BaK-4 or BAK4 ? (1 Viewer)

[Ted Y.]

It seems the standard for BaK-4 is not universal.
"It has been pointed out to me that many Chinese optical devices labeled as having BAK4 prism glass are not actually the same as the Schott BaK-4 ones. "
"Not only this, but the tolerances for bubble density is much laxer for Chinese BaK4 (PSK3); it permits twice the bubble density that is permitted in Schott BaK4"

If so, how important it is for a binocular user?

 

[Tringa45]

It's all rather confusing. There are two distinctly different glass types from Schott, N-BAK4 with a glass code 569560 and from the Chinese manufacturer, CDGM, H-BaK4 with glass code 552634.
Schott BAK4 has a refractive index of 1,569 (first thre digits of the code) and an Abbe No. of 56,0 (last three digits)
CDGM BaK4 has a refractive index of 1,552 and an Abbe No. of 63,4. CDGM give the Schott equivalent as N-PSK3! (Phosphate heavy crown).
I believe both are Barium crown (Barium-Kron), so why don't Schott call it BaK4 in line with the chemical symbol?
Here's a data base: RefractiveIndex.INFO - Refractive index database. Alternatively you can download the specs from the manufacturers websites.

John

 

[BKoh]

It seems the standard for BaK-4 is not universal.
"It has been pointed out to me that many Chinese optical devices labeled as having BAK4 prism glass are not actually the same as the Schott BaK-4 ones. "
"Not only this, but the tolerances for bubble density is much laxer for Chinese BaK4 (PSK3); it permits twice the bubble density that is permitted in Schott BaK4"

If so, how important it is for a binocular user?

The only thing that matters is the final optical performance, for which user reviews are a good guide, best if you test the bino yourself.

For budget binoculars, quality control is probably more important than the optical design - basic designs that work well are not a secret.

The type of glass used in the prisms tells you nothing about manufacturing quality control. For budget binos I would buy from a place that allows returns. If I get a good copy, I keep it. If not, I return it. Proper collimation and absence of excess glue/grease/dust inside the optics are more important than what kind of glass the prisms are made of.

 

[Troubador]

It's all rather confusing. There are two distinctly different glass types from Schott, N-BAK4 with a glass code 569560 and from the Chinese manufacturer, CDGM, H-BaK4 with glass code 552634.
Schott BAK4 has a refractive index of 1,569 (first thre digits of the code) and an Abbe No. of 56,0 (last three digits)
CDGM BaK4 has a refractive index of 1,552 and an Abbe No. of 63,4. CDGM give the Schott equivalent as N-PSK3! (Phosphate heavy crown).
I believe both are Barium crown (Barium-Kron), so why don't Schott call it BaK4 in line with the chemical symbol?
Here's a data base: RefractiveIndex.INFO - Refractive index database. Alternatively you can download the specs from the manufacturers websites.

John

What about Ted's question concerning bubble density?

Lee

 

[Tringa45]

What about Ted's question concerning bubble density?

Lee

I think most optical glass manufacturers will offer their products with varying tolerances of homogeneity and bubble content.
Here are a couple of links if anyone's interested: https://mss-p-009-delivery.stylelab...451e82bf70b480b0874d?v=47ebbb91&download=true

https://mss-p-009-delivery.stylelabs.cloud/api/public/content/84be1c65693844f095ed4d684e358725?v=c3f1af67&download=true

The requirements for an Astro Physics refractor would probably be much more demanding than for any binocular.

John

 

[Troubador]

I think most optical glass manufacturers will offer their products with varying tolerances of homogeneity and bubble content.
Here are a couple of links if anyone's interested: https://mss-p-009-delivery.stylelab...451e82bf70b480b0874d?v=47ebbb91&download=true

https://mss-p-009-delivery.stylelabs.cloud/api/public/content/84be1c65693844f095ed4d684e358725?v=c3f1af67&download=true

The requirements for an Astro Physics refractor would probably be much more demanding than for any binocular.

John

Thanks John

Lee

 

[Eric_D]

It's all rather confusing. There are two distinctly different glass types from Schott, N-BAK4 with a glass code 569560 and from the Chinese manufacturer, CDGM, H-BaK4 with glass code 552634.
Schott BAK4 has a refractive index of 1,569 (first thre digits of the code) and an Abbe No. of 56,0 (last three digits)
CDGM BaK4 has a refractive index of 1,552 and an Abbe No. of 63,4. CDGM give the Schott equivalent as N-PSK3! (Phosphate heavy crown).
I believe both are Barium crown (Barium-Kron), so why don't Schott call it BaK4 in line with the chemical symbol?
Here's a data base: RefractiveIndex.INFO - Refractive index database. Alternatively you can download the specs from the manufacturers websites.

John

Schott use N- prefixes to indicate 'lead and arsenic free', and P- prefixes for low 'melting' (or transition) temperature lead and arsenic free glasses for moulding (not grinding) processing.
Schott Glass no longer use the name BaK4 instead of BAK4.
The Chinese use different chemistry to achieve much the same optical properties. Phosphorus not Barium.
Some bino sources say 'Barium Crown' is 'baritleichkron' in German, but that seems to be a typo for 'baritleichtkron'. 'Leicht' is 'light (weight)', although BaK4 is heavier than BK7. Maybe 'baritleichtkron' has less barium than barium-rich 'baritkron'? There is also 'BaLK'.

Sources

 

[jring]

Hi,

the glass quailty can safely be ignored for a low performance application like binoculars... unless you get to defects like visible bubbles or optical data way off the usual quality scales...

Joachim