Lens flaring can occur when a light source such as the sun or artificial lights, strikes the front of the lens at a certain angle and then bounces across different surfaces to produce glare in the image. Using additional filters in front of the lens can increase the chances of flaring. The effects of lens flares can wreak havoc on the final image. This includes halos and streaks of light or an overall decrease in image contrast. Decreased contrast may not be as detectable as lens flare, but it can seriously degrade the quality of the image. Although some contrast can be added in post production, with the higher compression of HDSLR video, it’s best to limit the amount of unnecessary post processing. A lens shade helps block direct light sources from hitting the lens or filters.
Many photography lenses come bundled with specially fitted lens shades that mount directly onto the front of the lens. These are good for blocking lens flare and limiting the risk of losing contrast in the image. It is also the most economical solution to prevent or limit lens flare, but does not offer the level of control of a matte box.
The difference between a regular lens shade and a matte box is that a matte box offers more light-sealing capabilities, as well as the option to use drop-in filters (on most models). Although screw-in filters are cheaper and more widely available, the drawback is that they come in specific sizes and can't be used on multiple lenses (only adapter rings). Switching lenses during a shoot can take more time if it’s necessary to swap filters and adapters from one lens to another. Drop-in filters also offer more creative options, such as the use of a graduated ND filter to position the transition at the right point in the frame (e.g. the horizon).
Sometimes, it's possible to clip a matte into the matte box so that the camera sees through a rectangular hole that’s just fractionally bigger than the frame — this is where the term “matte box” comes from. While this technique can greatly minimize flaring by reducing the visible part of the lens to exactly what is required to get the shot, the matte itself can act as a kind of external iris and reduce exposure, so testing and caution are necessary.
Size and Weight
Although it's important for a matte box to be sturdy, for many HDSLR users, being small and lightweight (the matte box, not the HDSLR users) is more important for keeping the overall weight and size of the rig to a minimum. Many of the available matte boxes were designed for larger cameras. If a lot of "run-and-gun" shooting is planned, make sure to use one of the light, smaller matte boxes. Keep in mind that for a lot of shoulder-mounted work, a light matte box is essential for keeping the front weight down—otherwise the operator’s arms will fatigue quickly. There are lighter-weight matte boxes that use more advanced materials such as carbon fiber, but these are more expensive. There will usually have to be a compromise between weight, size and/or price, but it's essential to know what aspects are more important to the needs at hand.
The matte box size can also limit the focal length of a lens that can be used with the matte box. If the matte box is too small, the edges of the matte box will appear in the image when using wider lenses.
It's important to consider the widest lens, as well as the largest front diameter lens that will be used with the matte box and then select accordingly.
The mounting of the matte box needs to be straightforward and secure, so it won’t fall off while the camera moves around. There are two main options for mounting the matte box to the lens: clipped directly to the front of the lens, or mounted on industry-standard rods, also called a "bayonet" mount. Clip-on matte boxes are usually smaller, weigh less and are less costly. The drawback of clip-on matte boxes is that they're not efficient for use on multiple lenses, especially different-diameter lenses, and can’t easily be used on external-focus lenses. Additionally, they're typically not as durable because they're made of lightweight materials. Some matte boxes offer both mounting options for maximum flexibility and offer a good balance of weight vs. function.
In order for the lens to align to the center of the matte box, the industry standard height from the base of the camera to the center of the lens needs to be 85mm. The SLR body was never designed for this purpose. When using a rod-mounted matte box, there may be a need to adjust the height of the matte box (depending on the camera, baseplate and attached accessories). Some matte boxes are too limited in their height adjustability to compensate for the offset of the lens. If plans call for adding accessories (e.g. battery grip, XLR adapter) under the camera body, this may cause a setup issue. The ideal is to have both an adjustable matte box and an adjustable baseplate to provide maximum flexibility and compatibility.
Filters are placed in the matte box with the use of filter trays. The trays need to be durable and latch onto the filters securely, so they don't fall out while being handled. In addition, some filter trays are designed to prevent light from bouncing or leaking through the edges.
There are two main types of trays: fixed and rotating. Rotating trays are used for graduated filters to align the horizon, or for polarizing filters, which must be rotated until the appropriate amount of reflection reduction is achieved. A good matte box will have at least one fixed and one rotating filter tray.
There are different standard-size filters. Matte boxes are designed for either a range of sizes or for one particular standard. While there are several standards of filter sizes, 4 x 5.65 is better suited to the 16:9 widescreen format. Larger sizes, of 5.65 x 5.65 or 6 x 6 are typically used for rotating filter stages. Certain filter trays can be adapted to accept different filter sizes.
Flags, or French flags, offer additional flare protection for addressing issues with specific light sources. The angle of the flag can be adjusted, usually by loosening a screw and re-tightening. The most common type is a top flag, but side flags are used for even greater control.
Mattes are designed to further reduce light leaks into the lens elements by masking the edges of the lens. The right size matte is determined by the aspect ratio of the video camera (e.g. 4:3, 16:9) as well as the angle of view of the lens being used. Many matte boxes come packaged with different-sized mattes.
When the matte box is clipped directly onto the lens without rods, step-down rings may be required to fit different lens diameters.
For "bayonet," or rod-mounted matte boxes, a donut is mounted between the matte box and tightly around the lens diameter so that no light can leak in, bounce around and cause lens flaring. Most matte boxes include several sizes of donuts that will fit a range of lens diameters. For external zoom, or external focus lenses, it may be better to use a donut that stretches to allow the front of the lens to extend and retract without falling out of the donut.
When time (or money) is of the essence, every additional task adds up quickly during a shoot. Changing lenses can be either a matter of seconds or minutes. While every setup is different, being able to swap lenses without loosening and/or dismounting the matte box is a very nice option.
Swing-away matte boxes are not directly mounted onto the rod system, but onto a hinge that mounts to the rods. This allows the matte box to be opened and closed like a door, without removing it from the rods. Some companies offer swing-away adapters that can turn their standard matte box into a swing-away version.