Comprehensive Ophthalmology Free Papers - aioseducation

70th AIOC Proceedings, Cochin 2012
Camera Controls
ISO: The ISO represents the sensitivity of the film or sensor to light. Normally
the option given is auto ISO, 100, 200, 400, 800, 1600 and rarely 3200 or more.
The higher the number, the more sensitive is the ability to capture the image.
As you increase the ISO, pictures can be taken at low light conditions. This will
produce a graininess of the picture. Hence for slit lamp photography set the
ISO always 100 or 200 or maximum at 400.
White Balance
This feature deals with the type of light used for lighting the object photographed.
To be more precise it means the color temperature of the light falling on the object.
The options available in a compact digital camera is auto white balance, day light,
cloudy, fluorescent under natural white light, incandescent light and flash. In
auto white balance setting the camera tries to recognize the color temperature
of the light falling on the object and sets the white balance. Incandescent white
balance is when the light source is an ordinary bulb or a Halogen light. As most
of the slit lamps use the Halogen bulb as the light source, this is the white balance
to be used for slit lamp photography. Flash can be used for gross photography
of the eye and the face. Otherwise while taking photos, the slit lamp is used as
the source of the light and magnification, hence the white balance to be used
is always incandescent light.
Focus
The compact digital cameras give option of multiple auto focus points and
central auto focus point. In the multi auto focus points the camera tries to
focus on the entire exposed screen. In case of central auto focus the camera
focuses only at the centre of the object in front of the camera. In case of slit
lamp photography it is better to use the central auto focus mode keeping
the area of interest right at the centre of the frame. In case of taking general
photograph of eye or face one can use multi auto focus mode.
Metering Mode
Most compact digital cameras provide at least 3 metering modes. Metering
mode means the exposure time to capture the image. This exposure time
is decided by two main factors, the shutter speed and aperture. Three to be
precise, the ISO, shutter speed and aperture. The shutter speed is the amount
of time the aperture remains open to capture the image. The lower the shutter
speed the more is the exposure, faster the shutter speed lesser is the exposure.
Aperture is the size of the opening through which the light reaches the film
or the sensor. The aperture is otherwise called F stop. The larger the aperture
the more the exposure, the smaller the aperture the less is the exposure. The
aperture is designated as 1.2, 1.8, 2.8, 3, 3.5, 4….22. The lower the number is
the larger aperture and the larger the number the narrower the aperture. The
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