Wednesday, July 1, 2009

Filters and Photography

Filters can add special effects or abilities to your camera lens. Understanding how filters work will give you an extra arsenal of equipment to create that magical shot you’ve been looking for.

Most lenses have the ability to add filters, primarily by screwing them on in front of the lens while some lenses require the filters to be attached at the rear end of the lens. Filters are used for several different reasons: increasing contrast, changing the exposure, capturing invisible light or minimizing reflections are just a few to name.

The use of filters has gone downhill in this age of digital photography. These days it’s simply easier to make these changes in post-production instead of using a filter during the photo shoot.

While that might be true, there are still some things we can’t change in post-production, and filters can become a necessity.

UV Filters

UV stands for Ultraviolet, which is light that is invisible to the human eye. UV filters were used to cut down on haziness, such as in mountains and around coastal areas, but the digital sensor isn’t as sensitive to this as 35mm film was. However the UV filters are still around, mainly because these filters are used for lens protection.

Having a UV filter attached to the lens at all times makes the lens more protected from scratches, dust, weather and accidentally dropping the lens. There are debates among photographers about the use of UV filters; some argue that they visually affect the outcome of the photograph while others argue that they don’t affect it and that the filter is a great insurance.

I personally always have a UV filter screwed onto every single one of my lenses, and I’ve had one of my lenses saved thanks to the attached filter. However, if you are going to use a UV filter, don’t buy the cheapest one you can find. If you have a good lens, buy something like a high-end B+W filter.
ND Filters

ND filters, or Neutral Density filters, are a great way to take control over exposure time. These filters are used to reduce the amount of light that reaches the sensor, which makes it possible for the photographer to use a larger aperture for a longer period of time then what would be normal under given circumstances.

An example of this would be the ability to photograph a waterfall with a slow shutter speed during a bright day. Without a ND filter most lenses would not be able to use an aperture small enough for long exposures but with an ND filter attached the photographer can mix and match just how he wants it.

Graduated ND Filters

These filters have the same principle as the regular ND filters but with one important distinction, they do not have the ND effect on the whole glass. The ND effect is gradual and is perfect if you want to have the sky darkened but not the foreground for example. These filters have their limits, such as the gradual transition is a straight line, which might not always be the case with nature… oh, and they are also rather expensive. Most of these filters are rectangular and uses a special holder to place them in.

Polarizing Filters

These polarizing filters have many uses, and are one of my favorite filters to use. Most of them are circular, often called Pol-Cir or CPL filters, and you change the level of polarization by rotating the outer layer of the filter. The polarizer filter affects the photographs in such a way that cannot be reproduced in post-production, which makes it a very useful tool even today.

What it does is reduces reflections on non-metallic surfaces, such as water and glass. Removing reflections can be very useful in both urban and wild life situations and have the ability to totally alter the outcome of the photograph.

Another effect the polarizing filter has is that it increases contrast and color saturation while at the same time reducing haze. This effect can clearly be seen in skies, in which the sky can be darkened and more colorful but keeping the clouds white.

A quick word of advice though is that a polarizing filter will, depending on brand and quality, not let 100% light through — which will affect the exposure. With most brands you will loose one full-stop.

Macro Filters

Macro filters, close-up filters or diopters, are not ordinary filters — they are more like an extra lens you place in front of another lens. This makes close-ups possible even with normal or telephoto lenses, although the result is often not true 1:1 macro. Several filters can be stacked on top of each other to intensify the effect.

I personally would recommend people look into getting an extension tube instead. Extension tubes change the closest possible focus length, without affecting the image quality as badly as macro filters do. The best option is obviously a true macro lens, but an extension tube is much cheaper and might be a good first step into the world of macro photography, and the extension tube can be used together with a macro lens to enhance the magnification.

Macro filters have many drawbacks such as softening up the image considerably, and these filters often produce lacking quality. Use with caution.

Color Filters

Color filters are rarely used anymore; they were primarily used for black & white photography to manipulate the contrast. An example is using a yellow, orange or red filter, which will increase the contrast between skies and clouds, making the clouds really stand out. These days the effects can quite easily be reproduced digitally with the help of levels and channels.

IR Filters

IR stands for Infrared, and these wavelengths are on the opposite side of the light spectrum from UV. To photograph in IR you need a filter that only lets through IR light, however there are some problems with modern cameras. The sensor is constructed to not record IR light, and unless you want to permanently modify your camera (or purchase specially designed cameras such as Canon’s 20Da) there are some restrictions. This technique is so unique and odd that I will dedicate an entire article about IR photography later on instead of writing how it all works in this one.

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