The type of glass used for the lenses of any optical instrument has a bearing on the quality of the image that you can see through it. When you use binoculars you need them to transmit the light through the body of the binoculars in order to see the image.
For binoculars, it is best to use specialized glass, rather than the generic kind of optical glass. If there are imperfections in the lenses, due to the way the glass has been ground and polished, then these imperfections will show up in the form of distortion or aberration in the images.
What is Eco glass?
Eco glass is made without the potentially harmful chemical elements arsenic and lead. It is ecologically friendly glass because when its useful life is over and it needs to be thrown away, it will not be contributing to chemical pollution.
What is the prism in binoculars made of?
Glass is used for several components in the construction of binoculars. Different kinds of glass are required for the lenses and for the prisms inside the binoculars.
Learn more about the function of the prisms in binoculars here.
What type of glass is used in optical instruments?
There are many ways of formulating glass to meet different functions. Each formulation has unique properties. Thus, every formulation has its own designation.
Crown glass is a kind of optical glass. There are two designations of crown glass that are commonly used in the manufacture of optical instruments, such as binoculars and scopes.
What glass is used for prisms in binoculars?
These several types of crown glass are used to make the prisms inside the optics:
Both types take their name from an element used to modify the composition of the glass.
What does BaK-4 mean?
Ba is barium. BaK-4 is a light barium crown glass.
More specifically, BaK-4 can be made of barium or phosphate crown glass. The barium is better than phosphate crown, but this is rarely listed in specs.
A manufacturer should be able to give you more information if you require it, though.
What does BK-7 mean?
B is boron.
BK-7 (as well as the very similar K9) is a type of borosilicate crown glass.
What is K9 glass?
K9 is another kind of borosilicate crown glass, like BK-7, used in the manufacture of optical products.
The ‘K’ stands for the word ‘krone’, which means ‘crown’ in German.
What is the difference between BaK-4, BK-7 and K9 glass?
Both BK-7 and K9 cost less to produce than BaK-4. They are therefore found in lower priced products.
BK-7 and BaK-4 are the kinds of glass that you will see most commonly used in binoculars and scopes.
The best prism glass: BAK4 or BK7?
Using binoculars with BAK4 is recommended. It is worth the upgrade for the better quality of the prism glass. When you examine the specs of the higher end binoculars, you will notice that they always use BAK4 for the prisms.
Another advantage of choosing a binocular with BAK4 is that it is possible to get it with ED glass.
LINK – what is ED glass and why is it important?
BK-7 glass prism v BaK-4 glass prism: which is best?
Before we look in more detail at the advantages and disadvantages, let’s get a quick overview:
Pros of BK-7 Glass
Acceptable image quality
Scores 1.52 on the refractive index
Cons of BK-7 Glass
Does not match BaK-4 quality
Pros of BAK-4 Glass
Top image quality
Scores 1.52 on the refractive index
Available with ED glass
Some lower cost options possible
Cons of BAK-4 Glass
Binocular prisms: what is the best glass?
BaK-4 is the better and more expensive prism. Any binocular that features BaK-4 prisms will probably say so in their spec.
If the prism glass is not specified, then it is probably BK-7 or K9 glass.
Why is BaK-4 glass recommended?
One of the important properties of BaK-4 glass is its high refractive index. The refractive index indicates how effectively a glass transmits light.
This means BaK-4 is exceptional at transmitting a higher quantity of light, with a lower amount being lost to internal reflection due to imperfections.
Light transmission is the primary function of the prism inside binoculars. Therefore a prism assembly using BaK-4 glass delivers the best image quality than one that uses another kind of glass.
Prisms made of BaK-4 glass are therefore considered as the best type.
Are BAK4 binoculars worth it?
The BAK4 prism is crystal clear. You can see the difference in the vibrancy of the colors.
They cost more but there are still affordable models available.
Are BK7 binoculars any good?
BK7 is a type of optical glass commonly employed in the construction of binoculars. It is used for its properties of light transmission. The number of imperfections in BK7 glass is low.
Image quality is better with BAK4 than with BK7. If you are on a very tight budget and BK7 are the only option for you, then the preferable choice is a smaller magnification and an exit pupil of at least 4mm.
LINK – What is exit pupil and why is it important?
In binoculars up to 8x power, the field of view is wider. The image quality with BK-7 will be better with a wider field of view.
It is definitely possible to find top quality binoculars that do use BK7 prisms. Hopefully by being thoroughly informed about the differences, you are more equipped to make the best choice for you.
How can I tell the difference between BK-7 and BaK-4 glass?
You can look at your pair of binoculars to get an idea of whether the prisms are made of BK-7 or BaK-4.
(The following can be a helpful guide, but to be completely sure of the kind of glass, check the product specification.)
Hold the binoculars with the objective lenses facing you – the opposite way around to usual – and a little bit away from your eyes, around 6 to 8 inches.
Look into the objective lenses at the exit pupil. The exit pupil is a bright rounded shape.
With Bak-4 prisms this shape should be more perfectly circular.
With BK-7 prisms some of the edges will appear more squared off.
This demonstrates how BaK-4 prisms have superior light gathering and transmission, because they capture a sharper image the whole way across, with no loss of brightness at the edges.
What is SK15 glass?
SK15 is another type of optical glass that you may see listed on specifications.
While it scores more highly than BaK-4 and BK-7 on the refractive index, its dispersion rate is between BaK-4 and BK-7. In essence, the light transmission is well directed, with a minimum of internal reflections.
This means that binoculars using prisms made of SK15 glass offer images of excellent clarity and contrast. In this sense, it is a good compromise between the two types of glass previously mentioned.
What do I need to know next about glass in binoculars?
Bird watching experts consider that BaK-4 glass delivers the best image quality in binoculars. When BaK-4 glass is used for the prisms within binoculars, it is excellent at reflecting the light with the lowest number of imperfections.
It is also worth knowing about the benefits of extra-low dispersion glass, and high-definition glass, which we cover in this article.
- 1 What is the prism in binoculars made of?
- 2 What glass is used for prisms in binoculars?
- 3 The best prism glass: BAK4 or BK7?
- 4 Binocular prisms: what is the best glass?
- 5 What do I need to know next about glass in binoculars?