Camera Filters Explained Part 2

In Part I of my camera filters explained series, several filter categories were presented—light-balancing, color-compensating, color conversion, and contrast filters. This article will discuss several specialized filters that are used in landscape photography. The next and final article in the series will explore filter systems.

filters-explained

The most common filter in landscape photography is the Polarizer. Its job is to eliminate glare and reflection from water and window surfaces, while saturating color and increasing contrast. How does it work?

Natural, unpolarized light rays vibrate in waves on many different planes. Some rays vibrate up-and-down, some from side-to-side, and others at any angle in-between. Light that strikes particles of moisture in the sky, or bounces off non-metallic surfaces, vibrates in the same plane and is called polarized light. If the light entering the lens is natural, it becomes polarized after passing through the filter.

If the light has been polarized previously, the filter will either lock out the light or let most of it pass through. Since the polarizer filter rotates on your camera’s lens, you decide which light passes through the filter into the lens.

The filter acts like a grill. Light waves that are not aligned with the grill are blocked. Waves that are aligned with the grill pass through. The polarizer is most commonly used to darken a blue sky in landscape photography. You can see the effect of a polarizer as you rotate it and look through the viewfinder.

(Note: More specifically, only light rays hitting a non-metallic surface at an angle of about thirty-five degrees are strongly polarized. Light reaching the surface at other angles is only partially polarized. As much as we may desire, no filter is totally efficient at blocking polarized light.)

No Polarizer
With Polarizer

 

 

 

 

 

 

 

 

 

As previously mentioned, a polarizer is excellent for increasing the contrast between white clouds and a blue sky. Also, by standing at an angle to a window, you can shoot through the glass without creating reflections by adjusting your polarizer.

If you’re shooting in harsh direct light, the polarizer can remove most of the glare and save your image. The image on the left was taken without the polarizer. The image below it had a polarizer attached to the lens. You can see the impact filtering had on the blue sky–but also notice the mountain. It appears much sharper in the polarized image because glare is removed from the image.

However, several factors can cause problems for you when you’re using a polarizer. The main one is the angle of the sun in relation to the direction you’re shooting. Let’s say you want to shoot due north.

The polarizer works to maximum efficiency when the sun is at a right angle to the direction you’re shooting. So, if the sun were in the east or west, you’d get the maximum effect. On the other hand, if the sun is in the north or south, the influence of the filter becomes insignificant. At any angle between ten and ninety degrees there will be impact that will increase as you approach ninety degrees.

Another factor to consider is that the polarizer will absorb about 1.5 to 2 stops of light. If you’re using a hand-held exposure meter, you must compensate for this loss of light. If your camera’s exposure system meters through the lens (TTL), then the camera will make the adjustment for you automatically.

If you handhold your camera, a loss of two stops of light could impact camera shake if it’s subtracted from the shutter speed.

If you use a wide-angle lens, be very careful using a polarizer. First of all, with an extremely wide-angle lens, the filter thickness may cause vignetting.

Special thin polarizers are made by several companies to allow for wide-angle lenses. More important, however, is that the angle of polarization (based on the location of the sun) may not be as great as the angle of your lens. This results in part of the sky being a beautiful dark blue while the rest of the sky remains light blue.

This is more of a problem with a landscape image format than with a portrait format. You’ll be able to detect a difference in the sky tonality. However, the dark blue sky often catches so much attention that we don’t look at the whole sky.

Finally, the sky is uniformly dark blue at high elevations. Depending upon the altitude and angle of the sun, you can turn the sky black in your image. While this is okay for a few shots, it gets boring pretty quickly. With maximum polarization, this effect can take place at an elevation as low as three thousand feet. It usually occurs above six thousand feet, and above eight thousand feet, you must be very aware of it.

polarizer-filter

Linear and Circular Polarizer Filters

There are two types of polarizer filters: linear and circular. By circular, I don’t necessarily mean round. Circular polarizers are made in a variety of shapes–round, rectangular and square–depending on the manufacturer (more about that in Part 3).

Linear polarizers are designed for cameras that are NOT auto focus, or that don’t have a beam splitter. In simple terms, if you have a manual exposure camera, you probably need a linear polarizer. (Note: There are a few exceptions, such as the Olympus OM-1. It’s best to check your manual if you’re not sure.)

In auto focus camera systems, most of the light passing through the lens is reflected up to the viewfinder. However, a small portion passes through the mirror and is reflected down to the auto focus (AF) system. The light passing through the lens is polarized.

