roughly equivalent
to a typical reading-glass prescription when held close to the
outside of your diving mask. A hole drilled in the handle will
allow you to attach a lanyard and clip it to your buoyancy jacket.
The dissatisfaction with using a separate magnifying glass, is
that it requires an extra hand in order to hold it. If you wear
a helmet to carry torches, you might consider attaching the magnifier
to the helmet and improvising a swivel-joint so that the lens
can be flipped in front of the eye when needed. It all adds encumbrance
however, and the best solution for LCD viewing is obviously to
attach something to the housing. |
Close-up lenses:
If a lens is to be placed close to the housing, it must have
a high magnifying power; and if this is to be achieved with a
single piece of glass, a high degree of curvature is required.
Such high-curvature lenses can be obtained by dismantling the
condensers from old enlargers and projectors, but the point of
this investigation was to find a solution involving commercially
available items. It was for that reason that the author's attention
fell upon the various underwater close-up lenses on offer, with
the most promising candidates being the INON
UCL-165M67 and the UN PCU-01. |
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The UCL-165 is a two-element lens with a sealed intermediate
air-space. Since most of the magnification is provided by the
two internal glass-air boundaries, the lens retains most of its
power when immersed in water. The power in air is +7.4 diopters,
and the power underwater is +6 diopters. Other close-up lenses
will work of course, but the viewing aperture of the INON lens
is a very generous 52mm, which makes it possible to us it as
a highly effective long-eye-relief viewfinder. |
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The author's test setup is shown below. The lens carrier consists
of an M67 lensholder ring from an Epoque lens-mount adapter bolted
to an Ultralight AD-SS YS-mount strobe adapter. This is attached
to the housing by means of a short ball-joint arm, which is mounted
on the housing top accessory shoe in the example given. |
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The author's reading glass prescription is +1.75 diopters. It
was found that the UCL-165 lens gave optimum results when placed
about 10 - 12 cm from the back of the housing and used with the
eye fairly close to it. With this arrangement, it was possible
to resolve the matrix of pixels in the LCD with excellent eye-relief,
the experience being very much like using an SLR camera with
an action-finder. The practical benefits of the magnifier were
immediately obvious: these being an increase in speed of framing,
elimination of composition errors, elimination of failed photographs
due to inability to read menus and error messages, and elimination
of fatigue due to eye-strain.
In the photographs above, the ball-arm on which the magnifier
is mounted uses an Ultralight AD-HS accessory-shoe mount, and
an Ultralight DB-03 (3" between ball centres) double-ball
arm section . The clamps give a distance of 1.5" between
ball centres, and so the distance from the centre of the accessory-shoe
ball to the centre of the lensholder ball is 6" (about 15cm).
This extreme extension of the arm is ideal for the author's eyesight;
but more latitude of distance adjustment can be obtained by using
the Ikelite #0466.42 double-ball arm section, which gives 4"
between ball centres and hence allows an adjustment range of
about 2 - 7" (5.1 - 17.8cm). Since the focal length of the
INON close-up lens is 165mm, a distance of 16.5cm from the mid-plane
of the lens to the apparent position of the LCD will cause the
viewfinder image to be sharp when the eye is focused at infinity,
i.e., the extreme extension obtainable with the 4" double-ball
is about right for those whose eyes have no accommodation at
all.
The arrangement shown is, of course, only suitable for housings
with an accessory shoe. In other cases it is possible to attach
an auxiliary ball-mount to the tray, handle, or housing, and
make up a ball arm suitable for the specific application. The
point (if using the UCL-165) is to mount the lens somewhere between
about 8 and 16.5cm from the LCD screen. Additional articulation
(another clamp and another double-ball section) may be needed
in some situations. Ultralight and Ikelite make suitable arm
components. |
UN LCD Magnifier
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Since the original version of this article was written, UN has
produced an LCD magnifier for the Olympus PT-series underwater
housings. |
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UA-9001
Fits Olympus PT-015, 17, 19, 20, 21, 22, 23, 24, 27.
 12.5 Diopters
in air.
Anti-reflection
coating.
Rubber hood.
Safety lanyard.
Dimensions /mm: 49h, 58w,
73d
Weight: 61g |
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UA-9001AP-1 Adapter allows UA-9001 to fit to Olympus PT-014,
16, 18 |
UA-9001 fitted to Olympus PT-020 housing.
DWK. June 2004 - April 2006.
Acknowledgement: Thanks to Dr Jonathan M Knights for suggesting
the Xtend-aView magnifier.
Photographs © Cameras Underwater 2004. |
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