Neutral Density vs Grey ? I am confused

[emalf]

What is the different between a neutral density filter and a grey filter ? They seems doing the same thing. I am confused about this. What about graduated neutral denstiy and graduated grey? What is difference?

Currently I only know that the grey filter is cheaper, which suggest they are different. But how they from each other, anyone know?

Thanks.

[palmbook]

grey filter leaves grey tint on your final image.

go for ND if you have enough money.

[emalf]

Then what about graduated? It seems there is no graduated neutral density filter but only graduated gray. I can only find half neutral density filter but not graduated.

According to the physics I had learn, grey is a composition of RGB. Then the gray filter should filter both RGB light. It becomes what the neutral density do, reduceing the amount of light. I said these because most censor CCD and CMOS detect RGB only. Am I right?

[palmbook]

When you wear sunglasses, you can see the world is dimmer and somewhat unsaturated. Cheap sunglasses work the way grey filter works - lessen the light transmitted through. The side-effect is it leaves grey tint, as you can see through the glass.

ND is designed to solve this problem. Although it serves the same purpose, ND doesn't leave any color cast nor any reduction in saturation. This's why ND is (a lot) more expensive than grey filter.

There is ND-grad. This filter is a magic bullet for a landscape photographer. However, most of ND grad-filters are square filters, becuase of necessity of moving the filter up and down (your skyline doesn't have to be exactly centerized. So, you need a filter that can move according to skyline).

The round-filters are also available. I bought one and sold it already. It's Tiffen. I sold because I prefer to bracket the exposure and combine details later.