Digital Photography 101
Chapter 2: Detachable SLR Lenses and when to use them
2.4: Filters
There are a few essential lens filters a photographer needs to
keep in his or her kit. The conversion filters used to adapt daylight
balanced film to prevent colour casting are no longer necessary
if you are using a modern digital camera which will compensate white
balance. See chapter 1 for details. Instead we have seen the opposite
become attractive with the use of coloured filters to purposely
change the colour casting for artistic creativity. Using a red or
warm up filter we can turn a daylight seascape into the warm glow
of a sunset as an example among many effects. All of the filter
effects can be achieved in Photoshop but my attitude is to do as
much you can in camera to save computer time later.
UV filters
Ultra violet filters will aid in reducing haze in landscape photography
but the primary use of this less expensive filter is to protect
the expensive front lens element and you should keep it fitted at
all times unless you are using other filters. A UV filter will block
some light but not enough to be an issue on most lenses. If you
are using a UV filter on a cheaper long lens then I do suggest you
remove it in low light so you can get as much light into the lens
as possible. In short the front lens element of any lens can easily
be damaged, even by simple wear and tear, so keep that lens cap
on when your camera is not in use and fit a UV filter, unless it
is absolutely necessary for extra light.
Polarizing filters
You may have heard of polarizing sunglasses, which fishermen are
fond of, because they enable them to remove reflections and see
into the water? Well in photography the removal of unwanted reflections
can be of a great advantage. A Polarizing filter consists of two
elements, the front one being able to rotate to either increase
or decrease the effect. This is the circular filter, which is popular
on today's lenses. Looking through the lens in an SLR camera you
can see the reflections in water and on shiny surfaces disappear
before your eyes as you rotate the outer element. I use this filter
when I photograph cars and trucks but this is not the only use.
A polarizing filter will saturate colour, especially in the greens
and the blues making for highly contrasting deep blue sky in landscape
photographs. It is important to note that the effects of a polarizing
filter is increased when shooting to its maximum at 90 degrees from
the sun and is at its minimum facing into the sun or to your back
to the sun. This filter will block about two stops of light, so
don't use it unless you need and don't keep it fitted to the lens
as a default. Don't double up a polarising filter and a UV filter.
Neutral Density Filters
This is a grey filter, which will not change the colour, but it
will stop down the light getting into the lens and therefore slow
down the shutter speed or making larger apertures possible to shallow
the depth of field. So why would you want to do this? Sometimes
there is just too much light to create a desired effect of movement
and waterfalls are a good example of this. The motion blur from
moving water is a desired effect and can only be achieved at shutter
speeds of below 20th of a second depending on the speed of the water.
If the waterfall is in a bright place then over exposure will be
the only outcome even at a very narrow aperture (f22) This filter
is like putting sunglasses on. Don't forget to use a tripod below
60th of a second to prevent shudder blur.
Neutral Density Graduated filters or ND Grad filters
Similar to the graduated filters but this filter only covers half
of the diameter with the bottom half remaining clear UV glass. They
come in three degrees of intensity with a standard grad filter being
the most versatile.
Where to use them? Landscapes primarily, as the affect is to cut
the exposure in two parts. The top will filter down the light creating
a correctly exposed sky and the bottom half will let more light
through to correctly expose the foreground. Making for a much more
natural composition, similar to how the eye would see it.
Filters can make all the difference to your photography and will
become an essential part of your kit. A good tip is to have a soft
blower brush on hand to gently remove unwanted dust from filters
and lens element as you attach them and make sure you buy filters
that will fit your lens, as the there are many size variations.
Also don't stack your lenses on top of each other as this will create
vignette or tunnel view at wide angles and stop lots of light required
for a faster shutter speed. Clean your filters and lens elements
with an approved solution and a clean purpose made cloth and ensure
your hands are clean, holding them from the outer edge. Did I really
need to say that?
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