Sunday, March 25, 2012

Usage of Filters

Ever since digital photography became popular the usage of filters has significantly gone down. With a photo editing software, you can for the most part simulate the effect of a filter. On a personal note, I prefer to take photographs rather than sit on the computer editing.

My personal preference aside, there are times when you would need to use a filter. Taking nothing away from software the effect of these two filters cannot be re-created in software. The first one is a UV filter and the second one is a polarizing filter. There is another filter you might want to consider if you are into extended exposure which is a neutral density filter but this is not always required.

Before we proceed we need to know one thing about Sun light. Apart from the spectrum of light we can see, there is a spectrum of light, which we cannot see. These include ultraviolet (UV) and infra-red (IR) rays. Most modern day digital cameras have an infra-red protection shield on the sensor to protect it. (More on infra-red photography on later post). However, there is no filter for UV, which is fine. Why you may ask. The reason for that is, the glass in your camera lens cuts out UV. The more number of layers light passes though the more UV gets cut out. So you may ask why do you need a UV filter. Well there are two reasons. The first one is, not all the UV gets cut out on its way to the sensor. This is especially true on cheaper lenses (mostly the kit lens) where plastic elements are used instead of glass. So to cut out the UV would need a UV filter. On the more expensive piece of glass, you can get away by not using a UV filter. Fore the more expensive glass you would use a UV filter for the other reason. To protect the front element of your lens. That is an expensive piece of equipment and you don't want a scratch on that!!! (You might consider it when you are doing street photography or a wedding)

So what impact does the UV have on the images you might ask. UV shows as haze on your images take on clear sunny day, which I might add, you just can'r remove in post processing. The only way to reduce it is to do a levels adjustment ( levels adjustment....perhaps a blog post for some other time). A UV filter won't cut out the haze if it is a hazy day, it will just stop it from coming on a regular day.

The other filter you need to have is a polarizing filter. There are two types here Linear Polarizing Filters(LPL) and circular polarizing filters. If you using digital cameras you need a Circular Polarizing Filters(CPL). There is a technical reason for this (A simple search would give you the reason when LPL does not work on a digital camera.) CPL as a filter allows light to come into the camera only at an angle. This is an effect which cannot be re-created at all in software. (CPL also cuts out UV too, so you don't need to use CPL and UV together [Using filters one behind the other is called stacking filter])  The few places you can use it are to make your sky's bluer, cut out the reflections from the water or if you want to shoot a subject below the water. Perfect if you are shooting  lakes and water bodies. In the image below the glare of the sun was cut out by using a CPL. If I had not used it, there would been a lot of glare off the surface of the water making the water look more white than blue


This can also be used in case of windows or any reflective surface to cut the angle of light. A word of caution though when using the CPL with ultra wide angle lenses. You run the risk of making the sky look extra blue or almost night like in a day shot. You can also use a CPL on a cloudy day when there is a lot of grey in the scene to get more vibrant colours

Picking a filter. If you go about searching for filter you would find these range from the really cheap to mighty expensive ones. The more expensive ones are better because they are extremely thin and have a negligible impact on the quality of image. [It is piece of glass and glass refracts light (no getting away from physics).]
They also come in different MM threads which get screw on top of the lens. Now if you have different lens threads then buying a sheet is a better option and buy different holders (cokin filters is one such option). You can use this for CPL but you might want to consider buying a different UV for each lens. These are one time investments and last a lifetime.