OHARA INC.

Each optical glass has its own properties which are closely connected with the key chemical elements contained.
With this in mind, we have developed and are using a new glass type designation system.
On the nd-νd diagram located in the rear of this catalog, you will see we have divided our glasses into groups. For each glass type, we have selected one or two chemical elements contained which are considered the most important and have used the atomic symbols of these for the first two letters of the glass type designation.
The third letter of the glass type designation refers to the refractive index of each glass type within its glass group: H, M or L for high, middle, or low.
Lastly we assign a one or two digit number to each glass type within a given glass family. Thus each glass model number is represented by the above-mentioned three letters plus a one or two digit number.
For example, the glass type designation for S-BSL7 is composed as follows: S-stands for environmentally Safe, B represents Boron, S represents Silicon, L indicates a Low index within the BS glass group, and 7 indicates this is the 7th glass within this glass family.
Along with OHARA's glass type designation, the technical data sheets will show the six-digit code for each glass type.
In the six-digit code the first three digits represent the refractive index at the helium line (nd) and the last three digits represent the Abbe number (νd).
These six-digit codes are internationally recognized within the optical community.

When light passes through glass, its speed falls and its travel distance decrease. This is known as optical path length. From the rate of the speed, refractive index can be calculated. Refractive indices are indicated to five decimal places for 10 spectral lines in accordance with JIS B 7071-1 standard. The principal indices for the d line (587.56 nm) and the e line (546.07 nm) are indicated to six decimal places.   Table 1

Spectral Line Symbol	s	A´	C	He-Ne	d	e	F	g	h	i
Light Source	CS	K	H	Laser	He	Hg	H	Hg	Hg	Hg
Wavelength (nm)	852.11	768.19	656.27	632.8	587.56	546.07	486.13	435.835	404.656	365.015

In refractive index section on the data sheet, the wavelengths of individual spectral lines are stated in nanometers (nm) to the right of the symbol.

Dispersion refers to the phenomenon arising from a variation in the refractive index depending on the wavelength. As principal dispersion, (n_F-n_C) and (n_F´-n_C) are indicated. The data sheet indicates the dispersion calculated from the refractive index to six decimal places. Abbe number is indicated to two decimal places. Two decimal places: This is result of calculation from nd to six decimal places (with seven effective digits) and the principal dispersion to six decimal places (with four or more effective digits)

For the wavelengths (x and y), in order to have effective achromatization, a certain desirable relationship is required between the relative partial dispersion [ θ_x,_y=(n_x-n_y)/(n_F-n_C) ] and the νd. As a means of representing the relationship between θ_x,y and ν_d of different glass types the chart of θ_g,Fand ν_dis published. In this chart, a large number of glass types are distributed along a fixed trend line. The glass types that are outliers from this trend line tend to have anomalous dispersion. To represent anomalous dispersion numerically, after plotting 511605(NSL7) and 620363(PBM2) on the θ_x,y-ν_d diagram, then the straight line between these two points is drawn. Then the difference in vertical direction between position of glass type and straight line is listed as Δθ_x,y. NSL7 and PBM2 are glass types that have been already discontinued at Ohara. However, it's been decided to continue to use of these 2 glass types because the baseline for representing the anomalous dispersion should not be changed. Table 2

	θg,F	θc,t	vd
NSL7	0.5436	0.8305	60.49
PBM2	0.5828	0.7168	36.26

Refractive index of the glass will change by influences of temperature. The change of refractive index by temperature can be ascertained through the temperature coefficient of refractive index, and it is defined as Δn/ΔT from the curve showing the relationship between glass temperature and refractive index. Δn/ΔT depends on wavelength, and also varies with temperature. Therefore, the Abbe number also changes with temperature. There are two ways of showing the temperature coefficient of refractive index. One is the relative coefficient [ Δn_rel/ ΔT] measured in the air (101.3 kPa {760 torr} dry air) at same temperature as glass and the other is the absolute coefficient [ Δn_abs/ΔT ] measured under vacuum. In this catalog, by the method referred to JIS B 7072-1 and JIS B 7072-2, [ Δn _rel/ΔT ] which is usually used in optical design is listed at the wavelengths 589.29nm (D) and the temperature range from 40˚C to 80˚C. The absolute temperature coefficient of refractive index (Δn_abs/ΔT) can be calculated by the following formula: Δn_abs/ΔT = Δn_rel/ΔT ＋ n_abs(T₁)＋n_abs(T₂)/2 × Δn_air/ΔT T₁:[ Δn_rel/ΔT ] Temperature at the lower boundary of the temperature range (°C) T₂:[ Δn_rel/ΔT ] Temperature at the high temperature boundary of the temperature range (°C) n_abs(T₁) : Absolute refractive index of measurement sample at temperature T₁ n_abs(T₂) : Absolute refractive index of measurement sample at temperature T₂ Table 3 shows the temperature coefficient of refractive index of air.

