Essential filters

 

Filters are sheets of glass or resin that you put in front of your lens to alter the light hitting the sensor. They come in two formats: round filters are meant to be threaded on to the front of the lens, while square or rectangular ones must be used in conjunction with a filter holder system, such as that manufactured by Lee or Cokin.

If you’re interested in landscape photography, there’re a few filters that I can’t urge you enough to invest in.

Neutral density filter

ND filters are dark pieces of glass or resin that reduce the amount of light entering the lens, and come in various strengths. Different manufacturers use different nomenclature, but as a general rule, .3ND results in 1-stop light reduction; .6ND is 2-stop; .9ND is 3-stop, and so on. For creative effects, you can’t beat a 10-stop ND, but keep in mind that this reduces light so much that it’s extremely difficult to focus with this filter on. If there’s a slight breeze, you can extend the shutter time to capture clouds as streaks, as in the following photo. With an interesting foreground (which is severely lacking in this example), you can turn an ordinary photo into a very interesting one with an ND filter. You may be able to achieve the same effect with Photoshop layers, but it’s going to be a lot more work than getting it right in the field.

Graduated neutral density filter

A good set of GND filters is an absolute necessity for landscape photography. Take a look at the photos below.

Unlike ND filters – which block light everywhere in the frame – GND filters block light selectively. There’re three types of GND: soft-edge, hard-edge, and reverse, shown left to right below:

Soft-edge GND have gradations that slowly transition to clear, and should be used where the horizon isn’t well-defined. Hard-edge GND have more abrupt transitions to clear resin, and are your best bet when the horizon is well-defined. Reverse GND are more expensive, but there’s a good reason to use them: when the sun is near the horizon, you want to block its light the most. The sky higher up the frame is already a bit dark, so don’t want to darken it even more.

In the sample photos above, the one on the left was taken with GND properly aligned with the horizon, while the one on the right was taken without a filter, and with the exposure set for the lake instead of the sky.

As with ND filters, GND come in varying strengths, but the most common ones are 1, 2, and 3-stops.

As an alternate to these expensive filters, you can take multiple photos, with different exposures for the foreground and background, and merge them in Photoshop or Photomatix, but this won’t always work. For example, if it’s a windy day, clouds, leaves, and waves will have traveled between your photos, and merging them will be a nightmare. On the other hand, there’re many cases where you must use exposure blending instead of GND filters – for example, when the horizon isn’t well-defined: you don’t want the top half of the tree to be darker than the lower half.

Circular polarizer

I’ll have to take some with-filter and without-filter photos to show you the effect, but in essence, a circular polarizer cuts glare and enhances colors and contrast. Use it on an overcast day to reduce the ugly gray sheen on leaves and flowers; use it on sunny days to make clouds pop, and darken the sky; use it in the fall to make your reds more vibrant by cutting reflections (this isn’t the same as increasing saturation in post-processing – it’s about removing unwanted reflection from objects). Of all the filters discussed here, this is the only one that you can’t replicate in Photoshop.

This filter is usually round, and has a movable front that you adjust to select varying amounts of polarization. The effect is most pronounced when your camera is pointing 90 degrees away from the sun; a word of caution though: wide angle lenses cause the sky to be darkened in varying degrees, so you might not want to rotate the filter to its full extent.

Filter systems

You can buy either round filters that you can attach to the front of your lens, or you can buy rectangular ones. A word of caution: before you head out and spend a fortune on filters, check if the front element of your lens rotates when focusing. If it does, using filters will be a much more difficult task than if your lens has an internal focusing mechanism. The problem with lenses where the front rotates during focusing is that if you’ve attached a filter, it’ll move when you’re focusing, and if you’ve already spent quite a bit of time aligning the filter properly, you’ll need quite a bit of patience to set it again after focusing, and then focus again! This problem crops up often on cheaper lenses, so before you buy new lenses, always use your favorite search engine to determine if the model you’re looking at has a rotating front element.

That said, I recommend that you get a round circular polarizer (check your lens documentation to see what size you need) that you’ll thread to the front of the lens, but you must get a rectangular GND. Here’s why: you saw above that a GND is half dark, and half clear. If you get a round GND the size of your lens, you’ll be forced to take photos where the horizon is smack in the middle of the frame, which will make for a horrible composition! Rectangular filters allow you more leeway as far as composition is concerned.

To use rectangular filters, you need a mechanism to attach them to the lens. I use the Lee Foundation Kit in conjunction with Lee 4″x6″ rectangular GND filters, and 4″x4″ ND filters. For circular polarizers, you can’t go wrong with B+W. There’re many other brands available, both less and more expensive than what I use, and ultimately your budget will define what you should get.

To use the Lee filter system, you attach a ring to the front of the lens; to this gets attached the actual filter holder. You then slide in the GND or ND filter from the top. While looking through the viewfinder, I usually move a horizontally-aligned finger up and down to determine exactly where the transition from dark to clear is, and then adjust the filter accordingly. Take a look at the pictures below to see how this filter system works.

No filter system attached

Lee filter system 77mm wide-angle ring attached

Lee filter holder attached

Lee 4″x6″ GND inserted

The Lee filter system can also be used with a circular polarizer; for this, a 105mm ring gets attached to the front of the filter holder (see lower two photos above), and to this you screw on a 105mm circular polarizer, as shown below.

When attaching accessories such as filter holders to your lens, there’s always a risk of vignetting, which is the darkening of corners. To a certain extent, you can fix vignetting in post-processing, but dark areas are already noisy, so when you increase exposure in these areas in post-processing, you’re making the noise in the corner of your photo unacceptably bad.

With the above setup (Lee 77mm wide angle adapter ring + Lee filter holder system with 2 filter slots + Lee 105mm ring for the polarizer + Lee 105mm circular polarizer), I see severe vignetting with my 17mm lens on the full-frame Canon body that I use. The vignetting disappears around 20mm, but since I often shoot at 17mm, I can’t attach the circular polarizer to this lens.

However, if I remove the 105mm ring for the polarizer, and the 105mm polarizer, but instead add a third filter slot (the Lee foundation kit comes with 3 filter slots; I removed one to install the ring for the polarizer), there’s no vignetting at 17mm on a full-frame sensor.

ID: filters