Organizzoranzi: Cosa sono i filtri Multi-Coated e a cosa servono

da http://www.2filter.com/faq/multicoatedfaq.html

The Filter Connection www.2filter.com
Multi-Coated Filters, are they worth it?

Is your current filter, Multi-Coated or even Mono-Coated?

Here is a very simple way to check.
Look at the reflection of a lamplight bulb, at an angle, on the surface of the filter (UV's or Sky's are the best to use). Filters that have optical coatings, multi or mono-coated, will reflect white light, when viewed from an angle, at a tint, slightly different than white.

Multi-coated filters will reflect the image in many different colors (usually magenta and green tones), depending on the number of optical coatings applied to the surface of the glass, just like most camera lenses. Mono-coated filters will also show a tint change, but the tint is harder to see. Non-coated will show no tint change, of the bulb. To compare the reflections, with glass that is known not to be coated. use regular glass, from a photo frame.

Don't be surprised if your filters do not have any coatings at all. Many well known filter brands do not have optical coatings.

Stop defeating the fine coatings on your lenses with filters without any optical coatings. MULTI-COATED FILTERS are available now from all major filter companies. You will see a difference, especially if you shoot without a lens hood outdoors or with a wide-angle zoom with a shallow hood.

The above image was created in 1989 and is property of 2filter.com

Today's lenses from all the camera companies -- normals, zooms, telephotos and wide's are all multi-coated. Multi-coating helps reduce most surface reflections. We feel this is an important function, allowing maximum light transmission. However, this multi-coat benefit is only secondary to the reduction of flare (reflection).

The problem of natural lens flare is encountered from any stray light entering the optical path from angles not necessary to capture the required image on film. Lens flare is most noticed when you are taking images with strong back light situations, example Sunsets, scenic's, studio portraits, fashion etc. Using hoods as deep as possible for the working focal length in use is a big step in reducing the light flare problem. Today's zooms have such a wide range. The hoods supplied with lenses are usually very shallow - to cover 28 to ??? (200mm focal length).

The reflections of light happen at every air space between lenses and filter elements. Internal lens reflections are usually at an extreme minimum because the light becomes focused as it passes through the lens elements.

The rear coating of the filter (the part that faces the lens) is the most critical surface to be coated. If the filter rear surface is multi-coated, it will reflect the minimum amount of light back to the first element in the lens group.