BAK-4 vs BK-7 Prism – Which is Best?
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Many people have binoculars but not all of them actually know the difference between BAK-4 and BK-7 prism. Though there is a difference.
If you don’t know anything about this type of prisms keep reading and I believe you will learn something new from this short post.
It’s generally accepted fact that BAK-4 prism is superior to BK-7 prism. I had a chance to test BK-7 prism binoculars and they are not bad.
But once you see the difference between BK-7 and BAK-4 you will no longer want BK-7.
Prisms are made of a glass and depending on the type of glass the image produced by binocular can be either sharp, clear, and bright or vice versa.
This doesn’t mean binoculars made of BK-7 prisms are not usable or produce a bad image. It’s just significantly different from BAK-4 quality.
BAK-4 quality is a lot better. BAK-4 prisms are made of the material of higher quality than BK-7.
They allow to transmit more light and we getter better and brighter image as a result.
Some optical devices are made of ED or Eco Glass material which is even better than a standard BAK-4.
It means extra-low dispersion glass which allows to get even brighter image without aberrations.
If you look at the screenshot below you will notice that BK-7 has a clear image only in the center of an exit pupil and looks like a squarish image.
Especially such an image is visible when manufacture uses prisms of a small size. Image is less bright than in BAK-4.
For many people it may not be an issue especially if you are on a tight budget. But for those who understands optics this may be a problem.
I personally love BAK-4 or ED Glass.
I never use BK-7 other than for testing purposes. BAK-4 glass is more expensive material than BK-7 and that’s why image quality is WAY better than in BK-7.
Should you buy or avoid BK-7 prism binoculars?
From the said above it becomes clear than BK-7 can’t beat quality of BAK-4 prism.
If you choose binoculars with magnification up to 8x then BK-7 still can be acceptable. Because magnification up to 8x has a wide field of view.
When magnification increases field of view becomes narrower. This means in how power binoculars with BK-7 prism image quality may not be acceptable at all.
This means if you are on a tight budget and plan to buy BK-7 binocular choose one with a small magnification, preferably up to 8x and exit pupil should be at least 4mm.
Generally speaking I recommend to buy BK-7 prism binoculars only if you are on a tight budget.
Pros of BAK-4 Glass
- High quality image
- Budget binoculars available
- Refractive index rate 1.57
Cons of BAK-4 Glass
- Some binoculars may cost as much as $2,000
Pros of BK-7 Glass
- Cheap binoculars available
- Image quality is acceptable
- Refractive index rate 1.52
Cons of BK-7 Glass
Image quality is not as good as BAK-4
Tip 1: BAK-4 prism non-branded binoculars manufactured in China may be inferior to branded BAK-4 binoculars. But still it’s much better than BK-7 binoculars.
Tip 2: Not all BAK-4 binoculars are of the same quality. BAK-4 glass is made of either Barium or phosphate crown glass. Barium glass is superior to phosphate crown. If this info is important or critical for you then contact manufacturer directly.
BAK-4 vs BK-7 – Which is the best?
Of course, BAK-4 is much better than BK-7. BK-7 can’t beat the quality of BAK-4 glass.
If you a budget to spend you can always choose BAK-4 prism binocular with ED Glass. This means higher quality image, brighter and with zero aberrations.
You can get such a pair of binoculars even for $100.
When it comes to BK-7 glass you will never find BK-7 with ED glass. Such binoculars simply don’t exist.
Unless you are on a tight budget I highly recommend to always choose BAK-4 binoculars.
Fortunately, there are different models available on the market.
You can buy quality BAK-4 binoculars even for less than $50 and the image quality will be more than acceptable.
Glass quality is not the only factor that affects image quality produced by binoculars. Lens coatings do matter as well as prism size.
If all this done by a branded manufacture of optics on a high level, such as Nikon, Bushnell, Wingspan or any other then BK-7 prism binoculars can produce acceptable image quality.
Otherwise you better spend extra $20, $30 and get BAK-4 binocular.
BAK-4 affordable binoculars
Compact Binoculars for Adults/Kids, 10×25 HD Roof Prism Folding Binoculars
– Wide field of view
– Magnification power 10x
– BaK4 prism
– Customer satisfaction: 97%
– Price: $21.99
Binoculars for Adults Compact and High Powered – 10×25
– Wide field of view
– Magnification power 10x
– BaK-4 prism
– 97% Customer satisfaction
– Price: $30.97
Whew 10×42 Roof Prism Binoculars for Adults
– Wide field of view
– Magnification power 10x
– Prism type: BAK4
– 100% Customer satisfaction
– Price: $40.99
12×42 Roof Prism Binoculars for Adults
– Bak4 Prism
– Magnification power 12
– Customer satisfaction: 94%
– Price: $37.96
BK-7 acceptable binoculars
Celestron 71198 Cometron 7×50 Binoculars
– Wide field of view
– Magnification power 7x
– BK-7 porro prism
– 85% customer satisfaction
– Price: $33.98
Bushnell Powerview Falcon 10×50 Wide Angle Binoculars
– Wide field of view
– Magnification power 10x
– BK-7 prism
– 73% Customer satisfaction
– Price: $54.94
Bushnell Falcon 133410 Binoculars 7×35
– Wide field of view
– Magnification power 7x
– BK-7 porro prism
– 87% customer satisfaction
– Price: $28.98
Mini Compact Lightweight 8×21 Small Binoculars
– Wide field of view
– Magnification power 8x
– BK-7 prism
– Customer satisfaction: 85%
– Price: $9.79
Bushnell Powerview Compact Folding Roof Prism Binocular 8×21
– Wide field of view
– Magnification power 8x
– BK-7 prism
– Customer satisfaction: 75%
– Price: $11.99
About the Author: Adam
We review and recommend quality binoculars so you don't waste your money on useless ones. 
As a physics student, I know a lense or glass with high refractive index produce a clearer image compare to the ones with low refractive index. I used to have BK 7 binocular when I was in college. You know how it means when you are the only one opportune to have something very important among your clique. We use it to view anything we want . Wow, technology is not static, so we have more advance materials. Am glad I come across different kind of BK 4 binocular here. Only that some are not pocket friendly but I’ll still see friends interested in them. When my kid reach age 7, I wish to get one for him.
Good to know you have BK-7 binocular. BTW, BAK-4 prism binoculars are not new. They have been used for years now. BUT ED glass ones are new. They deliver better image with the least chromatic aberration. If you need to choose a good pair of binoculars for your son let me know and I will be happy to help you with your choice.