Put filter into the Ebay search and narrow down to photographic and you come up with hundreds of offers. Buying secondhand can save you quite a bit, but what do you buy and why?
A filter usually has the practical advantage of protecting the front element of your lens from dirt and scratches, plus it is easily replaced if damaged. Many filters in the past were designed to help film cameras record balanced images in different lighting conditions, either warming up or cooling down the final effect. Back in the days of Black and White colour filters were used to excentuate contrast. These days of Digital Cameras, most have programms set to compensate for differing conditions, or the image can be rectified on the PC later. So a filter has two uses, protection and image manipulation.
WHAT DO YOU NEED TO KNOW TO BUY A FILTER
1. Filter size (shown in mm and often marked on the front of the lens), this refers to the diameter of the filter required ie. Standard Canon lenses are usually 52mm and most Canon L series lenses are 77mm, but there can be 58mm, 62mm, 72mm etc.
2. Single thread or double thread. Most are double threaded meaning you can stack additional filters on the front.
3. Rim size. If you are using wide angle lenses the narrower the filter the better as it is less likely to cause vignetting (there is usually a premium on the cost)
4. The Effect you require (examples later)
5. Coating. Unless you are buying the cheapest of filters most now available have a surface coating designed to both cut down glare/flare and to improve light transmission into the lens. The number of coatings and whether on one side or both sides of the filter usually improves its performance but adds to the cost.
SO WHICH TYPE OF FILTER TO BUY?
Basically you need a UV filter or Clear Protection filter for general lens protection, anything else will add a slight colour effect. Look for UV0 or UVN. Skylight filters usually have a slightly warming effect.
Next a Polarising Filter is very useful. Choose a Circular Polarizer (CPL) over Linear Polarizer (The former allows your auto focusing to work without hindrance). This filter when rotated can be used to reduce reflections from shiny surfaces, water, glass, painted surfaces etc. Also when used out of doors it will increase the density of colours especially blue skies, sea etc.
Effects filters. Most filter effects can be added after on you PC if you shoot in digital, but if you still want effects filters go for the square gelatine filters which fit an adaptable holder such as Cokin or Lee. This system can be used on all of your lenses with the adapter ring, plus they are easily stored. Consider the Professional range ( Cokin P ) if you anticipate using with lenses that take larger filters otherwise Cokin A. Cheaper unbranded items are available allowing you to build a collection quickly.
WHICH BRAND IS BEST?
I tend to favor Hoya because they usually offer good value and performance, but for out and out quality you cannot beat B+W.
Hoya produce a range of filters but look out for HMC in the discription (Hoya Multi Coated) and if you need a narrow rim filter look for Super HMC. Newer ranges are designated as 'Digital' there are no real differences but again Digital 1, Pro etc are explained on Hoya's webpage.
B+W Filters made in Germany are also excelent and again there are options. These filters cost slightly more but the MRC coated filters are very easy to keep clean and boast the hardest coatings, (My preference for the best lenses in my collection), along with Sigma, Canon and Nikon filters all offer quality. Over all I would say any filter is better than none for the protection factor, but if your optics are good then you must balance the lens with a high quality filter.
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