When it strikes the mirror reflecting it to the AF system, it becomes scrambled again. In simple terms, the light is not in a useable quality for the AF system. If you use a linear polarizer on an AF camera, you’ll have difficulty establishing focus in any but extremely bright light.

Stated simply, the circular polarizer has a second layer that re-scrambles the light into a circular pattern so that it becomes polarized again when it strikes the AF reflecting mirror. In other words, the light achieves a quality that the AF system can use. A circular polarizer can be used with a manual camera, but since a circular polarizer is more expensive than a linear model, why bother?

Specialty Polarizers

Certain specially made polarizers provide unique opportunities for photographers. One is called a double polarizer (aka polarizer fader), and it features two polarizers on the same filter that rotate independently.

Therefore, you can easily vary the amount of light coming through the lens from normal ND to almost complete opaqueness. This ability is valuable when there is a strong light source, or when you don’t want to carry multiple ND filters in the field. (Note: Be VERY careful of vignetting with wide-angle lenses.)

Hoya and Cokin make variable color polarizers in a variety of color combinations. A yellow/blue combination, for example, will change from yellow to blue as you rotate the filter. If you want to change the intensity of the amount of yellow (or blue), just rotate the filter until you get the desired effect.

Several filter companies produce special polarizers that combine a polarizer with another type of filter. By using one filter instead of two, you reduce the chance of vignetting while using a wide-angle lens. The most popular combination is to add a warming filter (either 81A or a Tiffen 812) to the polarizer.

Hoya and Singh-Ray produce a UV-Polarizer combination that removes haze by eliminating ultraviolet rays while it polarizes the light. Singh-Ray also produces an Intensifier-Polarizer combination.

Enhancers or intensifiers (the name depending upon the manufacturer) are unique filters that can greatly assist the landscape photographer. They enhance, or intensify, certain colors in the scene while having little effect on the other colors. There are four basic types that are available:

No Filter
Enhancer

 

The red intensifier (sometimes simply called an intensifier) is used to enhance red, orange, and rust-brown subjects to lend more color saturation and contrast. It’s sometimes also called the “didymium” filter because of the special glass used in its construction.

The picture on the left was taken in central Oregon without any filters. The picture to the right was taken with a red intensifier. If you look at the filtered picture long enough, the “normal” picture will appear more greenish than it actually is.

The intensifier filter is often used to produce great autumn scenes. It adds punch because it enhances the central fall colors. However, any scene with red, orange, and/or brown subjects (such as a bowl of red apples) will benefit from one of these filters. Sometimes architectural photographers use an intensifier to emphasize certain building features or interiors.

A green intensifier enhances the green portion of the spectrum without impacting the other colors. It’s very helpful when you’re working with flowers, landscapes, and grass. Imagine nice yellow flowers with dull green leaves. You can provide more intense green to the leaves with a green intensifier.

Blue intensifiers work solely on the blue part of the color spectrum, so they work well with seascapes or cloudy skies. Remember; the polarizer is affected by the sun’s direction. When a polarizer doesn’t provide enough saturation, a blue intensifier will save the shot. For really great contrast in the sky and clouds, you can combine a polarizer and a blue enhancer. (Note: A word of warning in using this filter:

Part 1 of this series mentioned that light in heavy shade takes on a bluish tone due to its color temperature. Imagine a white house where the front of the house is in shade due to backlighting. If you use a blue enhancer to bring out the blue sky, it will also bring out the blue that your eye does not see in the shaded portion of the house!)

Sing-Ray makes a color intensifier that enhances both cool AND warm colors without affecting neutral tones. It allows increased color saturation over the full color spectrum. This intensifier can be purchased separately or combined with the polarizer as mentioned above.

Neutral density (ND) filters reduce the amount of light reaching the film. Because many photographers can’t fathom a reason for intentionally reducing light, these filters are often ignored. However, they offer some interesting possibilities for images that might otherwise escape. These filters have three general uses: 

Twenty second exposure

To enable a slow shutter speed.
Whether you’re using a fast film or the day is simply bright, you might not be able to get a low enough shutter speed to shoot a stream and capture that soft effect of flowing water. Use a neutral density filter, or combination of them, and your problem is solved.

The photo above was taken in mid-afternoon along the Oregon Coast. My intention was to have the waves overlapping–a shot not visible to the naked eye. However, the bright sunshine wouldn’t give me a shutter speed low enough for that effect.

By combining a couple of ND filters, I was able to take this twenty-five second exposure.Whenever you want to record slow movement of any subject–such as cars, clouds, waterfalls, streams, etc.–the ND filter is your best friend.

