Introduction… What are filters?
You own the perfect lens and create stunning images, is it possible to make those pictures even more wonderful? You might find the answer to this by using a filter. Filters are accessories that are added to the front of your lens that emphasize, eliminate, or change the colour density of the image. Typically made out of glass, resin, or polyester, the transparency of the material allows for correction of light or colour balance. Want a special effect? Many filters are designed to add bursts of colour, soften edges and make light sources sparkle.
Attaching these filters is easy and quick, there are two styles available in the market. Screw in or threaded round filters are glass or plastic disks with a metal or plastic threaded ring frame. These are simply screwed in to the front of your lens. Available in different sizes, most filters types will be available in your lens size. Compact and ultra portable, these screw in filters are slim in design and can be stored easily. A common disadvantage of this type of filter is that you will need to purchase several filters for every lens size you carry and in every filter type you require.
Screw In (aka Lens Glass) Filters »
Drop in filters come in square or rectangular shape and a filter mount is required for it to be used with the lens. Although bulkier than the screw in variety, you will only need to purchase one mount per lens size and one of each filter type you require as they are interchangeable between mounts.
Drop In Filters »
Understanding the different types of filters will allow you to manipulate, correct colour, add effects, and enhance your images prior to print. So the big question is, why don’t you just add these effects in editing software like Photoshop afterwards? Although it is possible to colour correct and add special effects to your images after shooting, it takes much more time to do this then using a filter in the first place. There are even some corrections that are done through a filter that are nearly impossible to replicate in digital software applications.
Construction… How are filters made?
Glass
The main component of screw-in filters their glass construction. The price range can vary depending on the process to which the filters are produced and is unique to each manufacturer.
Filters can be constructed out of regular glass that sandwiches a coloured gel in-between. This lamination process fuses the three pieces together and is cut and ground to specific filter sizes. The disadvantage is that the layers may separate over time causing bubbles and imperfections. And because there is so many layers involved, all 6 surfaces of the materials need to be perfectly flat or else the image quality can be reduced. Over time, the gel in-between the glass can also fade.
Higher end filters use a completely different process. Raw elements are added to the molten optical glass so there is no risk of uneven colour. This molten optical glass is higher quality than regular glass and is ground and polished for a perfectly flat surface. Coatings can be added to both or a single side of the filter to reduce reflections and a protective top coat is sometimes applied to prevent scratches.
Filter Frame
The ring that holds the filter and attaches to the lens is made of brass or aluminum. Brass is a harder metal that is not easily bendable making it nearly impossible for it to become binded to the lens if it suffers from an impact. Although very durable, the hardness could be a disadvantage as any impact of the filter could transfer to the actually lens itself and damage it rather than the filter.
Aluminum is another popular material for the filter frame. It is softer than brass, thus will bend and distort if impacted hard enough. This could save your lens, since the aluminum frame will absorb the impact and possibly break the glass filter instead of the lens. The downside is that the broken glass may damage the lens or the filter frame will fuse to the lens requiring a special tool to detach it.
The metal filter frames are usually black in colour to reduce reflection and minimize distortion.