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Why Use a Matte Box?
Adding a matte box to your camera serves two
important functions – to block unwanted light from
hitting the lens causing lens flare, and to hold filters
that allow you to modify and enhance the image. Although
a rubber lens shade may block some of the light, its “one
size fits all” limits effectiveness. Matte boxes,
on the other hand, can be customized and adapted to get
the most out of their attributes.
The Chrosziel 16:9/4:3 mattebox kit for
the Canon XL H1
There are two types of Matte Boxes –
clamp-on and rod mount. A clamp-on is attached to the
camera by physically “clamping on” to the
front of the lens. These are normally lighter in weight
and very good for handholding the camera but are limited
in the number of filter holders and accessories that can
be added. A rod mount matte box is attached by sliding
it onto two parallel rods that have been mounted to the
camera. These rods can also hold other equipment such
as a follow-focus or a French flag. Some matte boxes even
have brackets that allow the shade to “swing away”
from the lens giving quick access to the lens itself -
a real time saver when swapping lenses. Both kinds of
matte boxes normally accept different size adapter rings
to accommodate a wide variety of lenses allowing the matte
box to “seal” to the lens. Without a seal
of some sort, extraneous light might enter from the sides
or rear and bounce off the filter back into the lens.
Chrosziel 602-01 MatteBox
with Swing Away
Popular sizes of matte boxes are 4x4,
4x5.6, and 5x5 – they’re labeled as such because
of the size of filters (dimensionally in inches) they
can accommodate - though many have “combo”
filter trays allowing smaller sizes of filters to be used.
Filters are placed into spring-loaded filter trays that
are inserted at the rear of the matte box and positioned
for the desired effect. Matte boxes have multiple filter
“stages” - some with stages that can rotate
individually, or, are even geared to move the filter precisely
during the shot. Individual stage rotation is especially
useful when using Neutral Density or Color grads allowing
the DP to adjust the angle of each filter for a specific
effect.
Accessories include the “eyebrow”
that pivots on the top of the sunshade, “wings”
or “ears” that pivot on the sides of the matte
box, an adjustable internal bellows, and snap on “hard
mattes” that attach to the front (these have varying
sizes of holes to coincide with a specific focal length).
All of these accessories are designed to sculpt the light
path as much as needed to effectively block errant light
and keep the lens free from flares and glares.
Sometimes, like when shooting cars at night with a filter(s)
in place, secondary reflections are generated as the light
bounces between the surface of the filter(s) and the front
element of the lens. You may not be able to do anything
about the origination of these kinds of internal reflections,
but what you can do is to attempt to move the reflection
off the lens and there are a couple of things you can
try. If you’re using a swing-away matte box, swing
it out slightly – it won’t take much to slide
that reflection out of the light path, but make sure to
anchor it so it doesn’t move unintentionally. If
your matte box has a rubber bellows back that fits against
the lens, attach a rubber band to the filter tray handle
and gently pull it so that the filter(s) are no longer
perpendicular to the lens. Again, the goal is to move
the reflection just enough to get it out of the frame.
But then, sometimes there’s just not a thing you
can do about it.
Okay, you’ve blocked the extraneous light –
how do you enhance the light that does reach the lens?
Filters, of course, but which one? The
choice of filters depends on what you’re trying
to achieve.
Different types of filters modify the light in their own
way. Knowing when and where to apply them is the key.
It is a good practice to first color balance to your lighting
conditions before adding filters, especially those that
are used for color alteration.
- Diffusion
– these are used to soften the image in varying
ways and come in different densities and materials
– glass, resin, nets, even the time honored
“Vaseline on the lens” trick. The most
popular are probably Tiffen’s ProMist and
Soft Effects filters. All manufactured diffusion
filters come in stepped amounts of diffusion - the
higher the number the heavier the effect, but, each
kind has it’s own gradient levels.
Photo courtesy: The Tiffen Company
Don’t be fooled into thinking that a #1 ProMist
diffuses the same amount as a #1 Soft Effects. Not
only is their effect different but they have different
densities, too. Generally speaking, a #1 ProMist
would be considered heavy while a #1 Soft Effects
would be a light amount of diffusion. |
Nets are “old school” diffusers that
not only diffuse the shot like no other filter, but, can
add a little sparkle if there are speculars in the frame.
The best location for a net is on the back of the lens
and the best way to mount it to a lens with a B4 mount
(the standard for full size cameras) is with an “i-Ring”.
