Lens Filters
I’ve got a couple types of filters and I always keep a UV filter on my lens because it protects the lens from dust, moisture and gives an added layer of protection to expensive lens replacement. Last fall I dropped my camera onto a concrete floor (waist height) and when I picked it up… the glass was shattered. I was afraid my $1200 lens was ruined, but luckily, the UV filter was the only damage. The impact shattered the glass and bent the brass housing. Removing the broken filter was very difficult because filter wouldn’t unscrew

UV (Ultra Violet) Filter
I don’t think it makes a world of difference on UV filters, as far as performance goes. I originally bought a $100 B+W UV filter, broke it, and replaced it with a $50 B+W UV filter. I couldn’t tell any difference (other than price). If I had to replace another one, I’d probably get a Canon UV filter, which is even cheaper.

Polarizing Filter
This is a great item to have for outdoor shots. The filter eliminates most of the reflective light. If you shoot a car, normally the windshield looks white (reflective light) – but the polarizing filter eliminates this. Anytime you shoot a body of water, the filter helps get rid of the glare.
This filter also helps when I didn’t expect it. If you shoot 90 degrees from the sun, it eliminates reflective light in the atmosphere (light bouncing off moisture in the sky). The end result is a true blue sky and much better color. If you’ve ever seen photos of beautiful white clouds in a deep blue sky, this filter is the reason. Another great place to use the filter is in snowy conditions. Colors really come out. Without a doubt, this is my favorite lens filter.

My lens cap will not fit this filter, so you may have to buy it separate (if they offer one). I have a B+W polarizing filter. Heliopan filters are also top of line.

Neutral Density Filter
They also make a neutral density or split polarizing filter, which allows you to filter the sky and leave the earth alone. This would be useful if you wanted to have less contrast in a shot which shows a field and sky. The filter darkens the bright sky & leaves the (already dark) field alone. You’ve probably noticed sometimes the sky is so bright that your camera tries adjusting the white balance… and the field is underexposed (too dark). I don’t have this filter, yet.

Other Filters
There are many other filters. Warming filters which add color. Softening filters which make an image glow… etc – Most of these effects can be added later in Photoshop, with the ability to increase or decrease the effect.

Filter tightening
It’s stuck. The first time your filter sticks to your lens, you get a bad feeling. It seems no matter how hard you try, it isn’t coming off. I’ve tried a lot of different things and don’t remember anything that really seemed to work except just fiddling with it.
I’ve tried the refrigerator, canning jar mitt, tapping the threads with something hard and I’ve even got out a large wrench. (Thank goodness it wouldn’t open that wide!)
I have no idea why but several times I’ve laid the lens down and came back later to give it a try. It unscrews without any effort!
Sometimes after struggling for a few minutes and on the verge of sweating, I’ll try putting a small amount of pressure on the filter and just barely turn it. Off she comes. It may take 37 tries!

Filter installation
Clean your lens and filter to perfection (canned air and brush). I like using daylight, so I can detect small fibers or dirt). To keep my filter from binding to the lens or another filter, I have a method which seems to work. I screw the filter on slowly (clockwise). Finally I can feel the filter stop turning; stop turning. It’s not tight because I was turning slowly.
Now I will back the filter up (turning counter-clockwise) one billionth of an inch. In other words unscrew it just a hair, a tad, a bit anything to get it away from the tight spot.
I think that leaving it too close to the tight spot could cause accidental filter seizure (filter getting stuck).
Here’s why: If the filter is against the tight spot and your equipment knocks up against a tree, at the wrong angle, it may cause the filter threads to screw into the lens. Just enough to cause the filter seize. Remember, it doesn’t take much.
The downside is that the filter could eventually work itself off (unscrew). So I have a habit of testing the tightness and backing it off, several times per shoot.

Installing a filter on a filter
When I want to use the polarizing filter, I have to screw it into the UV filter. For some reason they are even worse about seizing (getting stuck). I take the same precautions as above. As I’ve said, the polarizing filter won’t accept my lens cover, so I walk around with the polarizing filter mounted. On several occasions the polarizing filter has fell off (unscrewed itself). They must be made pretty well because they have hit rock surfaces from waist level without any damage!
I believe the filter unscrews easier (hitting my leg as I walk), without a lens cap.