B&H Photo - Introduction to filters
 

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Introduction to Filters

 

There are many filter systems and as many individual filters to choose from as there are leaves in the forest. The options are vast and varied and to the uninitiated, selecting a filter system can be a daunting undertaking. Sometimes the choice is dictated by which camera you use or which lens you own. Some of the different varieties of filters include: Screw-on, Bayonet, Series, Drop-in and Square and rectangular systems and Matte Boxes. Filters may be glass, plastic, resin, or soft polyester gelatin.

Filter'sOther important filter issues are: What effect do I want to achieve? What lens is the filter for? What size filter does my lens take? Which filter system is best for me? What filters do I really need? So, before you invest in a mountain of filters, here is a brief overview of what is available:

 

Screw-on Filters

The most common type of filter is the glass screw-on mount. This is simply a round piece of glass or plastic, mounted inside a threaded metal ring that “screws” on to the front of your lens. There are more options for screw-on filters than any other design.

They are also the easiest kinds of filters to use. No adapters are required – just screw it on and you’re ready to go. Screw-on filters are available in sizes to match a specific lens diameter. When you buy a lens, the instructions (or often on the inside of the lens cap) will state what size filter that particular lens accepts. For example, if you were to purchase a Nikon 50mm f/1.8, lens the filter size would be 52mm.

Consequently, any screw-on filter you buy for that particular lens would have to be 52mm - regardless of which manufacturer of filter you prefer. There are occasions when a larger sized filter may be used, but we will cover that later.

Every imaginable effect for screw-on filters exists. From a simple UV (ultraviolet) filter that provides protection for the glass elements in your lens to making a Caribbean scene more dramatic with a graduated sunrise filter, there is a screw on filter available for every effect. Although there are exceptions, most screw filters are double threaded which means that additional filters can be stacked one on top of the other. This will allow you to do combine the effects of two filters at the same time. An example would be if you were shooting black and white film and using a red filter in conjunction with a polarizer. This resulting dramatic effect would resemble a threatening storm.

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Multi-coating

Multi-coating is an excellent way to protect your images from unwanted flare. However, not all filters come with multi-coating. Some manufacturers produce the same filter both with and without multi-coating and when you want to buy that particular filter, you must specify whether you want multi-coating or not. Unless you specifically request multi-coating you will, most likely, be sold a non-multi-coated filter. In addition, many filters are not even produced with multi-coating as an option. That depends on the manufacturer. And remember, a multi-coated filter will cost you more than a non-multi-coated filter. However, many pros feel the added benefits of multi-coating outweigh the added expense.

What is multi-coating? Frequently, “ghost images” appear in backlit photographs or when light enters at extreme angles from the side. This is caused by a reflection created on the surface that occurs when light enters the filter glass. Normal untreated glass causes light loss of approximately 2-4% due to reflection. Along with light loss, flare can occur which causes the picture to appear flat and washed out. The reason for this is due to the different refractive characteristics of glass and air.

Filter coating is necessary to compensate for this difference and to allow reflection-free light transmission. To achieve this, a scratch-resistant metallic oxide coating is applied to the surface in a high-vacuum process. A single layer coating can reduce reflection by more than half. Further reduction of internal reflections throughout the entire spectral range requires several layers.

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Bayonet Mounts

A bayonet mount implies exactly what it means. Instead of screwing it on, you “twist” it on with a short snap, much like a soldier would attach his bayonet to a rifle. The principle of a bayonet mount lens is the same as a screw-on, i.e.. a piece of glass held inside a ring. However, the physical attachment to the lens is different. Bayonets are not threaded and thus require a firm twist to hold them on. Medium format manufacturers like Hasselblad and Rollei are particularly noted for their bayonet design in filters. There are also various video cameras that make use of bayonet mounts as well. Chances are if you are using a traditional 35mm camera (film or digital), you won’t ever have need for a bayonet mount filter. Bayonet mounts are somewhat limited to a few specific types of filters.

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Drop-ins

Many lens manufacturers design longer telephoto lenses with very wide front diameters, i.e. 300mm, 400mm and 600mm lenses. These lenses are long, large, and heavy and often require tripod mounting for use.

Some of these lenses do, in fact, accept screw-on filters on the front element. However, these large-sized glass filters tend to be very expensive and not affordable by the general photo population. Nor is it cost-effective for manufacturers to produce many different large size filters for a few long lenses. However, in order to give users of these lenses some filter flexibility at a reasonable cost, manufacturers design these longer lenses with what is called a “drop-in” system for filters.

When looking at these longer lenses, you will notice that there is often a small compartment towards the rear of the lens. This compartment is usually held in place with a release screw. Remove the compartment, and you will find a filter holder for small, round, “drop-in” filters (the holder is usually included with the purchase of the lens). Some of these filter holders accept screw-on filter sizes such as 52mm. Please note that more often than not, long lenses require the use of a gel filter holder and use gels that must be cut to size. A potential buyer should always inquire as to what size filter a particular long lens accepts. Manufacturers also make specific drop-in polarizers for longer lenses. It is important to remember that a polarizer for a long Canon lens will NOT fit in a long Nikon lens and vice versa. Such filters tend to be lens specific. Always check with your sales person.

