The best filter you can buy for landscape photography is the neutral density graduated filter. Cokin have created a bundle of three essential ND grad filters in the P series which is perfect for most primes and modern zoom lenses.
The kit comes with a P-Series Filter Holder, P121L NDx2 Filter, P121M NDx4 Filter, P121S NDx8 Filter and supplied with a Cokin 100 Page Filter Catalogue. You will then just need a filter holder adaptor for your lens. P-series adaptors are available in sizes from 48mm up to 82mm.
You can buy the Cokin ND Grad Kit here: Cokin H250A ND Grad Kit
The ND filter is one of the more useful additions to the filter bag. Digital image processing can do many things but it can’t reduce the light reaching the film or CCD. That’s the job of the camera’s exposure system and an ND filter throws in a helping hand.
The name explains its purpose. It’s neutral (in colour) and it has a density (level of opaqueness)
Neutral Density filters come in a range of densities. The basic ND2 is 2x exposure factor (or one f/stop) and an ND4 is 4x (two f/stops). There’s also an ND8 (8x or three f/stops) and a less common ND64 (64x or six stops).
The filter goes over the lens and reduces the light reaching the film by the exposure factor of the filter.
If for example you had an exposure of 1/125sec at f/11 and you added an ND8 the shutter speed would reduce to 1/15sec or the aperture would need to be opened to f/4.
The reason to use an ND filter suddenly become obvious. If you want to force a slow shutter speed, for motion blur, or you want the lens at the widest aperture, for shallow depth-of-field, the ND filter can help.
It can also be used in combination with a flash to effectively reduce the guide number for close range photography.
The ND2 is hardly worth bothering with so we’d suggest you’re first ND filter be a ND4.