If you obtain a 9-stop ND filter, you can achieve slow enough shutter speeds in daylight so that moving objects won’t be recorded, but anything that is stationary will appear on the image.

Since a ND filter reduces the light to less than 1/500th of its original intensity, it can also be used to safely photograph solar eclipses and other very bright light sources.

To decrease depth of field and allow wider apertures to be used. This will allow the photographer to separate the subject from the background and give the subject more impact.

To decrease the effective ISO of higher speed films.
If you reach into your camera bag on a bright, sunny day and find only high-speed film, you may be in trouble.

You’ll end up needing a very fast shutter speed–maybe one that’s faster than your camera can provide! The ND filter will enable you to use high-speed films in those situations.

Types of Neutral Density Filters

There are three types of ND filters. In the first, the neutral density effect covers the entire filter. This type of ND filter was used in all of the previous examples.

In the second type, the neutral density effect covers only half of the filter.

It’s called a “Graduated” ND filter. Imagine a scene in which the foreground is six stops darker than the sky. This is a shot that your film normally can’t handle because the tonal range is too great. Use a graduated ND filter with the ND part absorbing three stops of light.

Place the ND part over the sky. Now there are only three stops of light difference between the foreground and sky. Your film can handle that range. (I’ll discuss the pros and cons of rectangular and round graduated ND filters in Part 3 of this series.)

In the third type of ND filter–the “Center” ND filter–the ND effect works in the center and is clear on the edges. There’s usually about a stop difference between the center and the edge. This filter gives the impression of a gradual fade from the center to the edge.

It helps in cases where vignetting can’t be avoided. It’s also excellent in situations where the central portion of the scene is the brightest, and the edges are darker.

A word of warning about ND filters: The filters should be totally neutral in color. They should not add any tint to the scene. Several years ago, Joe Englander did an excellent article demonstrating that all ND filters are not neutral.

When considering purchasing a ND filter, compare several manufacturers by bringing a white sheet of paper to the store. Place the filters side-by-side on the paper to determine which ones are true ND filters and which have a slight tint.

Contrast controlling filters can save quite a few landscape shots. Controlling contrast is very difficult in situations with bright sun and deep shadows. Look at the photo on the extreme left. Expose for the bright portion and the shadows go black. Expose for the shadows and you’ll wash out the bright area. We’ve all faced situations like this.

No Filter
Ultra Contrast 3

Tiffen produces a series of filters called “Ultra Contrast” that lower contrast evenly throughout the image.

They work with the surrounding ambient light to spread it evenly across the whole image without any flare. The photo on the right was shot with an ultra contrast filter. Although contrast is reduced, the details in both the dark and light areas are useable.

Soft Focus

The ultra contrast filter comes in various strengths from one to five, which allows you to choose the right one for a given situation. Most people start out with #3 if they’re going to purchase only one filter. If they purchase two, they usually choose #2 and #4.

Soft Focus filters are sometimes called diffusers. In a previous Apogee article, I explained how to use multiple exposures to achieve a soft focus effect that can also be created by using Vaseline on an old filter or by stretching high quality nylon across the lens.

However, to achieve consistent results every time, a filter is essential. Soft focus does not mean out-of-focus. The image has a clear focus and a soft gradation. This is accomplished by scattering the light (through a variety of methods) across the filter. Virtually all filter manufacturers produce soft focus filters. They are used very commonly in portraiture work to remove harsh edges and de-emphasize facial blemishes.

Many photographers are now using soft focus filters for landscape images to enhance the creative aspect of the scene. My favorite soft focus filter is Tiffen’s “Black Pro Mist.” It’s subtler than most soft focus filters, yet it provides a misty glow to the scene that I find attractive.

Most soft focus filters are produced in a variety of strengths to permit the photographer to determine the desired effect. The image on the left was shot with a soft focus filter. (Unfortunately, I didn’t record which type of filter I used.)

If I discussed all the other special effect filters on the market, this article would triple in length. I tried to discuss some of the more valuable special effect filters, but value depends on the scene that you are photographing.

Some of the other special filters include fog, star, multi-image (the same image is reproduce several times on the frame), sepia, infrared, center spot (the center is clear while the rest of the filter has some effect such as soft focus or a distinct color), split-field (the bottom portion of the filter is a close-up lens, the top has no glass, allowing great depth of field in a shot), and dual image (for double exposures).

By Jim Altengarten,

All written content (and most images) in these articles are copyrighted by the authors. Copyrighted material from Apogee Photo Mag should not be used elsewhere without seeking the authors permission.

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