Anti-Reflection Lens Coatings
In optics, anti-reflection lens coatings are included in design specifications to improve light transmission, producing a brighter image with more contrast. Almost all high quality optics have some sort of anti-reflective coating applied to at least one air-to-glass surface of the lenses.
Anti-reflection coatings usually consist of a number of very thin transparent film layers, each having a distinct index of refraction to alter the lens performance with different wavelengths and at different angles of incidence. Sometimes, you can see these coatings by looking for blue, red, or green reflections as you look into the front of an optic’s objective lens at different angles.
Improved Light Transmittance
Some of the light passing through the lens is always reflected by the front (incident light) and rear (exiting light) surfaces. This reflection restricts the amount of light that can pass through the lens to your eyes, making the image darker. This can also cause ghosting, flares, and detract from the contrast of the image.
Because of this, anti-reflective coatings are added to the lenses of better quality optics, decreasing the amount of lost surface light and greatly increasing the light transmittance. This gives you an image that is as bright, clear, and sharp as possible.
Coated vs. Multi-Coated vs. Fully Multi-Coated
You should pay careful attention to how a manufacturer describes the coatings on an optic you are considering for purchase.
- Coated: A single layer of anti-reflective coating is applied to some, but not necessarily all, lens elements. Usually, this is applied to the first and last elements, the only ones you can see.
- Fully Coated: This means that all air-to-glass surfaces are coated, an improvement over a single layer of coating.
- Multi-Coated: When an optic is described as multi-coated, this means that at least some surfaces (once again, usually the first and the last) have multiple layers of anti-reflective coating. This increases the transmittance of light, because it reduces the amount of reflected light that cannot be eliminated with a single layer of coating. Multiple layers are an order of magnitude better than a single layer.
- Fully Multi-Coated: With optics that are fully multi-coated, all air-to-glass surfaces are treated with multiple layers of anti-reflective coating. This provides the best possible light transmittance.
How Much Does It Cost to Make Fully Multi-Coated Optics?
In days long past, you’d only find fully multi-coated optics at the highest end of the market. Nowadays, however, production methods have improved and gotten cheaper, largely due to the influence of cheaper production costs from Asian manufacturers, so more and more optics are being fully multi-coated.
The moral of the story is this: more and more low cost optics now come fully multi-coated, so this is what you should look for regardless of your budget.