On the basis of the JOGIS-02, Coloring can be determined by measuring spectral transmission, including reflection losses with test pieces of 10 mm in thickness. The wavelengths corresponding to 80% transmission and 5% transmission are indicated as 405/355 in units of 5nm The values are grouped into steps of 5 nm using this rounding method: the range 0 nm to 2 nm counts as 0 nm, the range 3 nm to 7 nm counts as 5 nm, and the range 8 nm to 10 nm counts as 10 nm. For glass types with a high refractive index of n_d ≧1.84, the wavelength showing transmittance of 70% was used instead of 80%, because the reflection loss is large. The indication has been made as (415).  

As a simplified indicator of coloring, the wavelength values in nm at which the internal transmittance of a 10 mm thick glass sample is 0.80 and 0.05 are indicated.

ISO Colour Contribution Index (ISO/CCI): The color characteristic index calculated by the method referred JIS B7097-1986. CCI is an index indicating "the amount of color variation caused by the spectral characteristics of lens" comparing with the original color when photographed. In this catalog, in order to refer to the influences caused by the glass material itself, the index is listed. For more information, please refer to JIS B 7097 "Determination of ISO Colour Contribution Index (ISO/CCI) of Camera Lenses".

We implement Water Resistance (Powder Method) and Acid Resistance (Powder Method) for the reference of "dimming" or "staining". These tests are conducted using the method in accordance with JOGIS-06. The glass to be tested is crushed to 425μm ~ 600μm grains. A sample of this powder equivalent to the specific gravity in grams is placed on a platinum basket. This is put in a flask of glass containing the reagent and boiled for 60 minutes. The sample is then carefully dried and re-weighed to determine the loss of weight (percent) and classified as per Tables 4 and 5. The reagent used for the water resistance test is distilled water (pH 6.5 ~ 7.5). 1/100N nitric acid is used for the acid resistance test.

(Table 4) Water Resistance

Class	1	2	3	4	5	6
Weight loss(%)	＜0.05	≧0.05 ＜0.10	≧0.10 ＜0.25	≧0.25 ＜0.60	≧0.60 ＜1.10	≧1.10

 

Class	1	2	3	4	5	6
Weight loss(%)	＜0.20	≧0.20 ＜0.35	≧0.35 ＜0.65	≧0.65 ＜1.20	≧1.20 ＜2.20	≧2.20

This test is carried out by putting freshly polished glass plates in a chamber at +60°C, 95% humidity for 24hours. If the glass surface is severely attacked, another 6 hours test is carried out with new pieces. The classification into four class is then obtained by inspecting the treated surface through a 50x microscope as per Table 6.

By the method referred to ISO-8424, the glass samples size 30×30×3mm with 6 faces polished in the specified condition, are hung into nitric acid solution (pH 0.3) or acetic acid buffer solution (pH 4.6) at 25°C for specified times (10minutes, 100minutes, 16hours, 100hours). After the treatments, the samples are weighed to determine the loss in mass. Calculation of the time(h) required in order to attack a surface layer to a depth of 0.1μm is done using the following formula: t_0.1=t_e・d・s/(m₁–m₂)・100 t0.1 :the time (h) decreases a surface layer at a depth of 0.1μm te : the time (h) for attack in the experiment d : the specific gravity of the sample S : the surface area(cm²)of the sample m1,m2:the mass (mg) of the sample before and after the test The calculation is carried out by use of the value of the loss of mass which is observed by the minimum test condition (i.e.,test solution and test time) for obtaining a loss of mass greater than 1mg / sample. If the loss of mass is less than 1mg / sample after 100 hours exposure to pH 0.3, this value shall be accepted. The acid resistance class SR is obtained by comparison of the pH of the test solution and the time required for the attack to a depth of 0.1μm (h) with time scales given in the classification Table 7.

Table 7

Acid resistance class SR	1	2	3	4	5		51	52	53
pH of the attacking solution	0.3	0.3	0.3	0.3	0.3	4.6	4.6	4.6	4.6
The time(h) decreases a surface layer at a depth of 0.1μm.	＞100	≦100 ≧10	＜10 ≧1	＜1 ≧0.1	＜0.1	＞10	≦10 ≧1	＜1 ≧0.1	＜0.1

In addition, changes in the surface of the sample following the treatment are qualitatively evaluated with the naked eye. Additional classification numbers are given according to Table 8. Table 8 For example, it is indicated that the acid resistance class SR is SR 3.2 for the optical glass which needs 2 hours for the attack to a depth of 0.1μm by an attacking solution of pH 0.3 and with interference colors after the attack.

the specified condition are prepared and they are hung into aqueous solution containing 0.01 mol/l purified tripolyphosphate at 50°C for specified times (15minutes, 1hour, 4hours, 16hours). By the method referred to ISO-9689. After this treatment, the loss of mass of the sample is determined using an analytical balance. Calculation of the time decreases a surface layer at a depth 0.1μm is made using the same formula which is used for obtaining the acid resistance (SR) in the previous section. In this case, however, the time units are minutes. The calculation is carried out, as a rule, using the value of the loss of mass which is observed under the minimum test conditions (i.e.,test solution and test time for obtaining a loss of mass greater than 1 mg / sample). The phosphate resistance class PR is obtained by comparison of the time required for the attack to a depth of 0.1μm (min) with time scales given in classification Table 9.

