Grad. ND Filter vs. Polarizing Filter?

[Scbnymph]

Hello everyone. I'm a very amateur photographer and have been trying to figure out the answer to my question but am having difficulty. Basically, what is the difference between a ND filter / polarizing filter, and when should I choose one over the other? Should I ever use them together?

What I've read so far makes it sound like they do almost the same thing but in different ways, and I think that's whats confusing me. I'm obviously missing something in my understanding and so I turn to you for help.

Thank you.

[RichardTaylor]

A ND filter darkens all or part (graduated ND) of a scene.

That is the only thing it does.

A ND filter is used for more control over exposure or (Graduated ND) to reduce the apparent contrast of a scene.

See this post.
Neutral Density Filters

and this may be of interest.
Introduction to Filters for DSLRs



A polariser may darken part of the a sky (depending on the light and the angle it is to the camera) and possibly reduce reflections.

See this post
How to Use and Buy Polarizing Filters

[Doug Sundseth]

So, first, you're talking about three different types of filters, not two: an ND filter is not the same as a graduated ND filter.

A polarizing filter only allows the component of light polarized in the same direction as the filter through. Light is usually polarized by reflection, most commonly off of the surface of water or off of particles in the air. These filters are used to preferentially reduce the intensity of reflected light, which can help the appearance of the surface of water or deepen the blue of the sky.

A graduated neutral density filter as one part that is clear and one part that reduces the transmission of light by some amount (2 to 4 stops is common, or 75% to 94% of the total incident light). These are commonly used when the dynamic range (the range between brightest highlight and deepest shadow in the frame) of the photo is too great to be captured by a camera's sensor. You have to place the edge of the filter where you want the light reduction to start, and if the horizon is complex the results can be suboptimal. For most purposes, as soft edged filter is what you want.

A neutral density filter has a single density across its width. It is used to get longer exposures or wider apertures in bright light, for instance to get a nicely blurred background in a sunlit scene or to blur a waterfall in daylight.

HTH

[Scbnymph]

Thank you both for your replies.

@Richard. When I was searching, your Intro to Filters link didn't show in my results for some reason, so thank you for posting it as it helped my understanding. I'm now tempted to go buy a UV filter...

@Doug. Thank you for the explanations, they're the most understandable (for me) that I've read thus far. Confusing the graduated and regular ND filters might be part of my problem.

I currently have a CPL that I tend to keep attached to my lens most of the time because I like the way that it makes my colours more vibrant. Should I be more selective of when I use it? For example, yesterday I took a photograph outside with a rainy, very cloudy sky, would it have been better to not use the polarizing filter? Would I have been better off using a neutral density filter instead? Re-reading both your posts maybe a UV filter would have worked well?

[Doug Sundseth]

The cover over the sensor on your camera does all the UV filtration that is necessary. Putting a separate UV filter over your glass doesn't do anything but degrade image quality.

A polarizer eats about 1-1/2 stops of light, plus it's another piece of glass in front of your expensive lenses. You don't want to just keep it on by default. Plus it's yet another thing to fiddle with when you are (I am ) trying to get the shot I'm looking for.

Many shots do not need any filters at all. I would recommend only using the filter or filters that you need for a specific effect, and only when you need that effect.

[RichardTaylor]

+1 Doug Sundseth's suggestion.

The only time you may want to consider a UV filter is when shooting in inhospitable or dirty environments.