Neutral density filters help you achieve extreme long exposures, while graduated neutral density filters help balance exposure between a bright sky and a dark foreground. Both were used in this image. The exposure time was three minutes.
For most photographers, their first experience with a filter is when it is suggested they purchase a UV or Skylight filter to protect their lens. It’s usually much later that beginning photographers find out about the other filters available to them, and what they can be used for.
Once you’ve decided to add a filter or filters to your camera bag, however, you’ll be faced with a myriad of choices regarding the various brands, materials, and types of filters that are available to you. Many times, the gut instinct is to purchase the cheapest filter that will do the job. The reality is, however, that there are many factors to consider when purchasing a filter, and buying the cheapest one on the rack that does what you want, it to is not usually a good idea. There is often a difference in the quality of the materials used, even when both filters appear to be made of the same things.
In An Introduction to Filters for DSLRs, you’ll find a breakdown of the different kinds of filters, and their uses. Here, I’d like to try and demystify the differences between filters, and why similar looking filters might have drastically different price points.
Screw-in versus drop-in filters
First of all, there are two basic types of filters: screw-in and drop-in. The former mount directly onto the lens via the threads on the front, whereas the latter drop-in type are square or rectangular in shape, and require a filter holder and mounting ring that attaches to the front of the lens. Certain types of filters are available as both a screw-in and drop-in filter.
Screw-in filters are constructed of glass with a metal ring. The quality of the glass can vary, even within the same brand, depending on whether you’re going with a high end filter or a value priced one. The metal of the ring can vary as well, as they can be made of brass or aluminum. Cheaper filters usually have an aluminum ring. It’s a soft metal that is more easily dented if dropped, or bent if put under pressure. This could cause the filter to jam when mounting it to your lens. The most popular screw-in filters tend to be polarizers, UV, and neutral density filters.
The other type is what’s known as a drop-in filter. These are square or rectangular pieces of glass that are typically inserted in a holder that is mounted onto the lens. Often, the holder, or mounting ring, can also accommodate a screw-in polarizing filter, as well as two or three drop-in filters in front of that, allowing you to combine the effects of a polarizer, a neutral density filter, and/or a graduated neutral density filter.
While graduated neutral density filters are available as both a screw-in or a drop-in, the drop-in style allows for more precise placement of the gradation, and thus allows for more creativity. Drop-in filters are generally part of system, or have compatibility with one. Some examples include: the Lee filter system, Vü Sion Q system, Formatt-HItech, and Cokin P and Cokin Z filter systems. You’ll want to ensure that the system you invest in has the filters you need available, and that it’s compatible with your size camera.
Materials used
You may notice when shopping for filters, that there is a wide range of prices, for the same types of filters. The primary difference in cost is related to the material used in the filter. Other materials used to make filters include optical resin, which is more of a plastic material, and polyester. Polyester filters are generally used for color correction or soft focus effects, while optical resin is used as a more cost effective option compared to glass, especially in the case of drop-in filters such as graduated neutral density filters.
The more expensive filters often use a top quality glass, such German Schott Glass, which is generally color neutral and distortion free. Some filters by their nature need to be made from glass, such as polarizers. The differences in the material are related to the chemical makeup of the glass, thickness, and coatings used. Where thickness is concerned, the thinner the filter the better, as thinner glass reduces any possible distortion.
A polarizing filter not only helps make the sky bluer, but also controls reflections on shiny surfaces, such as buildings.
In the case of polarizers: in cheaper filters, the polarizing material is sandwiched between glass; while the polarizing material is bonded directly to the glass in more expensive ones. This reduces the chance for air pockets, and other irregularities that could affect the image quality in a negative way. Again, the quality of glass can vary widely between a budget-priced filter, and top quality one.
I have used both high quality glass filters, and optical resin ones. While the glass is more fragile if dropped, it tends to resist scratching more effectively than resin. However, optical resin can be considerably less costly than glass, for the same type of filter. For instance, a Formatt Hitech 3-stop soft edge graduated neutral density filter lists for about $80, while Vü Filters 3-stop Soft Edged Graduated Neutral Density Filter, which is made of Ultra White German Schott glass, retails for $224. There are different grades to optical resin filters as well. This Lee 0.9 (3-stop) Soft ND Grad Filter, made from optical resin, lists at $146.
While any of these filter will provide good results, with higher end lenses, you may notice a distinct difference between a higher quality and thus higher priced filter, and one that cost less.
Coatings
In the days of film, filters did not need to be coated in the way they do for the digital age. Film was a more forgiving medium, which didn’t pick up flare or reflections the way a digital sensor does. For this reason, multi-coatings have become incredibly important in filter manufacturing. Higher quality filters will use these coatings to reduce flare, and increase light transmission. An uncoated filter will suffer from a loss of light. Some filters have a single coating, which is better than nonr, but not as good as a multi-coated filter. For digital if you were to take the same shot three different times, with an uncoated, a single coated, and a multi-coated filter, the difference should easily be visible in the image. In addition to minimizing flare and increasing light transmission, coatings also help maintain good contrast and color reproduction. Filter manufacturers will also use coatings that help make the filter easier to clean, and more scratch resistant.
Many photographers will debate whether or not filters are necessary, with those who say no doing so out of fear that the filter will degrade image quality. I use filters often, especially in my landscape work. There is no true digital substitute for a polarizing filter, and neutral density and graduated neutral density filters provide for effects not easily duplicated in post-processing. The key is to ensure you are using a quality filter, that is free from color shifts and distortion, and properly coated for digital. I’m not saying you have to spend top dollar on a filter, just understand what the differences are, so you can make an educated decision.
A drop-in filter system allows use of square or rectangular filters. This is advantageous when using graduated ND filters, so you can adjust the placement of the gradation.
So do you own and use filters? What buying tips do you have for newbies? Which are your go-to and favorite filters? Please share in the comments below.
