Filters are a lens add-on that are interesting to many photographers. Providing a number of different of effects and options, filters can either protect your lens investments or add value to your quality optics by improving their performance. Today, we're going to take a look at the use of filters.
First of all, let's go over the basics of attaching a filter to your lens. The most important part of choosing a compatible filter is to choose the correct size filter.
Nearly every lens has a front filter thread. This refers to the notches and grooves on the front part of the lens that allow for a filter to screw into it. The tricky part is that the diameter of this filter thread differs from lens to lens. As a result, you can't buy one filter and expect it to fit on each and every lens.
The filter thread is expressed in millimeters, or mm. This "mm" holds no correlation to the "mm" zoom of your lens. Larger looking lenses will require larger filters obviously. The best way to choose the right size filter is to Google your lens and check the front filter thread. The data is readily available on the manufacturer's website. Some, but not all, lenses have the filter size printed on them. It's express my a number in millimeters next to a circle with a slash through it.
As a note, some lenses do not have the ability to attach filters to the front. Nikon's flagship 14-24mm wide angle lens is a good example of this. Companies such as Cokin have manufactured complex filter solutions that sit in front of the lens, and require some additional pieces.
Nikon's 14-24mm lens is a fantastic lens, but can be somewhat limiting in filter usage because of the lack of the front filter thread on the bulbous front element.
Finally, some lenses have special rear filters. I have seen this both in huge telephotos with huge front elements, as well as some wide angle lenses with bulbous front elements. These lenses may feature "drop in" filters that are inserted not on the front of the lens, but somewhere in the middle or near the rear. My Sigma 15-30mm lens, for example, has a rear filter holder.
When choosing a lens, your need for a filter is something to keep in mind. The aforementioned Nikon 14-24mm is frequently talked of as one of the world's best wide angle lenses, but the inability to use filters causes some professionals to seek other, filter-ready options. If you are the type of photographer that really likes filters, make sure you choose lenses that allow for them.
Filters are by no means created equal. The quality of the glass used varies widely from brand to brand.
Choosing cheap filters compromises the optical quality of your expensive camera lenses. Why put a low quality filter on the front of the lens? Poorly constructed filters can nullify the good optics of professional caliber lenses. It is tempting to save some money by choosing that inexpensive filter, but if you already have a lot of money invested in the lens itself, this approach makes little sense.
Checking reviews and doing research is always a must in choosing camera gear and accessories, and filters are by no means an exception. Too many eBay sellers hawk inexpensive lens filters to beginners. Having made the mistake of using some of these filters, I can personally testify that off-brand filters are a waste of time and lens quality.
Types of Filters
In this section, we are going to look at some of the most popular types of filters and the effects on images that they provide.
Neutral Density Filters
The first time I saw a neutral density filter, I could hardly understand their purpose. Neutral density filters, or ND Filters, are designed to decrease the amount of light passing through the lens and thus reduce the amount that reaches the sensor.
What are some practical uses for these filters? I personally use a neutral density filter with flash. Let's take a scenario in using flash that you may have faced before. Let's say that we want to use a flash, but in sunlight for some nice fill flash. We also want to use a large aperture to preserve the nice shallow depth of field.
This Hoya ND filter is an example of a neutral density filter.
If we open the aperture up, even if we have our ISO all the way down, we may be faced with a shutter speed that is above our sync speed - thus the flash will not sync as it is supposed to. What we need to do is reduce the total amount of light reaching the sensor, and an ND filter is a fantastic way of doing this. With these filters on our lenses, we reduce the net amount of light reaching the sensor, keep our aperture wide open and the shutter speed in a syncable range.
We'll talk more about these filters in part two of this series.
Another filter used by landscape photographers frequently is a polarizer. These are a favorite because they can really help to bring out the blues of a sky and improve the contrast and coloring of the photo.
Many people are unclear regarding the difference between circular and linear polarizers. In the simplest terms possible, if you are using a modern autofocus camera, you should choose the circular polarizer for the lens to work properly with autofocus.
In this image from B&W's website, we can see the effects of a polarizing filter. On the right, notice the deeper blue skies and the reduction of reflection on both the glass of the building and water.
The purpose of polarizers is different from an ND filter, but they also reduce the amount of light that passes through. The amount varies from filter to filter, but generally it is around two stops.
Polarizers can also help to cut the amount of reflection from surfaces like water and glass. The classic example for using a polarizer is for a photo of a pond to have better vision of what's below the water's surface.
One thing to keep an eye on is choosing a polarizer for a wide angle lens. The wider the lens, the more likely you are to get vignetting, or darkening of the corners. To avoid this effect, I would highly recommend taking care in purchasing a polarizer that is labeled as "thin" in order to reduce or eliminate the vignetting effect.
Polarizers are great tools for landscape and wildlife photographers. However, make sure not to leave them on all the time, as you may want the the most light possible to reach the sensor. Polarizers are less popular for any type of people photography.
One filter that I rarely leave home without is a protective filter. These filters are so important to protecting your investment in your lenses. Having a dropped lens be saved by a $30 filter on the front, I am forever loyal towards using a protective filter. When you deal with expensive glass, it's foolish to not opt for the additional expense of protecting the lens.
The protective filter on my Canon 35L has saved the glass of the lens itself from many tight spots and has protected my investment in the lens itself.
Furthermore, wedding photography (and many other types as well) is a run and gun type of business. Honestly, I rarely use lens caps because they're too cumbersome and often end up lost anyway. I store my lenses in my bag with the filters attached, but no caps. I can quickly attach the lenses and not worry about removing caps and thus stay in the flow of shooting.
Protective filters are often labeled and sold as just that. Other filters used for protection purposes are "UV" filters, for example. We'll talk more about those in part two of this series.
The filters discussed above are useful tools that many photographers utilize. All of them, when used properly, can help to improve your results and are great options to make use of. Make sure to choose high quality filters and as always, spend time experimenting with what works for you.