This plastic ring holds a net tautly and slips onto the
back of the lens – very easy, very convenient, and
allows you to carry an assortment of nets safely. Avoid
putting nets on the front of the lens - even manufactured
ones by Tiffen, et al. The effect is not nearly as nice
as a rear mounted net and you run the risk of seeing the
pattern in your shot.
The best material for nets is women’s hose
– silk is tops but good luck finding any. Density,
material, and weave pattern is what determines the effect
(and the filter factor). A good way to see the effect
is to look through the net at a specular light source
- so bring a small flashlight with you when you go to
the mall and hang out in the women’s hosiery section.
Once you discover a net or two that you really like you’ll
understand why there is nothing more personal (and secretive)
in a DP’s arsenal of tools than their selection
of nets.
In addition to the density of diffuser you’re
using, the format you’re shooting will also play
a role in how much the effect comes across – the
smaller the target the more pronounced the effect with
the same filter. Using ProMists as an example, a 1/2 ProMist
on a 35mm motion picture camera with a “normal”
lens would show a light diffusing effect. Put that same
1/2 ProMist on a 1/3” chip camera at it’s
“normal” lens and the effect would be quite
pronounced. And if that wasn’t enough, the focal
length of the lens plays a major role, too. The longer
the lens, the heavier the effect, no matter the format.
And to add to the list, the type of lighting affects the
way a diffuser looks, also.
To sum up, the amount of diffusion that will
show on your image is based on the type of diffuser, the
grade of the diffuser, the format you’re shooting,
the focal length of the lens, and the way the scene is
lit. Complicated? Maybe at first, but as you use these
filters you’ll find a few that appeal to you and
the grades that work best the majority of the time. These
variables are why diffusion filters come in graded sets,
enabling the DP to match the effect scene to scene no
matter what.
Note: NEVER put Vaseline, or anything else, including
lens fluid, directly onto a lens. Doing so may allow liquid
to seep into the lens and adhere to an internal element
causing an expensive cleaning/repair. When cleaning a
lens, the cleaning fluid goes on the lens cloth. If you’re
intent on using Vaseline or some other medium, put it
on a clear filter instead.
| - Exposure
– these are Neutral Density (ND) filters –
filters that do not change the color of the scene,
they just lessen the amount of light hitting the
lens in precise increments. Unlike filter wheels
on a video camera with their designations for ND
amounts (1/4, 1/16, 1/64 for 2, 4, and 6 stops),
external filters’ nomenclature is .3, .6,
.9, 1.2, for 1 stop, 2 stop, 3 stop, and 4 stops
loss of light, respectively. In practice, we drop
the “point” and just say ND3, ND6, etc.
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Want to lessen the amount of apparent depth of
field in a shot to help isolate some part of the frame?
Adding an ND filter allows you to open
the iris on the lens to a lower stop lessening the depth
of field (remember, the higher the stop the more apparent
depth of field). ND’s can be stacked, too (an ND6
plus an ND9 = 5 stops of light loss), to get you down
to the stop you want.
Photo courtesy: The Tiffen Company
ND’s also come in grads - extremely useful
for parts of the frame that would normally be overexposed
– a hot sky, a white wall, snow in the foreground,
etc. Use them wherever you want to reduce the luminance
of some part of the frame – top, side, bottom, or
diagonally (remember me mentioning the importance of a
rotating stage on the matte box?). Grads come in the same
densities as full frame ND’s - 3, 6, 9, –
even soft and hard edges on the transition – but
unlike full ND’s – DO NOT ADJUST THE IRIS
AFTER YOU ADD AN ND GRAD! Opening the iris will not only
negate what you are trying to accomplish, it will also
overexpose the area not covered by the grad.
- Color alteration
– these are the fun ones. Give your shot that
old-time photo look by adding color overall with
a Sepia, intensify that sunset with a Sunset Grad,
or make that blue sky even bluer with a Blue grad.
These filters aren’t designed to correct or
compensate, only to allow you to accentuate one
or more colors.
Photo courtesy: The Tiffen Company
Depending on the filter you use, these will probably
be treated like ND Fulls and Grads (i.e., a full
color filter like a Sepia would need an iris adjustment,
a color grad would not).
Photo courtesy: The Tiffen Company
One very unique color filter is the Red Enhancer.
