Cokin Filters Explained
Cokin Filter Systems
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This consists of a range of square filters of various functionality which are held into place in front of the lens by a holder attached to a threaded adapter ring.
The holder allows the user to slide various filters into place and even stack filters together. This holder is then attached to the lens via a threaded ring with a diameter to match the filter thread of the lens.
The major benefit of this system is that the holder, along with the collection of filters can be attached to different lenses by changing only the adapter ring.
This works out to be far cheaper than having traditional screw in filters which need to be bought specifically for each lens size.
The 4 different classes of filters
The filters are manufactured from high quality CR39 organic glass. Cokin produce 4 different sizes of filter known as 'A series', 'P series', 'Z-pro' and 'X-pro'.
The A series are primarily for use on compact cameras and camcorders.
The most popular range is the P series which are suitable for 35mm SLR photography, both film and digital.
the P series are intrended for lenses down to about 20mm or 24m. Any wide than this and the edge of the filter tends to creep into the shot.
The Z-Pro range measure up to 100 x 150mm and are designed for use on medium format cameras as well as 35mm SLRs with lenses wider than 20mm to cover the greater field of view. Obviously intended for landscape shots and wider more panoramic vistas.
The X-Pro range is larger still, 170 x 130 mm and is designed for medium and large format cameras.
Lens filters in the digital age
How has Adobe Photoshop effected the use of filters
With the advent of digital photography and the use of photo manipulation software many traditional filters have fallen out of favour. In particular coloured filters, commonly yellow, orange and red, as well as warming and cooling filters are less popular than with film as these effects can easily be replicated via software. There are still plenty of filters that are useful with digital cameras. The most popular are probably, Neutral Density, Graduated Neutral Density and Polarisers.
Neutral Density Filters
Cutting down on exposure
These filters have a neutral grey tone to them and are designed very simply to cut the amount of light that passes through the lens. A photographer would use them when they want to use a longer shutter speed than is ordinarily possible due to the brightness of the conditions. For example, if you wanted to photograph a river during the day, you may wish to use a shutter speed of a second or more to achieve the effect of flowing water. During the day this may not be possible. If you are shooting at the lowest ISO setting available and are at minimum aperture you still may not be able to achieve a suitably long exposure. By adding a neutral density filter you can reduce the light transmitting to the camera and lengthen your shutter speed. ND filters are available in a range of strengths depending on how much you wish to cut out the light. A good quality ND filter shouldn't affect the colour of the light as it passes through, only the intensity.
Graduated Neutral Density
Gradual changes in exposure
Similar to ND filters above, GND filters are designed to reduce the light passing through the lens. The difference here is that the filter is not uniformly dark. One half of the filter will be clear with the other half darker. You can have a 'hard edge' where the transition is a solid line across the middle or a 'soft edge' where the transition from clear to dark is gradual. The reason for these filters is that you can balance the light across a scene to record more detail when the dynamic range would ordinarily be too great for the camera to record in a single exposure. For example, you may have a landscape where the sky is bright and the foreground relatively dark. If you expose the foreground correctly then this may result in the sky being 'blown out' with no detail recorded and just a mass of white sky. By using a GND, you could position the dark portion over the sky with the transition to clear falling over the horizon. This will reduce the brightness of the sky so that it more closely matches the foreground and can be recorded in a single exposure. It is of course possible to take two photographs with different exposures and then blend them during post production but this can be time consuming and I personally feel it is more satisfying to get the image right at the time of taking the photograph.
Cutting down reflections from non metallic surfaces
There are two types of polariser; Linea and Circular.
Linear polarisers are cheaper to manufacture but they can affect a camera's metering so circular polarisers are a more popular option. Both types are used for the same two puroses: to increase saturation of colours, specifically blue skies and green foliage in a landscape, and to cut reflections from non-metallic surfaces such as glass and water.
If you are shooting a lake or river then a polariser would mean you can shoot through the surface of the water and see beneath the water. If you were shooting interiors or architecture then a polariser would allow you to shoot through glass windows and tables. A photographer may be wanting to shoot the exterior of a shop's display and the polariser would allow them to do so by removing the reflections of the street outside and indeed the photographer himself from appearing on the glass of the window. This is an effect that can't be replicated through software.
Holder and Adapter rings
Using filters together
As mentioned above, the main advantage of this system over screw-in filters is the ability to use the same set of filters with more than one lens size.
If we take the P series as an example then there are two common types of holder, the regular holder and the wide-angle holder.
The regular holder can take 2 square/rectangular filters as well as a circular filter such as a polariser so that you can stack filters for different effects.
The wide angle holder has only a single slot but the holder is lower in profile which means it is suitable for use on wider angle lenses by minimising vignetting. If you are using lenses wider than about 24mm in 35mm format then the wide angle holder is recommended.
These holders attach to the lens with the relevant adapter ring. The rings come in a range of sizes from 48 to 82mm in diameter and are named logically. A77mm ring is called a P477, a 62mm ring is called P462 and so on.