the film naturally appeared you had to alter the light before
it was recorded. Want a warm cast? Add a Wratten 81C filter
which has a medium-strong ‘straw’ coloured tint to the front of
your lens. To cool down a photo, add an 82B. If you needed to
use daylight film indoors use an 80A filter.
Obviously all of these adjustments can now be done either in-
camera by changing the camera’s white balance setting, or you can
easily do it in-post if shooting raw. So in the case of colour correction
filters, no, I do not use these any more since there is literally no point.
Having said that, physically modifying the light before it hits
the film (or sensor) has certain other advantages which do not
have a post-processing analogy. These include:
- Changing the amount of light entering the lens – Neutral
Density (ND) filters. - Reducing the amount of light from the top of the picture
relative to the bottom part – Graduated NDs. - Reducing the levels of polarised light entering the lens –
Polarising Filters.
This is the key to thinking about filters – should you modify
the light first or modify the capture afterwards.
Neutral density filters
Neutral density (ND) filters are designed to absorb light and
extend exposure times. They come in various strengths – one
stop (x2 or 0.3), two stops (x4 or 0.6) etc. For extremely long
exposures you can buy strong ND filters that absorb 10 (ND400)
or even 16 stops of light so you can shoot very long exposures in
daylight for creative effect.
Really long exposures are excellent for blurring slowly
moving subjects like clouds and water. Normally you need to
wait until it gets dark to be able to use long enough exposures
so that the movement is recorded, but using a strong ND can
allow you to ‘force’ long exposures even in full daylight. For
example, a 10 stop ND will change the exposure from 1/60s at
f/16 (full sunlight) to 15s at f/16, long enough for water to go
nice and blurry.
There is no way to precisely emulate the effect of genuine long
exposures in-post. It is possible to get close using Stack Modes on
multiple shots in Photoshop, but it’s never quite the same.
There is another use for ND filters that makes them almost
indispensable, and that is controlling depth of field for video.AUSTRALIANPHOTOGRAPHY.COM 43
HOW TO Which Filter?
ABOVE
Lusancay Islands,
PNG. A polariser
has made the
water wonderfully
translucent.
Canon EOS 5D,
17-40mm f4L lens
@ 17mm, 1/250s
@ f9.5, ISO 200.AUSTRALIAN PHOTOGRAPHY MARCH 2016