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Frequently asked questions about lens filters

Lens filters let you apply some effects to your photos and video from the source, which is right in front of your camera's lens. When you need something to enhance how you capture images, a good lens filter could step up.

What is a lens filter?

Lens filters are not unlike sunglasses or tinted windows in that they serve the purpose of reducing light intensity and protecting your eyes from direct sunlight and UV rays. When you screw or slot in a filter, it is diffusing or skewing any light passing through the lens. Doing so reduces reflections and may help in other respects, like increasing contrast or making an image look cooler or warmer in colour temperature.

Most filters are transparent glass, whereas others may appear more translucent or even opaque if viewed from a distance. They come in the same sizes lenses do. For instance, when you see a 67mm lens filter, it will fit on any lens measuring 67mm in diameter. Manufacturers make their lenses in standardized sizes common in the digital imaging industry, so you aren’t likely to have any problems when looking for a compatible filter.

What types of lens filters are there?

There are several different types of filters, and naming conventions could make it confusing to know what’s what. A UV filter mostly acts to protect the lens’ own glass from scratches or blemishes. They don’t make a big impact on light intensity, unless it’s a specialized UV filter that delivers minor adjustments to colour or highlights.

A polarizing filter darkens the scene to the point of increasing contrast between the lightest and darkest subjects in the frame. It also vastly reduces reflections, which is why it’s a favourite among photographers trying to shoot through glass subjects. You may find there are both circular and linear polarizers, both of which are the same excep that the circular type eliminates reflections in ways the linear ones don’t.

Neutral density filters also come in different types. Some for high contrast situations, others for motion blur or special shooting scenarios. You may also come across soft focus filters ideal for photographing people and children, and still others for black and white photography. Most filters may not do so well in low-light and night conditions, but that largely depends on how much light the filter allows to peek through.

How do lens filters affect image quality?

Lens filters are generally granular in that you can twist them to adjust the intensity of the effect they provide. For instance, if a polarizing filter is too dark, try dialing it back and see what kind of difference it makes. They may require some experimentation to learn how much they change an image when conditions change.

It’s also a best practice to learn about the “filter factor” because filters do require you to adjust camera settings, like aperture, shutter speed and ISO. Filters may give you a factor, like 2X, which means that you multiply your exposure by the same amount, like opening up the lens by one f/stop. One rule of thumb photographers use is to divide the ISO you’ve already set by the filter factor to determine exactly the number to go with when applying that filter.