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MillimeterShoot Expertise: Camera Filters
Feb 1, 2008 12:00 PM, By Barry Braverman
Guidelines for deciding when to get physical.
By reducing scatter and darkening the sky in daylight scenes, a properly oriented polarizer will make any lens look cleaner and sharper—a key consideration in an era of underpowered optics affixed to cameras with high-resolution imagers. The enhanced contrast in scenes such as this one can increase apparent detail in the captured image. If not captured in-camera, such detail is lost forever.
As savvy digital shooters, we've all faced the dilemma: When is a physical camera filter required to achieve a desired look, and when is it more appropriate to use software to achieve the desired effect? It's not an easy question to answer, but in general, we can follow a few basic guidelines.
The foremost point to bear in mind is that image detail not captured in the first place (in-camera) cannot be restored later. Thus, it can be said that a physical filter that enables capture of greater image detail is usually desirable. From a shooter's perspective, therefore, the most important filter in your arsenal may be the polarizer — which, by darkening the sky and clouds and by reducing glare, can dramatically increase the amount of detail reaching the imager and ultimately your recording medium.
For most video applications, the linear-type polarizer is adequate. For autofocus cameras, a circular polarizer with the proper side facing the lens is required. Pictured: the Schneider Optics Circular Polarizer
The polarizer is the only camera filter that can increase actual contrast, and thus, it should always be considered when shooting daylight exteriors. The polarizer can be especially useful when shooting with the popular prosumer cameras, which invariably feature mediocre optics that tend to produce soft, low-contrast images. These inexpensive “package” lenses may perform OK in cameras with non-interchangeable optics, such as the Panasonic AG-HVX200 or Sony PMW-EX1 — and even in some cameras with interchangeable lenses such as the Panasonic HPX500 with chromatic aberration compensation — but most HD shooters still face the challenge of producing consistently sharp images with good contrast. A polarizer can help this effort considerably.
Effective sky control can help reduce the risk of clipping in bright daylight scenes. A soft-edge ND grad filter should be a part of every HD shooter’s basic kit.
Graduation day
The savvy digital shooter understands that clipping of bright highlights is a serious occupational hazard. Such loss of detail is manifested in ugly blown-out areas of the frame, and it is often associated with amateur images.
Appropriate sky control is, therefore, essential to maintaining detail in areas of the frame that would otherwise appear clipped or blown out. Graduated filters are designed to ameliorate this condition. They are available with a soft, hard, or attenuated transition; I suggest experimenting with the soft-edge variety first — by far the most useful — then moving on from there.
The Formatt Filters HD Soft filter is optimized for use with current-generation high-definition cameras and imagers.
For most shooters, the ND 6/ND 9 soft grads are integral to a core filter complement: The soft edge works well at wide angle for landscapes, leaving the bottom of the frame clear and unaffected. At telephoto (i.e., at higher lens magnification), the hard-edge grad provides better definition along the dividing line. The attenuator-style grad features an even gradient across the entire filter, which is mostly used for special applications. For HD-documentary shooters, a sky-control filter can provide significant benefit when shooting exteriors, with or without a polarizer mounted ahead of it.
A study in contrasts
While the polarizer tends to increase contrast, and thus perceived image sharpness and resolution, a low-contrast filter can also help achieve a more professional-looking image in some cases by increasing the level of detail apparent in the very deep shadows. Contrast control is critical to all shooters, but it is especially crucial to those of us wrangling with popular HD prosumer models — with their tiny imagers, extremely fine pixels, and limited dynamic range.
The soft dimpled pattern is seen here in the Formatt Filters HD Soft #3. You may opt for a lighter grade for most applications.
For several years, I've been recommending the Black Diffusion/FX or Gold Diffusion/FX from Tiffen as the optimal filter types for small-format video. These filters contain an etched pattern that provides a slight diffusion and lowering of contrast without loss of definition. The drawback has been the risk of their embedded image patterns appearing on screen, especially at wide angle and/or when shooting at smaller f-stops.
Owing to its increased resolution, HD has exacerbated this problem, leading some shooters to opt for a diffusion filter type without a visible pattern. Unfortunately, this approach may also produce some resolution loss. One of my favorite filters, the Schneider Optics Digicon, offers a subtle diffused look with only a minimal loss of sharpness in the 1/8 or 1/4 grades.
Another option rapidly gaining traction among high-end shooters is a new generation of HD Soft filters from Formatt Filters, which uses reduced-size, softly defined dimples to achieve the desired diffusion and lowered contrast without definition loss. The modified pattern is designed to minimize its potential visibility onscreen while also interacting favorably with an HD camera's tiny pixel array — the neatly arranged horizontal-and-vertical grid of such imagers potentially wreak havoc with the patterns in some filter types intended originally for standard-definition applications.
Owing to a constrained dynamic range, small-format HD models such as the Panasonic AG-HVX200 may benefit from a low-contrast filter when capturing challenging exteriors. In general, a shooter’s diffusion goals can be achieved via the camera’s Master Detail menu.
Diffusion-by-menu option
Beyond the more favorable contrast afforded by the Formatt Filters HD Soft, Tiffen Soft/FX, and Schneider Optics Digicon, most shooters' diffusion goals can be achieved via the Master Detail menu in their camera setup. This menu can effect virtually the same softening as a physical glass filter, except with greater incremental control. Clearly, there is some economy in this approach as well, because it lets shooters reduce their investment in unnecessary filters.
When applying the menu-setting approach to image control, shooters should bear in mind that excessive correction in-camera may result in a concomitant increase in noise. An optical filter generally poses less risk in this regard, a key point when considering a physical filter over in-camera or more software-oriented approaches.
In general, scene-to-scene color correction can be more effectively applied in post, so supplemental color-correction optical filters are no longer required. Still, the HD shooter should aim to achieve as close as possible to the desired look via lighting and normal white balancing, with the final tweaking achievable relatively easily post-camera.
