Neutral gradient filter

[asterismos]

I have lots of filters given to me by my father and recently I have been experimenting with alot of them. I have been reading in the forum about a neutral gradient filter or ND filter.

What is the main purpose of this kind of filter and how does it compare to a polarizer? Also what kind of markings would be on the filter to identify it? I have over 20 filters (some duplicates) that my father gave to me and I am trying to figure out what they are and how best to use them.

Thanks for all your help!

[PKMax]

an ND filter (neutral Density) are designed to prevent some light getting into the camera, which will allow you to do things like extend the shutter time when it's too bright to do time exposures. Like if you wanted to do a time exposure during the day in a street to blur all the people walking past, but there is too much light to be able to get the shutter speed slow enough even with the aperture on the smallest setting. so adding one or more ND filters will cut down the light coming in and require that you increase your shutter speed to compensate.

Then you have the ND Gradient, which is similar to above but it's a gradient from dark through to clear, half and half of the filter. the reason for these are so that you can take a landscape for example, where the sky is too bright, so exposing for the ground gives you an overexposed sky, and exposing for the sky gives you a underexposed ground. so using a ND gradient you can cut down the light coming in through the half that you want to underexpose a little (like the sky) and have a more even exposure.

also, the markings on an ND filter would be something Like ND 1, ND 4, ND 8 etc.. where the number indicates their strength (larger number, the darker it is) I think the number relates to the Density of the filter.. but that number translates to an fStop reduction somehow. ie ND1 is a about 3 stop reduction, ND4 is a 13 stop reduction.

Polarizing Filters to have the effect of cutting down the amount of light that comes into the lens, but this is just due to the way they work.. they "convert" unpolarized light into polarized light, Light waves generally travel in all angles, especially when being bounced off all those objects you see. so a Polarizing filter allows you to remove the light that is travelling at a certain "plane" so when bounced of water the beam will be travelling towards your camera in a horizontal fashion, so turning the polarizing filter can prevent this light getting into the lens. it's easy to see the effect of a polarizing filter by turning it around in front of an LCD monitor, because they only put out polarized light. so turning the polarizer to a point will cause the screen to look black through the filter because it will have filtered out all light coming from the monitor.

Polarizers are used to reduce the glare from things like water, glass. and also they make skies blue-er and colours generally more saturated.

[asterismos]

Thanks PKMax!

Apparently I don't have any of these type so I will have to look into getting some as I think they could be really useful. I do have a polarizer and some others like a diffuser and a SFT which I think is a soft focus filter and more than several colored filters which i have been told are useful when taking B&W shots (although not really sure yet how to put them to use as they are only supposed to subtly change tones).

[PKMax]

I actually have a massive collection of filters (handed down by my grandfather ) and I recently decided to sort through them to work out what would actually be useful filters to carry with me at all times, after a lot of sensible thinking, I put most of them in a bag under the bed heh.. most filters can be replicated easily on a computer, light the warming or cooling filters.

so the only filters I now carry with me:
UV Filter - Just to protect the lenses really.
Polarizer
ND4 and ND8 - I have used these quite a lot outside to get me a long shutter
Gradient ND - I've not actually used it yet, but think I might one day lol.
IR Filter - Cause it's fun :) (although it doesn't Filter IR light, it only lets IR light in, so it's really a Visible Light Filter :) hehe)

That's about it really, I have all sorts of odd ones, like starbursts, softening etc, but tend to replicate those things on the PC, mainly because I think I'd like to have the choice later on to actually use a sharp image etc.