This is the construction of a type of filter. The type of process used to create a filter can affect its price. Filters can be constructed out of regular glass that sandwiches a coloured gel in between or in high-end filters, raw elements are added to the molten optical glass so there is no risk of uneven colour or fading.
UV: Reduces excessive blue; cuts through haze and can improve image clarity; protects front element of lens; Circular Polarizer: Removes reflections and increases color saturation without affecting the overall color balance; Neutral Density: ND filters appear gray and reduce the amount of light reaching the film, they have no affect on color balance
Allows various filter effects to be done in-camera while shooting. Common filter effects are vivid, neutral, sepia, black and white, negative, cooling, warming, etc...
This is the size of a front lens cap. Standard sizes for snap-on lens caps include: 27mm, 28mm, 30mm, 34mm, 37mm, 39mm, 40.5mm, 43mm, 46mm, 49mm, 52mm, 55mm, 58mm, 62mm, 67mm, 72mm, 77mm, 82mm and 86mm.
UV: Not Applicable; Circular Polarizer: Between 2.3 and 2.8 (approx. +1.3 stops); Neutral Density: Reduces ISO to 1/8
When placed in the optical path, many filters block a certain amount of light from reaching the lens. Filter factor relates to how much exposure compensation is required in order to adjust for this. Most cameras have TTL metering and will be able to do this automatically.