1. Mounting systems.
The basic filter accessory mounting systems:
Depending on the model a circular polarizer is compatible with the slotted holder. It can be rotated within the holder allowing for colour saturation adjustment.
2. Filter sizes.
A circular screw in filter must be the same diameter size as your lens; look for the symbol O with a line through it, on your lens.
Look for numbers such as 52 (mm), 62, 72 – check on the front of the glass, the lens cap or on the lens body to find these numbers. They are the size of your lens in mm.
3. More than one lens.
You do not necessarily need filters for each of your lenses which are a different size.
You can buy adapter rings which will let you mix and match different sizes.
For example: you could use a 72mm filter with an adapter ring fitting a 67mm lens instead of buying both a 67mm and 72mm filter.
4. Common filters.
With a polarizer you will not see any change in light with overcast, mist or fog, nor if the sun is directly in front of you or behind you.
The best angle to the sun is at a right angle to the direction you’re pointing your camera.
A circular polarizer will change the light and saturation, which you can see as you rotate it in the holder.
Both of these filters will reduce a certain amount of light, and depending upon the type of neutral density filter it may be minimal or quite substantial.
Vignetting occurs when an obstruction on the front of the lens blocks some of the light, such as a lens hood or a filter(s) obstruction.
This is revealed by a dark area(s) around the edge of your images. If this happens double check the placement of anything which may be obstructing the front of the lens enough to cause vignetting.
6. Protecting the lens.
A controversial topic is whether to use a commonly recommended sky light filter to protect the lens glass, and the end of the lens.
Debate for: it helps protect the lens from damage such as scratches, dirt, dust and accidental drops and bangs.
Debate against: if you’re paying good money for good quality glass in your lens why would you want to cover it up with a filter, which can affect the quality of your photographs?
My suggestion is to go with what you feel comfortable with.
I have witnessed lenses being saved by them as well as deterioration in image quality.
Personally, I may keep a filter on a lens when I’m not using it and take it off for the photo shoot.
It also depends upon the conditions:
If there’s dust and grit in the air or the potential for it to come my way, or wind and rain I may very well decide to use one.