Sony NEX-EA50 NXCAM Handbook page 13

External ND filter
When using a wide aperture in a bright outdoor setting, for instance to achieve a shallow depth of field effect, a high shutter speed is
required in order to prevent overexposure. Where a shutter speed of 1/48 sec would be suitable in 24 p mode, at a larger aperture a
very fast shutter speed of around 1/1000 sec would be needed, making movements appear brittle and unnatural. An alternative is
to fit an external ND filter to the lens to reduce the amount of light entering the camera.
■ Round, glass screw-in type
These filters are designed to be screwed in at the tip of the lens
unit. Cheap and widely available, these filters can reduce the light
volume to 1/4, 1/8, or 1/16 of the original level.
Because they need to match the lens unit's filter diameter
requirement, you need to obtain filters that are in the right size or
alter the filter diameter by using a tool such as a step-up ring.
If the light volume is still too high even with a 1/16 filter,
you will need to combine multiple filters. In such instances,
diffused reflections can easily cause flares and halation. To
prevent them, you need to block the light from directly hitting
the filters.
■ Sheet type
Because these filers were at first based on gelatin, they are still
widely referred to as gelatin filters.
They are inserted into a paper filter-holder. Sometimes, they are
cut up into smaller pieces and attached to the back of the lens or
the lens mount. You need to be careful with dust and make sure
that pieces of the sheet-type
filter do not touch the sensor
section. For these reasons, we
do not recommend the second
usage method.
How to select ND filters
TIPS
If you normally use two or three lenses, we recommend getting 1/4, 1/8 and 1/16 round, glass screw-in type ND filters that match
the diameter of your largest-diameter lens. Or it could be a fader-type ND filter that matches the diameter of your largest-diameter
lens. When you use a smaller lens, you can attach your filter to a step-up ring.
If you use many lenses and they include a large-diameter lens, selecting the combination of a matte box and square glass ND filters
will give you more flexibility.
■ Filters that enable ND level to be controlled
via fader lever
These recently introduced products are round, glass screw-
in type filters with a lever on their outer circumference. By
turning the lever, you can change the light volume.
These filters alter colors more than other types of ND filters.
You need to take precautions, such as checking white
balance manually for every cut.
■ Square glass type
These are high-priced filters that are used in combination with a
matte box. They are not affected by the lens diameter, and the
light volume can be adjusted by simply changing one filter with
another.
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