ARRI ALEXA SUP 7.0, Pocket Manual, Page: 26 / 100

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While traditional ND filters work great for film, for
digital cameras we recommend the use of ND filters
that have a built-in far-red blocker. Such filters are
available from a number of manufacturers, often
called “ND filters with an IR-cut off”. A single filter
that combines a ND and a far-red cut off generally
yields better results and fewer reflections than a
traditional ND filter stacked on top of a separate IR
cut off filter.
While the close match between ALEXA’s custom
designed IR filter and the sensor’s spectral response
makes this issue less critical than with some other
digital cameras, it is generally a good idea to only
use traditional film ND filters up to an ND 0.9.
The ALEXA Studio has a built-in ND filter with a
density of ND 1.3 (4.3 stops), which can be moved in
and out of the optical path. The advantage over
classical ND filters is that it is located behind the
mirror shutter, so the optical viewfinder image stays
bright. While not blocking all the IR energy a com-
mercial Infrared blocker would, the Infrared blocking
abilities of the ALEXA Studio’s internal ND filter are
sufficient for most situations.
Working with ND filters