Hexalite, a couple of points to add to what Frank has already said.
The HD designation is by and large a marketing term which trades on the hoopla surrounding the 720p, and 1080p standards for display devices (like TV's). However, it can also be used to indicate 'High Density' glass, which is meant to offer improved performance.
I don't think there's any water-tight agreement within the industry on it's usage, so it can mean anything from 'pure marketing fluff', to 'higher quality / transmitting glass', to 'low, or even extra-low dispersion glass', and probably anything in-between. Not all 'HD' glass is ED glass.
To add to the complexity, not all ED glass is created equal - there are several grades. The better grades of ED glass cost more - there are no free lunches in binoworld! ED glass is used to minimise CA (Chromatic Abberation) - basically the colours don't all line up to where their supposed to, causing colour fringing of various colours and severity. This affects each individual differently, and some people are not bothered by it at all.
Dielectric roof prism coatings offer around 99% reflectivity, versus around 90%+ for the other types. You should note that a porro prism (those old military style, looking binoculars) offer 100% reflectivity, since it's all done with internal geometry and negligible losses - there are many fans of porros, especially at these lower price points, to give more brightness bang for the buck - just make sure they are modern production designs, with the latest fully multi-coated lenses.
The losses on the prisms, add to the losses on the other lenses, to give the overall transmission ratio (generally ~85% for budget stuff -> 95% on the best $2k+ 'alpha' stuff). There is some debate around here as to how much additional brightness can be detected by the human eye - some feel its 3%, some 6%, or more.
The other consideration is age - if younger, you'll gain much benefit from the 8x42 size. It's easier to use, brighter, and you'll see more stuff, more of the time.
I, like many here, like brightness (dielectrics, or porro) AND minimised CA (ED glass). eg. Zen-Ray 8x43 ED3, roughly double your budget. You could spend well over $2k on relatively, marginally better than that 'alpha' bins - the law of diminishing returns. You have to choose what looks best for you. Good luck!
Chosun :gh:
For more information, please visit Optical Coatings.
Welcome to Optics Trade debates. In each episode, we talk about a different topic and try to answer the most common questions we receive about it. Today, we are going to talk about lens coatings.
In the past, manufacturers produced lenses and prisms out of normal glass. There is a lot of light lost when traveling through the optical construction of optics that pre-date WW2 (they lost from 30 to 50% of light).
Zeiss noticed that coating the surface of the lenses with a special material minimizes the loss of light. With that revelation, they improved the light transmission rate from 50% to 80%. When lens coatings started to be used, terms like relative brightness and twilight factor became irrelevant because of the change in optical properties.
Coated optics have some lens surfaces coated. Only some are covered and with only one layer of material.
Fully coated optics have all surfaces coated on all lenses and prisms. They are covered with one layer of material.
Multi-coated optics have multiple layers of different materials to achieve a better light transmission rate. There can be more than 20 different layers on some glass elements.
Fully multi-coated optics have multiple layers of different materials on all lenses and prisms. This is more or less becoming a standard.
The best optics on the market have 96-97% light transmission rates, which is astonishing when compared to optics that were made 50-70 years ago.
There are three types of coatings.
There are the coatings that are used on glass elements with an intention of improving light transmission rates, resolution, color fidelity and achieving superior optical performances.
There are coatings that prevent external fogging when the optics are in use in lower temperatures. These are coatings like AquaDura, LotuTec, RainGuard… These coatings are hydrophobic.
If you are looking for more details, kindly visit Fused Silica Mirror with a hole.
The third type of coatings prevents scratching on the objective lens. Some coatings combine the function of this type and the fog-proof type.
The majority of optics that cost more than 200 € have fully multi-coated lenses and prisms.
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Explanation of the term on our website:
Optical products have many lenses in their housing. With each lens, about 5% of the light passing through is lost. This can be solved with an application of coatings on the glass surfaces. With years the technology of coatings changed. At first, they used only one layer, where the reduction of the loss was to 2% per surface. Today they use multiple layers of coatings where there’s minimal loss of light – 0.1% per surface. The best binoculars have even 95% of the light transmitted to the eye, through all their lenses.
With increasing transmission of the light, the coating is also important as a protectant of the optical glass and to ensure the true color fidelity, so the colors when entering are the same when exiting binoculars/riflescope. Above all, coatings also increase the image quality because all the light bouncing around on the inside can cover up detail and blur colors.
The process of applying coatings has to be precise, otherwise, it can contribute to a hazy and blurred image. They must be spread evenly and thinly to ensure the best quality. The better the coatings, the more expensive the optical product.
Lens coatings are as important as the quality of the lenses themselves. You can easily check whether your optical product has coatings – if you look at the reflection and it shows multiple colors such as purple, green or yellow the lenses are definitely coated. On the opposite, lenses with no coatings have a clear reflection without showing any colors.
There are many different ways of applying lens coatings:
Coated: where one or more glass surfaces are coated with one thin anti-reflective layer.
Outer surface coating: coating on the outer glass surface which protects the lens from external dew (especially in the winter), partially from dirt and other impurities. They can have different names, depending on the manufacturer (LotuTec, Swarodur, AquaDura)
Source: ZEISS
Products mentioned:
Binoculars: https://www.optics-trade.eu/en/binoculars.html
Riflescopes: https://www.optics-trade.eu/en/riflescopes.html
Spotting scopes: https://www.optics-trade.eu/en/spotting-scopes.html
NV optics: https://www.optics-trade.eu/en/night-vision-optics.html
If you want to learn more, please visit our website quality achromatic doublet lenses.