Camera len filters have many uses besides the obvious of protecting your expensive investment – your lens. Besides that, every serious photographer should know his choice of filters and how it helps to reduce glare and improve saturation. This article is a primer to the filter and understanding what are they and what they can do.
Linear & Circular Polarizers
Primary Use: Reduce Glare and Improve Saturation
Common Subject Matter: Sky / Water / Foliage in landscape photography
Polarizers is one of the most important filter for landscape photography, like all filters, it reduces the amount of reflected light falling on your camera sensor, and as such, it will appear deeper blue, and reduce glare and reflections off water and other surfaces hence reducing the ‘soft box’ effect on subject. It will also reduce the contrast between land and sky.
How this is done, by rotating the filter in how the camera is positioned to and the position of the sun in the sky. The effect is the strongest when your camera is aimed in the perpendicular to the direction of the sun light. However, the use of this filter will dramatically also reduce the amount of light reaching your camera’s sensor often by a 2-3 f-stops and this means the risk of a blurred handheld image goes up dramatically, and may make some action shots impossible. And also, the use of this filter on a wide angle lens can result in an uneven toning of the sky from one end to the other. Circular Polarizer is designed so your camera’s metering and autofocus will still function while on the other hand, linear polarizer are much less expensive but cannot be used with TTL metering and autofocus.
Neutral Density (ND)
Primary Use: Extend Exposure Time
Common Subject Matter: Waterfalls, Rivers, reflection off water under bright light.
ND Filters are one of the most commonly used with a sufficiently long exposure time that is not attainable with the possible range of apertures at lowest ISO. Some of the most commonly used situation where ND Filters are being used are smoothing water movement, achieving a shallower depth of field in very bright light, reducing diffraction by enabling a larger aperture, making moving objects less apparent or not visible, and introducing blur to convey motion with moving subjects.
A simple table for you to find out which ND Filter you need to get.
Technical note: each stop of light reduction corresponds with halving of light. A given strength therefore passes only 1/2 strength of the initial light, where strength is the filer strength in stops. Example: 3-stop ND only passes 1/8th of the light since 1/2(3) = 1(2*2*2) which is 1/8th.
Graduated Neutral Density (GND)
Primary Use: Control strong light gradients and reduce vignetting
Common Subject Matter: Dramatically lit landscape
GND or Graduated Neutral Density Filter restricts the amount of light across an image in a geometric pattern. This is also called Split Filters (as in the Film photography days). Ideally used in landscape in a linear blend from dark to bright. GND is essential when trying to capture dramatically lit landscape such as a sunrise or sunset scenery. One of the most commonly used setting for GND is the differential setting of how much light is being let in one side of the blend versus the others as shown above 0.6 ND Grad refers to the ND Filter which lets in 2 f-stops less light (1/4th) at one side of the blend, and similarly, a 0.9 ND grad lets in 3 f-stops less light (1/8th) at one side. Most landscape photos need no more than a 1-3 f-stop blend.
Reversed Graduated ND Filter: This is one of the relatively new in the filter technology. When compared to regular hard/soft-edge GND Filters, they are dark at the horizon and graduated soften towards to the top. Reverse GND filters are very useful for sunset shots when you shoot against the sun and it is near the horizon. A common problem with such sunsets is that the sun is much brighter than the sky. If you use a hard-edge GND Filter, the sky might get too dark and if you use a soft-edge GND filter, the sun will be overexposed. The solution is to use a reverse GND filter, which balances the sun and the sky in the frame, resulting in a more balanced exposure.
UV / Haze Filter
Primary Use: Improve Clarify with Film and providing lens protection
Common Subject Matter: Any
Nowadays UV Filters are usually used as a protection for lens since they are clear and will not affect in anyway the image. However with film camera, UV filters reduce haze and improve contrast by minimising the UV light that reaches the film, and this will not affect digital sensors as digital sensors are nowhere as sensitive as film. On the other hand, UV filter has the problem of increase lens flare and hence decrease image quality.
Warming and Cooling
Primary Use: Change White Balance
Common Subject Matter: Landscape, Underwater, Special Lighting
Colour / Warming / Cooling filters are generally used to alter camera white balance. There are two types of colour filters – colour correction and colour subtraction. The former is used for correcting white balance, while the latter is used for absorbing one colour while letting other colours through. These are very familiar with some of the filter that is inbuilt in some of the camera today,.