Although I feel a tripod is the most useful accessory for camera users, filters are also near the top of any list. There are those that feel editing software such a Photoshop, Photoshop Elements, or free editing software such as Picasa from Google, Gimp, or IrfanView can replace filters, but there are a number of places where the filter works better if placed on the camera lens when making the exposure.
Most lenses for DSLRs have threads on the front so that filters can be screwed onto the lens. Although some point & shoot cameras also have threaded lenses, most do not. It may take some experimenting to come up with a method of placing a filter over a non threaded lens, but the result can often be worth the trouble. One advantage of the smaller diameter lens on most point & shoot cameras – filters increase in cost with increasing diameter. For example, at B&H Photo (a popular internet photography store) a 40mm polarizing filter sells for about $18.00. A 72mm from the same manufacturer goes for around $100.00.
When shopping for filters, you will find a wide range of prices between manufacturers. Like lenses, a filter may be coated, constructed of better or poorer quality glass (or even plastic) etc. I wouldn’t invest in the best quality filter to use with inexpensive lenses, however if you are using pro lenses you don’t want to degrade what you paid for with a cheap filter.
One way to save money when purchasing filters is to determine the largest diameter lens you have, purchase filters to fit it and, rather than also purchasing separate filters for your smaller diameter lenses, purchase adapter rings. These can be used to step down the filter to the lens and are far less expensive than individual filters. Of course this means carrying the larger filters even if you are only packing the smaller lens, so if you are traveling as light & compact as possible, it may be worth purchasing filters to fit your most used lenses.
One of the most useful is a polarizing filter. This filter can be used to add detail & darken skies, limit reflections, and improve the transparency of a stream, pond, or other bodies of water. Although most are circular polarizing, there are straight polarizing filters available. If your camera uses autofocus & autoexposure (most do) be sure to use a circular polarizing filter or you may find your autofocus and camera’s metering systems not working properly. More information about the differences is at Cokin Filtering Systems. A couple of things to be wary of when using polarizing filters:
- If you are using a wide angle lens the additional “blue” effect the filter provides will vary across the image. (An example which I have to admit I took…)
- Some types of glass or plastic will show stress checking or blotches of color when viewed with a polarizer. Most airplane windows exhibit this effect as do the side windows of many automobiles. The effect may not be noticeable until the image is viewed full size, so be sure to take some images without the filter.
- Depending on the angle of the sun, the filter may have no effect. If you are using the filter to darken skies, try to position yourself so that the sun is at a 90° angle to the subject.
- Although this is obvious if you thing about it, don’t wear polarized sunglasses when photographing with a polarizing filter on your camera. The combination at the right (or maybe I should say “wrong”) angles can completely blacken the viewfinder!
My next most useful filter is the Neutral Density Filter. If you don’t have any reason to take long exposures under bright lighting conditions, you won’t need one of these; however if you are a waterfall addict like me, at least one is required. A ND filter simply cuts down the amount of light that passes through it. Unless specifically designed to do so, it should not alter the color temperature or white balance of the light. There a bunch of different methods of describing how much light ND filters hold back. Some manufacturers use an Attenuation Factor 2, 4, 8, 64, while others may describe the same as Optical Density 0.3, 0.6, 0.9, and 1.8, or by f stops 1, 2, 3, 6.
When you find that stopping down as far as your lens will allow doesn’t let you use a shutter speed slow enough for the effect you want adding an ND filter will help. I have also used them when working with powerful flash units that can’t be “turned down” to allow large enough lens openings to limit depth of field and soften the background behind a subject, or on bright days when I need to control depth of field to defocus backgrounds I can’t compose around. I have a ND 8 ( 3 stops) & a ND 64 (6 stops) – if I could only have one, it would be the ND 64.
A couple of tips when using ND filters: If you are using your camera’s metering system (autoexposure) be sure to cover the viewfinder eyepiece when determining exposure. If you don’t, enough light will leak in (since you have the camera on a tripod & your eye isn’t covering the eyepiece) to give you an incorrect exposure. Some cameras have a built in door, others may include a eyepiece cap. If you don’t have either, a bit of electric tape will do.
If you are using an ND 64 filter, you should compose your image prior to adding the filter. The view finder will be very dark once you attach the filter. You may also have to switch to manual focus – there may be too little light for the camera focusing system to work. One trick I have used comes from my view camera days – keep a light proof cloth that will fit over the camera & your head, and use it to block out all but the light coming throught the viewfinder. This will make it easier to see with the filter in place.
ND filters are also available as a “split” or “graduated” ND filter. A graduated ND filter is just what its name implies – one half of the filter cuts down the amount of light passing through it, the other half is clear. These are also measured in density or stops and are useful when part of the scene you want to photograph is much brighter than the rest of the image. Typically, this occurs with skies in landscapes. If you expose for the sky, the ground is underexposed. Exposing for the ground ends up burning out the sky. By placing a graduated filter over your lens & placing the dividing line at the horizon it may be possible to properly expose both. A couple of problems:
- Since most round graduated filters are split at the center, it forces you to place the horizon at the center of the frame, breaking the rule of thirds.
- If you are including things like trees, mountains or other vertical subjects in your image, the graduation will become obvious since the vertical object doesn’t line up with the split.
The solution to the first is to use something like the Cokin system – it uses square filters that fit in a mount attached to the front of the lens. The filter can slide up & down in the mount, allowing more flexible composition. Lee filters also produces compatible filters – both of these use plastic for most of their filters. If you can afford it, Tiffin makes glass filters that fit some of the Cokin & Lee systems. By the way, every type & color of filter is available using this system. Some photographers use it in place of screw on filters for all their filters. Graduated ND filters are also available with a variety of “tints” that warm or cool the overall image. One last variable – the dividing line between the clear & ND sections of the filter can be either hard or soft. There are advantages to each, however I’d start with a hard division. It won’t look as hard a division as you would expect because it is close enough to the lens that it is out of focus, and will be easier to line up with horizons than the soft division. Check Rod Barbee’s article for more information on using split ND filters.
By the way, in a pinch, two polarizing filters can be combined to make a ND filter. As you turn the outer filter the image will darken & lighten. Sounds like a great way to make a variable ND filter (and one manufacturer Singh Ray sells one) however it is difficult to control color shifts and provide an even density across the entire filter, so I’d only try it in an emergency.
You may be asking why I have not mentioned UV or Skylight filters since they are probably the type most often purchased by photographers. If you are taking pictures at 15,000′ they may be necessary, but most photographers purchase them to “protect” their lenses. My personal opinion is they are a waste of money and will degrade your images. Only stick another piece of glass in front of your lens when absolutely necessary! The coatings on modern lenses will hold up to careful & proper cleaning; sticking an inexpensive filter in front of your lens will often result in additional flare, softer focus, and, when you want to add one of the filters described above, the problem of removing a filter that may have “frozen” to the lens since it hasn’t been unthreaded in years. Filters often become stuck because the pressure necessary to get them to turn distorts the threads. They sell filter wrenches that will help remove stuck filters; a quick & dirty substitute is a rubber band. Fit it around the filter and use it like a oil filter wrench to remove the filter. This Photo.net article offers some additional solutions for stuck filters.
Color temperature or white balance correction filters are useful, however since digital cameras can change white balance between exposures, not as necessary as they were with film. Unless you have a specific lighting condition that you need to repeatedly correct for, I wouldn’t invest a lot of money into them.
Although there are many filters designed for black & white photography, and they will allow better exposures if used on digital cameras for planned black & white images, most editing software will duplicate the results almost as well. Again, like the color correction filters, I wouldn’t invest in many of these unless I had a specific reason.