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If you are old enough to have used a film camera, you know why people needed lens filters in order to accomplish visual effects in their images. Back in the film days, you had limited control over white balance or ISO. Once you selected your film from the available film stock, and put it in your camera, you were stuck with a roll (24 or 36 exposures) of single ISO negative or slide film that was probably daylight balanced. In order to not waste money, you did everything you could to carefully mete out your images and make the most of them.
To help you make great images in the film days, you needed certain filters to help fix your white balance, and neutral density (ND) filters to allow you to slow your shutter speeds down. That was then, this is now. With the advent of digital cameras and the high-powered abilities of most image editing software, you can accomplish digitally much of the work that filters used to do. Is there still a place in modern digital photography for optical lens filters?
The answer is yes, but only for a few specific types of filters. In fact, you may find it difficult to get many filters in your local camera store that would have been readily available in the film camera days. Most bricks and mortar camera stores carry few filters. The more unusual filters might be found in the bargain bin section, next to the books on how to use your new Canon 5D mark 1 (hint: that is an old digital camera).
I find that optical lens filters break down into six general types: UV/skylight filters, color modifiers, special effects, specialty filters, ND filters (including graduated), and circular polarizers. Most optical filters can be replaced by digital processes, either in the camera itself or in post-production. Some optical filters are really big and all take up space in your bag.
Let’s consider UV or skylight filters. Film stock was often sensitive to UV light so it was important to protect your film by using a filter so that UV light wouldn’t make the images hazy. Modern digital cameras are not susceptible to UV light interfering with their sensors as there are already UV and IR filters built into the cameras (we will discuss the importance of this later). Today, UV or skylight filters serve a completely different purpose: many photographers use them to protect the front element of their lenses.
As an aside, there are two schools of thought regarding UV or skylight filters. Some argue that putting a cheap filter in front of a really expensive lens significantly degrades the optical properties of your lens and that most good quality lenses have great coatings and are quite robust. Alternatively, others would prefer to replace a $100 filter than replace a $2000 lens. While I agree you should never use cheap filters, I do tend to think that if you use good filters they do protect your investment in much more expensive lenses. I have replaced lots of filters that were shattered from an impact. In all of those cases, the front lens elements were protected from contact by the filter. I am not sure that would have occurred without the sacrificial filters.
Regardless, since these UV/skylight filters don’t cause any significant changes to your image, they really are only useful for physical lens protection.
Color filters were another common filter used with film cameras for simple color correction. Back in the film days, the film stock was mostly daylight balanced so if your images were taken in non-daylight conditions, you would need to use a color filter to correct your white balance. Although film processors had some ability to adjust the white balance in the lab, back then – today too, for that matter – it was always easier when you got things right in camera. Color filters are still available but are more of a novelty item, used for a specific effect, often in concert with gelled flashes and strobes. They are also still used for film cameras, instant cameras, and for specific applications like underwater photography.
Once upon a time, there were lots of special effects filters that would produce in-camera special effects like grids, streaks, and starbursts. These all still work on digital cameras, however, most of these effects can be digitally produced, reducing the need for the optical filter. Many film shooters will take their images and then scan them to edit them, so the extra effort and cost of using special effects filters seem unnecessary. They are also difficult to find.
The next filter type to consider is the neutral density filters, commonly used by landscape photographers (both film and digital). These divide into two groups: graduated neutral density filters and overall neutral density filters. Acting like sunglasses for your camera, graduated neutral density filters are all neutral colored – they should impart little color change – and darken only part of the image. Graduated filters help deal with the dynamic range of your sensors, particularly when shooting into scenes that are very bright and very dark in the same view. Most modern digital cameras have a dynamic range of about 10 – 14 stops whereas your eyes are more like 20 stops. Keep in mind that this is not really a fair comparison because our eyes work quite differently from camera sensors. Graduated neutral density filters can usually be applied in post-processing. Although, if the dynamic range is really huge, it often means you can take one image rather than multiple images that need to be composited (this is what HDR images really are).
A neutral density filter (non-graduated) is the first optical filter type that does things that cannot be easily duplicated, either in camera or in post-production. At least not all of its functions. While it is certainly possible to darken your images digitally in post, a non-graduated neutral density filter allows you to take images that your camera would not allow you to take in full sunlight. In full sun, it may be so bright that you may not be able to stop your lens down and slow your shutter down sufficiently to get motion to blur. Non-graduated neutral density filters allow you to slow your shutter speed down in the field when conditions are bright. You will be able to take images of moving subjects in bright locales and blur the motion to create interesting effects. For example, waterfalls are often shot using a non-graduated neutral density filter. Neutral density filters are often measured in stops to indicate the number of stops you can slow things down. At the extreme end of the non-graduated neutral density filters are the specialty filters used for photographing solar eclipses. Without these strong filters, the sun can permanently damage camera sensors.
The second optical filter type that cannot be duplicated in post-processing or in-camera are specialty filters related to UV and IR light. By default, cameras have filters on their sensors that cut UV and IR light out so that only visible light is recorded. However, it is possible to get these filters removed (you have to send your camera body away) to allow you to shoot UV-only, full spectrum (which includes UV, visible and IR), or IR-only images. Once this is done, your modified camera is generally limited to that particular use, but the images it produces can be quite interesting. By using specialty filters on a modified camera body that allows for full spectrum, you can control what portion of the spectrum is visible in your images. There are cut filters that allow full spectrum sensors to only see UV, visible light or IR spectrum. These filters cannot be duplicated in post-processing.
The final optical filter type that cannot be duplicated in post-processing is a circular polarizer. There are actually two types of polarizers, linear and circular. They both cut the same light out but circular polarizers can rotate an allow you to find the optimal orientation whereas linear polarizers are fixed (you should only use circular polarizers unless you know what you are doing). Circular polarizers do two things: cut down reflections and increase contrast. Some also act as a weak neutral density filter. When light hits a metallic or watery surface, the reflected light tends to be polarized (all the light is vibrating in the same direction). The circular polarizer lets you filter out this polarized light. You do this by turning the filter. The change can be quite dramatic, and it cannot be achieved in any practical sense through post-processing. In addition, because there is always some polarized light in the atmosphere, the filter will make the colors in your images punchier. This is a secondary feature of polarizers but adds to their use. Colors just pop more. Different brands and types alter how much this occurs. In general, you can’t go wrong using a circular polarizer, particularly for landscape photography.
Many filters that were used with film cameras are not really required anymore because of the ability to control white balance and ISO. Other filters created effects that can easily be duplicated using image editing software like Photoshop. Despite this there are a few filter types that cannot be replaced by processes applied in post, thus they remain vital tools in your photographer’s toolbox.
Do you use filters? Share with us in the comments below.