HOW FILTER WORK

UV / PROTECTION FILTERS

A UV and Protection filters' main purpose is to protect the front part of the lens from dust, dirt, liquid, and scratches. It can also help improve contrast and detail at high altitudes by reducing UV Haze. This article will help you understand how the filter works and learn about what features are important when buying a good quality filter.

TOP 5 REASONS TO OWN A UV FILTER

Protect the front of your lens from dust and dirt
Protect the front of your lens from water and scratches
Protect the front of your lens from oils and smudges
Blocks contrast killing haze at high altitudes when using modern digital cameras
Blocks that same haze at all altitudes when using film cameras

KEY FEATURES TO LOOK FOR WHEN BUYING A UV FILTER:

Photo by : Hoya Filter USA

The Glass:

All filter glass are not created equal and poor quality glass can affect sharpness, resolution, contrast and color. Inexpensive filters will use simple window glass, polish it, throw it in a frame and call it a day. Where the highest quality filters will use optical grade glass to ensure you see no difference in image quality from the unfiltered lens.

Optical Glass is best and is more expensive. Hoya also takes it one step further and produces an exclusive optical glass that is chemically hardened to make it 4x harder that other optical glass.
Schott B270 glass is not optical but it is as close as you can get without being classified "optical". This makes it a very popular base glass for many legit filter companies.
Look for terms like "Water White" and "Hoya Clear". This glass is not optical but still a very high quality glass that will serve as a great protection filter
Avoid any filter that does not clearly state what type of glass it is. More often than not the filter is simple window sheet glass with lots of impurities in the glass that ruin image quality.
And, look for glass that is "Black Rimmed". This means the manufacture took extra care to paint a black rim on the outside edge of the glass. This ensures light does not bounce around and off the surface of the filter frame.

Multi-Coating Layers

Photo by : Hoya Filter USA

Good quality multi-coatings, properly applied during manufacturing will increase the light transmission of the filter (more light passes through the glass) and reduce or eliminate reflections on the front and rear of the filter. More layers usually means better light transmission, but more also means increased cost.

All High quality UV filters will have multi-coatings on both sides of the glass. Make sure the specs state that both sides are coated.
More layers means better light transmission but comes at an increased cost.
Light transmission 98% or higher is very good and is enough for most photographers
Multi-coatings prevent double image reflections or ghosting, contrast reducing flare, and increase color accuracy.
Avoid non-coated or mono-coated UV and protection filters. You will not be happy with the results.

Premium Coatings

As part of the multi-coating process manufactures will add premium coatings to enhance the function and durability of the filter. They are great features that also come with an increased cost. Filters will use none, some, or all of these features which include:

Waterproofing that helps liquids bead-up on the surface of the glass and easily roll off or wipe clean.
Scratch Resistant to prevent incidental damage to the surface of the filter.
Oil and Smudge resistance makes it a lot easier to wipe your filters clean when a finger print or dirt is on the surface.
An Antistatic layer is used to prevent the generation of a static electric charge that occurs when rubbing the surface of the glass during cleaning, keeping dust from sticking to the surface.

The Filter Frame

The frame is the outside ring that the filter sits in and allows you to screw it onto your lens. Frames are usually made from Brass or Aluminum. In our experience we find there is no particular advantage or disadvantage to either and both are a good material for the frame. Most filter frames come in 2 pieces; the base frame that the glass filter is dropped into and then a retaining ring that clips or screws in to hold the filter in place. This is the way most filters are assembled and is usually not a problem unless the retaining ring loosens or spins out completely. For this reason Hoya also uses a process called Press Fit.

Press Fit

A Press Fit filter frame is a single piece of aluminum (brass is to hard of metal to do this) that is expanded in a special press just enough to drop in the glass filter then released to create a solid single connection around the entire filter. This ensures the filter will stay in place and more importantly remains completely parallel to the camera's sensor plane when installed correctly onto the lens.

Frame Thickness

The thickness of the frame matters if you are using extreme wide-angle lenses 20mm or wider on a full-frame camera. Thin mount frames prevent the lens from seeing the actual filter frame in the image, also call vignetting. If you are using these types of lenses look for filters that claim to be "thin frame" or low-profile" frames.

source : https://hoyafilterusa.com/pages/uv-filters