neutral density filter?

Question

can anyone help me with this!

ok, I'm going to photograph at night, photographing "traffic trails" through b+w film photography.

I've been advised to use a "netral density filter".

I understand a filter as a little celophane square you use in the darkroom, but i get the impression that this "neutral density filter" is one I acutally put on the camera (somehow?!!?!)

can anyone explain this really simply to me?
what is a neutral density filter?
how do i attach one to my camera?
do you think i should use this filter for night photography, photographing traffic trails?


thankyou sooo much! i swear ill get the hang of photography one day!

Answer 1

A neutral density filter attaches to the front of the lens. In photography and optics, a neutral density filter or ND filter is a "grey" filter. An ideal neutral density filter reduces light of all wavelengths or colors equally. The purpose of standard photographic neutral density filters is to allow the photographer greater flexibility to change the aperture or exposure time, allowing for more control, particularly in extreme circumstances.
However, you don't need to use a neutral density filter if you are using a lower ISO film and especially if you are shooting at night. A neutral density filter works best when you are trying to do long exposures on bright days, or when the lighting is such that you can only shoot with fast shutter speeds. But if you are shooting at night it doesn't make much sense to me unless perhaps you are using 1600 or 3200 ISO film and the shutter speeds are so fast that you can't get do a long exposure.
In fact you are going to exacerbate the effects of what is called reciprocity failure by using a neutral density filter and creating longer exposures. below are some links you may want to read including one that will help you understand night photography better.

Answer 2

I would not use a neutral density filter for night photography, for photographing traffic trails. The purpose of these filters is to cut down on the amount of light reaching the lens and are normally used (a) if you have a very fast film in the camera and want to take longer exposures (b) to slow the shutter speed if, for example, you want to take those dreamy pictures of flowing water. I suppose you might use it at night to give you a really long exposure for traffic trails, but with a slowish film, I wouldn't have thought that necessary. If you do want to use one it will be in a circular mount that you screw to the front of your lens. Alternatively, if you have a square filter system like Cokin you just slip it into the mount.