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Square and Rectangular Filter Systems

Square and rectangular filters come in a variety of sizes with the most popular being 3x3”, 4x4” or 4x6”. Larger sizes are available and are very popular with cinematographers. Square, plastic filters are traditionally less expensive than round glass filters. They also weigh less and provide the user with certain special effects that glass filters may not offer. For the pro or high-end amateur photographer, videographer and cinematographer, square/rectangular systems can sometimes offer a higher degree of control over the image than glass filters. There are glass rectangular filters but they are usually pricey and generally only appeal to either the cinema community or large format photography shooters.

Square/Rectangular filters can be made from different materials. The comparatively inexpensive Cokin system is plastic while the Lee pro system can be either high-quality resin or less-expensive polyester. Kodak makes simple polyester gels that are extremely popular and reasonably priced.

Square and rectangular filter systems solve problems that round, screw-on filters often cannot resolve. To begin with, one square or rectangular filter can be used with many different size lenses. As long as you have the appropriate size adapter rings, in most cases, one filter will serve the purpose.

Another benefit is if you are shooting a landscape where the horizon line is off-center and you want to balance the light intensity in both parts of the scene, i.e. bright sky, shaded foreground . Rectangular filters allow the transition to be blended into the scene, often imperceptibly. This is because they can be shifted up and down in the filter holder to fit the scene as desired. Some graduated rectangular filters are available with soft or hard transitions from dark to clear. The soft edge is recommended for wide-angle lenses and the hard edge is recommended for normal and longer lenses.

Whether you purchase a simple, economical system such as Cokin “A”or “P” filters, a higher end pro system like Lee or HiTech, the principle for all are the same. The system will be composed of three parts: an adapter ring for your lens, the filter holder that fits in to adapter ring, and the filter(s).

In addition to the holder and adapter rings, some systems, like Lee and Lindahl, offer compendium hoods that not only serve as lens shades but also provide slots that can hold the filters inside.

These hoods are extremely popular with wedding, fashion, large format and videographers who are very sensitive to the negative effects of flare. Compendiums are also very good when the use of special effects is required (i.e. photo of a bride and groom inside the silhouette of a champagne glass).

If there is any disadvantage to this kind of system, it is that they are slow to use. Between the adapter rings, dealing with filter holders and having to slip the filters in, it can be cumbersome, especially when hand holding. However, as previously stated, this way of shooting offers extensive image control and special effects. Despite the digital explosion, these systems remain very popular with photographers of all genres.

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Gel Filters

Soft polyester gel filters are an inexpensive and effective way to maintain precise color and temperature control over an image. Companies such as Kodak and Optiflex (Lee) make square gel filters in a wide variety of colors and temperatures. The most popular sizes are 3x3” and 4x4”. Kodak alone makes over 100 types of gel (Wratten) filters. They are also available in larger rectangular sizes that are popular with cinematographers. Gels can be thrown in a camera bag, taped over a lens if necessary and are considered somewhat disposable. One convenient aspect of polyester gels is that they can be trimmed should an odd size be required.

Whereas round glass filters are, for the most part, available in standardized color temperatures, certain polyester gels can be bought in smaller increments (neutral density and color compensating, for example). Most photographers prefer to use a gel holder to secure the filter. Gel holders can be comparatively inexpensive depending on brand and style. When in a pinch or on a limited budget, gels can be taped on to the lens.

Companies such as Lee also produce a higher end, resin type rectangular filter. These filters cost more money but last longer, don’t “crinkle” and are easier to use because of their added rigidity.

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Series Filters

Series 9 filters by Tiffen are a unique filter system once popular with older lens and camera design. Requiring a Series 9 adapter ring, this system allows you to use one standard size filter (Series 9) on many lens sizes. Series 9 filters, although screw-on style, require a bit more work to set up. The glass filter drops into the adapter ring and is held securely in place with the included retaining ring (adapter ring sold separately). Series 9 filters have no threads. Although these filters are no longer as popular as they used to be, they allow the use of filters for harder to fit lenses, a common problem with older camera lenses.

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Stepping Rings

What happens when you have two lenses and they are two different filter sizes? There are two choices: First, you can buy individual filters for each lens. This is fine although it can run into a lot of money duplicating filters for each lens. It’s also more to carry around in your bag. Second, and perhaps more practical, is to use a “stepping ring”. In this way, if you have two lenses that are 58mm and 52mm, you can buy all your filters in 58mm and use them on the 52mm lens. How? A 52-58mm “Step Up” ring will solve the problem.

Many people confuse the terms “Step Up” and “Step Down”. It is critical to remember that you are always “stepping” from lens to filter size. Consequently, a 52-58mm step up ring allows you to use a 58mm filter on a 52mm lens size while a 58-52mm step down ring means using a 52mm filter on a 58mm lens size (generally not advisable). When using step down rings it is crucial that you remember that a smaller filter on a larger lens diameter means that the filter might encroach on the image and cause “vignetting”, a cutting off of the edges of the photo that shows up as “black: corners. Sometimes you can get away with it, particularly if a telephoto lens is involved. However, the practice is risky. Always test by looking through the lens and noticing the edges of the image.

Try viewing against a very light background. Think of holding a penny against a silver dollar. The penny is clearly visible inside the larger denomination. Conversely, if you held the silver dollar against the penny, the larger coin completely covers the penny.

Stepping rings are a convenient and inexpensive way to avoid having to buy extra filters. Besides, one stepping ring weighs much less than duplicate filters.

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