Tiffen Camera Filters Effect of Depth of Field and Focal Length Changes, Multiple Filter Use

Effect of Depth of Field and Focal Length Changes

Standard color filters generally function without change through variations in depth of field and focal length. This may not be true of many of the "special effect" filter types. There are no solid rules for predicting the variation in filter effect due to depth-of-field or focal length changes. There are some things we can expect, however. Let's look at a fog/mist type filter that causes a light to glow, or flare. Take the example of a certain grade filter where we can see that the ratio of light diameter to glow diameter is, say, 1:3. As we view this through a changing focal length, we will see that the ratio remains the same, although the magnification will vary accordingly. So the decision to use a filter of a different grade to maintain a certain appearance at different focal lengths will be based on wanting to change the ratio, as opposed to any otherwise corresponding relationship. Tests are advisable for critical applications.

Sizes, Shapes, and Mounting Techniques

Filters are available in round and rectangular shapes in many sizes. Round filters generally come supplied with metal rings that mount directly to the lens. Frugal filter users might find it preferable to use adapters allowing the use of a set of filters of a single size with any lenses of equal or smaller sizes. Round filters also can be supplied with self- rotating mounts, where needed, as for polarizers. They can be readily stacked in combination. Rectangular filters require the use of a special filter holder, or matte box. They offer the additional benefit of allowing slidability, for effects that must be precisely aligned within an image, such as gradated filters. In all cases, it is advisable to use a mounting system that allows for sturdy support and ready manipulation. In addition, the use of a lens shade at the outermost mounting position (from the lens) will minimize the effect of stray off-axis reflections.

Multiple Filter Use

When any single filter is not enough to produce the desired results, use combinations. Choose carefully, to minimize the number required. Usually the job can be done with no more than three filters. Use filters that individually add to the final effect, without cancelling each other out. For

example, don't use a polarizer, which can increase color saturation, in combination with a low contrast filter which reduces saturation, unless it works for some other reason (the polarizer could also be reducing reflections, for instance). Generally, the order they are mounted in is not important.

Secondary Reflections

Lighting can cause flare problems, especially when using more than one filter. Lights in the image pose the greatest difficulties. They can reflect between filter surfaces and cause unwanted secondary reflections. Maintaining parallelism between filters, and

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CAMERA FILTERS © Ira Tiffen