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The main forms are as follows:

7.1 Optical glass blocks

Blocks are fine-ground on two large sides, coarse-ground on other four sides, with all edges and angles slightly chamfered. Optical glass blocks are fine-annealed.


7.2 Glass strips

The abscission sides which are cut at standard or custom lengths exhibit naturally transparent surfaces, while all other sides exhibit naturally formed or rolled surfaces. Glass strips may be fine or coarse annealed.


7.3 Optical glass pressings

7.3.1 Direct pressings of optical glass (DP)

Direct pressings are formed by directly pressing molten glass from melter. DPs are then fine annealed.

7.3.2 Reheat pressings of optical glass (RP)

Reheat pressings are shaped by heating and forming gobs that are cut and processed to a specified mass and volume as determined by the resultant molded blank. RPs are then fine annealed. Outer diameters and thickness tolerance for lens blanks are shown in Table 14.


Table 14

Outer diameter

(mm)

DP product

RP product

Tolerance of outer diameter(mm)

Tolerance of thickness(mm)

Tolerance of outer diameter(mm)

Tolerance of thickness(mm)

<12

±0.10

±0.20

±0.10

1.0

12~40

±0.15

±0.20

±0.15

0.5

41~60

±0.20

±0.20

±0.20

0.5

61~90

±0.30

±0.30

±0.30

0.6

91~150

±0.40

±0.40

±0.40

0.6

>150

±0.50

±0.50

±0.50

0.7

 

7.4 Optical glass gobs

Gobs are coarse annealed blanks with a nearly round cross section. The weight or volume is based on customers’ requirements.

 

7.5 Others
The glass can be produced as customers’ special specifications and requirements.

We have listed NHG’s glass types and corresponding types from HOYA, OHARA, HIKARI and SCHOTT. In this comparative table, the same glass type only means the same glass code, not means the same glass composition.

Glass types are listed in order of higher refractive index (nd) and lower Abbe-number (υd) when refractive index is the same.



 

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