Quality
Refractive Index and Abbe Number
Reflective index and Abbe number of fine annealed glass are typically within the following tolerances which are indicated in the present catalog:
nd : ± 50 x 10-5
vd : ± 0.8 %
Upon request, we can supply glass to the following tolerances:
nd : ± 20 x 10-5
vd : ± 0.3 %
Our melt certification contains spectral lines C, d, F and g (measured to the 5th decimal place). Please consult us if there is any special demand for additional spectral lines. The accuracy of standard measurements for refractive index typically are ± 3x10-5. On request we shall provide precision measurements for refractive index ± 1x10-5.
Stress Birefringence
Stress Birefringence is the remaining stress inside the glass depending on the annealing condition. This can be observed as optical birefringence and measured by optical path differences and specified in nm/cm. The following table is the classification by Japanese Optical Glass Industrial Standards (JOGIS1475):
| Grade | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Birefringence (nm/cm) |
< 5 | ≥ 5 < 10 |
≥ 10 < 20 |
≥ 20 |
Striae
Comparing with the Japanese Optical Glass Industry Standards (JOGIS1175) we have the following striae grade of optical glass:
| Grade | Degree of Striae |
|---|---|
| 1 | No visible striae |
| 2 | Standard degree B (Striae is light and scattered) |
| 3 | Standard degree C (Slight striae exist in vertical direction of polished face) |
Bubbles and Inclusions
This specification is determined by taking the sample glass from each melt to measure the total cross-section of bubbles and inclusions. With this value, we determine the grade of the glass.
Coloring
It is hard to avoid the variation of coloring among each glass melts, we have listed the average value in our catalog, the range of variation is generally within ±10nm. On special request, we shall report the coloring of the melts glass to be supplied by measuring spectral transmission in the necessary range of wavelength.