Table 9

Phosphate resistance class PR	1	2	3	4
The time decreases a surface layer at a depth of 0.1μm(min)	＞240	≦240 ≧ 60	＜60 ≧15	＜15

Next, changes in the surface of the sample following the treatment are qualitatively evaluated with the naked eye. Additional classification numbers are given in addition to the class number according to Table 8 used for obtaining the acid resistance (SR) in the previous section. For example, it is indicated that the phosphate resistance class is PR 2.0 for optical glass which needs 120 minutes for attack to a depth of 0.1μm, with no visible changes in the surface after the attack.

Transformation Temperature (Tg) refers to the temperature at which the glass transforms from a lower temperature glassy state to a higher temperature super-cooled liquid state. Transformation temperature can be determined from the thermal expansion curve in Figure 2. The yield point is shown for the temperature when deformation starts because of the measured pressure (load) exerted on the specimen at the time of measuring expansion, as shown in Figure 2.

The softening point is the temperature at which glass deforms under its own weight. Viscosity of the glass is 10^7.65 dPa·s { poise } at this temperature. The softening point is measured by the Fiber Elongation Method referred to JIS-R3103.

The annealing point corresponds to the maximum temperature in the annealing range at which the internal strain of glass will be substantially eliminated. Viscosity of the glass is 10¹³ dPa·s {poise} at this temperature. The annealing point is measured by the Fiber Elongation Method referred to JIS-R3103.

By the method referred to JOGIS-16 and the JOGIS-08, the thermal expansion curve is obtained by measuring a well-annealed glass sample of 4 mm diameter by 50 mm long heated at a rate of 2˚C/min in the low temperature range and at a rate of 4˚C/min in the high temperature range. From the temperature and elongation of the sample glass, the mean linear coefficient of thermal expansion from –30˚C to +70˚C and from +100˚C to + 300˚C respectively up to 10^–7/K is determined and is given in the catalog.

The thermal conductivity value of most optical glasses at room temperature is between the range of 1.130 W/(m·K) for S-BSL7 to 0.599 W/(m·K) for S-PHM52 and it is measured using the transient hot wire method. The thermal conductivity of glass at temperature of 35˚C is listed in this catalog. The measurement accuracy is ±5%.

Knoop hardness is an indicator of hardness for a substance. The indentation hardness of optical glass is determined with the aid of the micro hardness tester. One face of the specimen with the necessary thickness is polished. The diamond indentor is formed rhombic so that the vertically opposite angle from two axes is 172°30' and 130° respectively. The load time is 15 seconds, the load is 0.98 N { 0.1 kgf }. Knoop hardness =1.451・F/ι² F ： Load (N) ι： Length of longer diagonal line (mm) Table 10 shows how the glasses are classified by the method referred to JOGIS-09. This catalog shows both the class and the Knoop hardness figures have been rounded to the nearest 5 (e.g. value of 158 is shown as 160.)

Table 10

Class	1	2	3	4	5	6	7
Knoop Hardness	＜150	≧150 ＜250	≧250 ＜350	≧350 ＜450	≧450 ＜550	≧550 ＜650	≧650

 

Abrasion is an indicator of how easy or difficult glass is ground at the processing. In accordance with a method based on JOGIS way, a sample of size 30 x 30 x 10 mm is lapped on a 250 mm diameter cast iron flat, rotating at 60 rpm. The test piece is located 80 mm from the center of the flat and is under a 9.8N { 1 kgf } load. 20 ml of water containing 10 g of aluminous abrasive as the lapping material, with mean grain size #800, is supplied evenly to the test piece for 5 minutes. The weight loss of the test piece is then measured. The known weight loss of the standard glass is compared according to the following formula. The values calculated with the formula are showed to the nearest integer as the abrasion data. Abrasion =(wear mass of specimen / specific gravity) /(wear mass of standard / Specific gravity of standard sample) ×100

Optical glass is usually free of strain, but when mechanical or thermal stress is exerted upon it, glass shows birefringence. Stress F(Pa), optical path difference σ(nm) and thickness of glass d(cm) have the following relationship: σ=β・d・F In this case, proportional constant β is called the photoelastic constant. It is listed in this catalog at a unit of (nm(cm/10⁵ Pa)). The photoelastic constant is the material constant which will change by glass type. By using it, optical path difference can be computed from given stress. Internal stress can also be computed from optical path difference.

