Filters

[DannyLewis]

I bought a 77mm UV filter off of ebay and recieved a CPL and an ND4 filter. What is the primary puspose of the ND4?
I did notify the seller he said keep them since I buy alot from him.

 

[SCraig]

Reduce exposure when there is too much light. Common use is when shooting flowing water in daylight and you need a slower shutter speed than you can get get. An ND filter is just neutrally dark and allows you to use a lower exposure.

 

[DannyLewis]

Thank you Sir

 

[CanonJim]

I bought a 77mm UV filter off of ebay and recieved a CPL and an ND4 filter. What is the primary puspose of the ND4? I did notify the seller he said keep them since I buy alot from him.

I'd toss the UV in a drawer and keep the CPL handy, if it's decent. DSLR sensors are not subject to UV light, so there is no scientific reason to use them, although some people like them for front element protection. But a clear filter will do just as well.

For outside, good light, landscape/nature type shots, however a CPL is highly recommended by almost all. Their effects can not be duplicated in post processing. You'll find that a good filter (e.g., one that doesn't totally foul up the light coming through it) will not be cheap - a good quality CPL will be $50 or more, and if you're really a drunken sailor, you can go the Singh-Ray route and spend $400+. B+W, Heliopan, Hoya, etc are good brands with decent products. Chances are, the $8.99 model you can get at Walmart will do more harm than good.

The ND4 filter is simply a dark piece of glass, as you've probably noted. It is used to reduce the amount of light coming into the lens during any specific time frame, so that you can take a longer exposure of a scene, and, as noted, get the "silky water" effect of movement by allowing a 1 or 2 second shot that would otherwise be wildly overexposed. Neutral Density filters come in various strengths, such as ND4, ND8, etc. Bigger numbers - darker glass.

A similar filter is a Graduated Neutral Density filter, or GND. This filter is darkish grey on one half, and then gradually lightens to clear by the middle of the filter or so. They are used to darken a very light area (such as the sky) so you can properly expose for a darker area below (like the foreground dirt and stuff). The dark half blocks out sky light. People who love sunset shots are usually looking through a GND, especially a sunset over water.

Almost every good landscape photographer worth his salt will carry a CPL, a GND and a few NDs, simply because their effects are difficult or impossible to create in Photoshop or whatever.