Fireblade2K4 said:
Just to drop in on this thread, filters...what is their purpose? Am I right in thinking that they help stop blown skies etc when taking photo's where the sky would normally be over exposed, also along with adding different tones to the shot?
I've never used filters but think I could do with investing in a couple if this is what they are for.
Stu
Each type of filter has a different purpose:
Polarisers
Like Polaroid sunglasses they reduce reflections from water etc by only letting light orientated in a particular direction through the filter. The by-product of this is an increase in the saturation of skies etc.
ND (Neutral Density) Filters
Used to limit the amount of light getting into the lens to allow either a longer shutter speed or wider aperture in strong sunlight. They're available in varying strengths based on the number of stops they reduce the light by, normally they can also be stacked to give even more reduction.
Graduated NDs are a special case, only half the filter is coloured, either with a hard edge of a soft blend to clear. These are a favourite of landscape photographers who use them to limit the dynamic range of a shot by darkening the sky to keep the entire scene correctly exposed.
All NDs should be a neutral grey so as not to put a colour cast on the image but some, notably Cokin, can produce a brown or pink cast which can be awkward to remove in PS.
IR Filters
Only allow transmission of near IR and sometimes deep red light. When combined with some basic post processing this can produce some very interesting images (plenty of examples on the forum). Compacts and Nikon DSLRs tend to be best, Canon DSLRs have a very agressive IR Cut filter in the body which means that you need very strong light and 30s exposures for decent results.
Colour Filters
With the advent of digital these are on the way out since the effects are easier to acheive in PS. However for film and especially B&W they're used to subtly shift the colour or contrast in an image by warming, cooling or shiftign the colours in the image.
Effects Filters
There are plenty of other effects available, mainly from Cokin, to add to the basic image - star filters for night shots, soft focus filters for portraits, prisms for multiple images etc.