It’s uniqueness is that it only affects the
warmer colors like red, orange, and yellow. Want
your fall foliage to practically drip color? Put
on an Enhancer (just be careful if you have talent
in the shot – sometimes it affects skin tones
adversely).
- Effects – as the name implies
these filters impart an effect on the image –
the most common being star filters. Star filters
achieve their effect by lines etched onto one of
the glass elements – all you need is a specular
light source in your shot to show the effect of
refracting the light.
Photo courtesy: The Tiffen Company
Common versions produce symmetrical stars but when
the etched lines are asymmetrical the effect is
more “natural”. Two examples of these
are Tiffen’s Hollywood Star and Hyper Star.
When using any kind of star filter make sure you’re
not using a smaller aperture or that your lens is
too wide - either could show the etched lines on
the image. And, to be honest, star filters are quite
dated and unless there is a specific need for that
effect, should probably be avoided.
An effect type filter that is probably used
more than any other is the Polarizer. Affecting
only specific light waves, rotating it increases
or decreases the amount of polarization. Great for
reducing or even removing reflections and glare
from many surfaces - they’re even good for
“cleaning up” light skipping across,
believe it or not, skin. Over reflectance of any
skin type can be diminished with a Pola, particularly
noticeable on darker skin tones. And in addition,
a Pola also acts like an ND filter (normally about
2 stops) to help you with depth of field.
Photo courtesy: The Tiffen Company
What Polarizers are best known for though, are deepening
and enriching a blue sky. Maximum effect is attained
when you shoot 90 degrees to the sun (shooting toward
or away from the sun will have little to no effect
on the sky). What you want to avoid doing when using
a Pola is panning or tilting too many degrees, especially
panning. Depending on the focal length, you can
easily pan through the Polarizing effect, creating
a disturbing sky that changes in color and saturation.
- Focus – these include diopters
and split diopters. The diopter “lens”
is shaped like a magnifying glass that has been
slit in half, with one side curved and the other
flat. They come in different strengths (+1/2, +1,
+2, and +3 are the most common) and are mounted
on the front of the lens, curved side out. They
allow any lens to close focus, the higher the diopter
number, the closer the focus can be obtained. Need
a shot of a coin to fill the frame? Or letters being
typed on a computer screen? One way to achieve this
is with a longer lens and diopters. A +2 diopter
on a lens whose focus is set at 4 feet will now
be sharp at 14 inches. The key to diopters is using
the longest lens and the lowest power diopter that
is appropriate for the shot, plus stopping down
as much as possible because your depth of field
can be in fractions of an inch. Diopters degrade
the image, sometimes very noticeably, so be judicious
in their use. |
Split diopters (shaped like a half moon) work
like normal diopters but are designed to allow for both
very close and normal focus using one lens, mimicking
a deep focus effect. Besides the slight image degradation
mentioned previously, another downside is that there will
be a soft focus “line” from the edge of the
glass that has to be disguised in the scene – not
often done invisibly.
Some people believe that with the advanced technology
available in post that filter effects should be applied
electronically during the edit and not at the time of
acquisition. Although there may be validity to that in
some cases, there are also reasons not to:
- Many claim that adding
almost any kind of effect, especially diffusion,
introduces unnecessary noise to the image. Filters
on the camera don’t add noise – the
image created there is the cleanest it will ever
be.
- Software can do amazing things but it can’t
yet easily do what a Polarizer does when it comes
to diminishing reflections. Does it make sense to
spends hours in edit fixing what takes about 30
seconds to do at the shoot?
- And probably the strongest case against adding
the effect in post is that filters are applied in
the field for various technical reasons but just
as importantly, they’re introduced from an
emotional standpoint, too. They’re chosen
with as much thought as is given to where to place
a light. How much diffusion feels right? Will a
Tiffen 812 add to the scene? How does a particular
grad affect the mood of the shot? Every Director
of Photography answers these questions in their
own way by deciding (in collaboration with the Director)
how the image should look – this is their
vision and should not be subject to the whim of
someone in an edit suite. But that’s only
my opinion. |
Broadcast Rentals' full size Matte Box kits include 10
of the most popular filters including a Polarizer, ND
& Color Grads, and Diffusion. In addition, we have
matte boxes that fit DV cameras from Sony, Canon, and
Panasonic. More specialized filters are available so stop
by and see how a matte box, and the right filter, can
enhance your images.
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