Lens Filters

So, you’ve gotten the basics of photography down, and now you’re ready to experiment.  You keep hearing people talk about these things called “filters.”  But what are lens filters, exactly, and what do they do?  Keep reading to find out more about a few of the most popular photographic filters.

What are photographic lens filters?

Lens filters--or just, filters--are small pieces of glass or resin plastic that attach to your camera lens.  They are designed to affect your image.  For example, they may be used to retain color saturation, increase or decrease contrast, or allow you to use a slower shutter speed.  Keep in mind that certain filters effectively reduce the amount of light entering your lens--which means you will need to use longer exposures with these filters.  (Sometimes, this is precisely what you want!)  In this article, we will focus on four of the most popular filters: polarizers, UV filters, neutral density and graduated neutral density filters.

A Few Common Filters

Circular Polarizer (CPL)

  • Commonly Used For:  Landscape photography
  • How It Works:  Polarizers reduce the amount of reflected light that enters your lens.  They are a light gray in color and do not affect the color cast of your image.  Polarizers are most effective in the middle of the day, when the sun is harsh and directly overhead.  At this time of day, you may shoot in any direction.  However, at other times of day, you should keep the sun at right angles to your lens.  Otherwise, the polarizing effect will look uneven.  Usually, polarizers are circular, and you are able to rotate them to increase or decrease the effect of the polarizer.  Note that the polarizer will slightly reduce the amount of light entering your lens, so a slightly longer exposure than usual may be necessary.
  • Effects: 
    • Blue skies look bluer.  This may be the most common use of the polarizer.  When the sun is very harsh, blue skies may look washed out in your image.  Using a polarizer will help prevent this from happening.
    • Reflections on surfaces like water and glass are reduced.  Consider the following scenario.  You’d like to photograph a landscape that includes a lake.  In the foreground, you notice some interesting rocks and debris beneath the surface of the water.  A polarizer will allow you to reduce any reflection on the surface of the water in order to capture the objects below the surface of the water.
    • Colors remain more saturated, as the amount of light reflected back off of surfaces such as foliage and rocks is reduced.  This preserves the saturation in the color of the reflective surface.

Neutral Density (ND) Filter

  • Commonly Used For:  Landscape photography; increasing exposure time even in bright light.
  • How It Works:  A neutral density filter is like throwing a pair of sunglasses on your camera.  Like polarizers, ND filters are gray in color, do not affect the color cast in your image, and reduce the amount of light entering your camera.  However, ND filters filter out light uniformly.  They are available in different densities, or strengths.  The strength of the filter is measured in stops of light, since they will reduce the amount of light entering your camera by full stops.  Bonus tip: You can usually use a polarizer as a substitute for a weaker ND filter.
  • Effects:
    • Increase the length of your exposure. This can allow you to capture motion blur, even in bright conditions, by using a slower shutter speed.
    • Increase the maximum aperture, even in bright conditions.  This can allow you to capture a very shallow depth of field, even on a sunny day.

Graduated Neutral Density Filters

  • Commonly Used For:  Landscape photography; photographing in high-contrast situations, especially sunsets/sunrises
  • How It Works:  Graduated ND filters work in the same way as regular (or straight) ND filters, except that the density of the filter varies from one edge to the other.  In other words, one end of the filter may be a deep gray, while the other end is clear glass.  They come in hard or soft (feathered) edge varieties.  A hard edge graduated ND is useful when there is a distinct horizon line in your image (e.g., a seascape, where the sky meets the ocean directly).  A soft or feathered edge is useful when there is a less distinct horizon line (e.g., a city skyline, a mountain range, trees on the horizon, etc.).  Be sure to line up the horizon line with the transitional edge of your graduated ND filter.
  • Effects:
    • Balance the exposure from the brightest area of the scene to the darkest.  The common use is to balance the exposure during a sunset or a sunrise, when the sky is brightly lit, but the foreground remains in shadow.  The clear edge of your filter should align with the shadows in the foreground, while the gray edge should blot out the intense light in the sky--thus creating a balanced exposure.  The effect is similar to the HDR effect that can be created by combining several different exposures on your computer.  But why go through all that computer editing when you can do it all in one shot in-camera?

Ultraviolet (UV) Filters

  • Commonly Used For:  Any photographic style; protection for your lens
  • How It Works:  These filters block out ultraviolet rays of light.  UV filters are clear and do not affect the color of your image.  In the digital era, UV filters are mainly used as a layer of protection against physical damage to your lens.  In the past, UV filters were more critical to preserving the color of photographers’ film, which could be damaged by UV rays.
  • Effects:
    • Protect your lens from physical damage.  Both filters are used as damage control.  If you photograph action sports, or take your camera out on physically-demanding adventures, it’s a great idea to use a UV filter, just in case your lens is involved in some type of physical collision.  These filters are also useful to help seal out dirt, sand, and water from your actual lens, thus reducing the risk of scratches and blemishes.  Think about it as insurance.  What would you rather replace-a $10 filter, or a $300 lens?

Filter Shapes & Sizes

Usually, filters are round and share the same diameter of your lens.  Keep this in mind while shopping for filters--you must buy a filter that is the same size as the lens you plan to pair with it!  An easy way to find out the diameter of your lens is to check your lens cap.  On the side of the cap that faces your lens, you should find a number, like “57mm.”  This is the diameter of your lens (and therefore your lens cap), so you will have to shop for filters that are also 57mm in diameter.

Sometimes, filters also come as square or rectangular sheets.  To use these types of filters, you will need to purchase a special adapter that screws onto your lens and has a slot into which you will slide the rectangular filter.  The benefit of sheet filters is that they are easy to “stack.”  For example, you could combine two ND filters by sliding them both into the adapter together.  This would give you a more pronounced ND effect.

Now that we’ve filtered through the facts, you should feel better equipped to add some new equipment to your camera bag!

If you live in NYC and are interested in landscape photography, make sure to check out this and other photography classes offered at our PhotoUno.


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