Which is much better ?(Single or Multi-coating)

 The difference between single and multi-coating is not as great as that between an uncoated and a single-coated lens; the single layer of coating deals with the majority of the reflection, and multi-coating is a refinement to further improve its effectiveness. However, the difference becomes significant when there are a large number of reflective surfaces in the lens.

Multi-coating, as compared to single coating, represents a notable advancement in optical technology, particularly in the context of camera lenses and other optical systems.To understand the superiority of multi-coating over single-coating, it's essential to consider how each approach affects light transmission and image quality.

Single coating involves applying a single layer of anti-reflective coating to the lens surface. This coating is designed to reduce reflections and enhance light transmission. While it is an improvement over an uncoated lens, it still allows some light to be reflected, leading to potential issues with lens flare, ghosting, and reduced contrast. The effectiveness of a single coating largely depends on the quality of the coating material and the specific wavelengths it is designed to mitigate.

Multi-coating, on the other hand, takes this concept to the next level. It involves the application of multiple layers of anti-reflective coatings to the lens surfaces, each optimized to reduce reflections of specific wavelengths of light. The result is a lens that performs significantly better in various conditions, especially when dealing with complex optical elements, such as wide-angle and zoom lenses. The primary advantage of multi-coating is its ability to handle a larger number of reflective surfaces within the lens system.

In simpler terms, the difference between a single-coated and multi-coated lens is comparable to the contrast between an uncoated lens and a single-coated one. Single coating can significantly enhance the performance of a lens, but it does not eliminate all the reflective issues, while multi-coating aims to refine this further. This refinement becomes particularly significant when dealing with lenses that incorporate a multitude of optical elements, such as those found in complex wide-angle and zoom lenses.

To put this into perspective, consider a simple lens design like a Tessar, which might have a single-coated version and an uncoated one. The difference in image quality and performance between the two can be quite pronounced. However, when comparing a single-coated lens to its multi-coated equivalent, especially in a complex optical system like a zoom lens, the gap in performance becomes substantial.

It's important to note that not all multi-coating processes are created equal. Different manufacturers may use various methods and materials, leading to different degrees of effectiveness. The more layers of coating applied and the better the optimization for various wavelengths, the greater the performance improvement achieved. In other words, the quality of multi-coating can vary, and higher-end lenses tend to have more advanced and effective multi-coating.

In summary, multi-coating is significantly better than single-coating when it comes to improving the optical performance of lenses. While single coating is a substantial step forward from uncoated lenses, multi-coating takes that improvement even further, especially in complex lens designs. The more layers and the broader range of wavelengths a multi-coating process can handle, the better the results, with reduced reflections, lens flare, and ghosting, ultimately leading to superior image quality.