Specific gravity is the density value of well-annealed glass referenced against pure water at 4°C, with the value shown to 2 decimal places.The measurement is performed using the method in Standard No. JIS Z8807.

Refractive indices and Abbe number, which are given in this catalog, are the representative value of plural melting lots. The values of the melting lot delivered will be within the tolerances specified below: [ Optical Glass for Polished Lenses ] n_d : ±30×10^-5 ν_d : ± 0.5% (rounded up to the guaranteed number of digits) Upon special request, and depending upon the glass types, the following tolerances can be accepted : n_d : ±20×10^-5 ν_d : ±0.3% (rounded up to the guaranteed number of digits) In the supply of our standard products, Melt Data is attached and includes the following data : - Refractive indices: the measurement values of each spectral lines (C, d, F, g ). These are shown to 5 decimal places. (effective number: six digits) - Abbe numberνd: the calculated value by the measured refractive indices. These are shown to 1 or 2 decimal places. e.g. S-BSL7 n_d : 1.51633 ± 0.00030 ν_d : 64.14 ± 0.33 For special requirements, other than what is mentioned above, please contact us. [ Optical Glass for Glass Mold Lenses ] RC value : Standard RC value± 30 (Raw material control value) ν_d : ± 0.5% (rounded to the guaranteed number of digits) When products are supplied, the RC value is given to Melt No.. This RC value is Δnd at 5 decimal places concerning the material that underwent OHARA’s standard annealing (-600°C per day). The RC value is rounded to 4 decimal places and shows with a unit of 10^-5. And it comes with a report of theνd value to 1 or 2 decimal places concerning the product after annealing as specified in catalog annealing (-200°C per day). e.g. L-BSL7 RC value : -30 ± 30 ν_d : 64.06 ± 0.33 The standard measurement accuracy for refractive index and dispersion is as follows : Refractive index : ±3×10^-5 Dispersion : ±2×10^-5 On request, we shall measure at precision accuracy as follows : Refractive index : ±1×10^-5 Dispersion : ±3×10^-6 For ultra-precision measurements and reading at spectral lines not described in this catalog, please contact us.

For glass used in very precise lens systems it is sometimes necessary to measure the refractive index variation across a blank. In such cases, Ohara pays special attention to each process and can supply high homogeneity glass. The homogeneity is measured by calculating PV value of refractive index fluctuation width (excluding linear change component of refractive index) using computer analysis of the transmitted wavefront of a planeparallel glass sample with the phase-measuring interferometer. In case that the value of the change amount PV value must be guaranteed within ±2×10^-5, measurement of an individual product is conducted and the value of the change amount is guaranteed at six decimal places (10^-6). Note: The homogeneity of our general glass products could exceed ±2×10^-5, depending on glass type, dimensions, shape, etc.

In case that glass retains residual strain, this can be observed as optical birefringence. The amount of stress is measured by optical path differences and specified in nm/cm. On special request, when we measure stress birefringence in detail, a rectangular plate is measured 4 points loacated 5% from the edge at the middle of the each side. A disc is measured at 4 points located 5% from the edge of the diameter. The maximum value of the 4 points is shown as the birefringence value and is categorized based on Table 11. For other special forms and shapes the points to be measured will be determined. Table 11

Class	1	2	3	4
Birefringence(nm/cm)	＜5	≧5 ＜10	≧10 ＜20	≧20

 

In case that glass retains residual strain, this can be observed as optical birefringence. The amount of stress is measured by optical path differences and specified in nm/cm. On special request, when we measure stress birefringence in detail, a rectangular plate is measured 4 points loacated 5% from the edge at the middle of the each side. A disc is measured at 4 points located 5% from the edge of the diameter. The maximum value of the 4 points is shown as the birefringence value and is categorized based on Table 11. For other special forms and shapes the points to be measured will be determined.

Table 12

Striae Class	Striae Content Using Striaescope
1	No visible striae
2	Striae is light and scattered
3	Striae is heavier than Class 2

It is most desirable to manufacture bubble-free optical glass, but the existence of bubbles to some extent is inevitable. Bubbles in optical glass vary in size and number from one glass to another due to the many different compositions and production methods. The classification of bubble content is established by specifying in mm2 the total bubble cross sections existing in 100cm3 of glass volume. Inclusions such as small stones or crystals are treated as bubbles. The bubble classes are shown in Table 13. The classification includes all bubbles and inclusions measuring larger than 0.03 mm.

Table 13

Class	1	2	3	4	5
100cm3The total cross section of bubbles(mm2/100cm3)	＜0.03	≧0.03 ＜0.1	≧0.1 ＜0.25	≧0.25 ＜0.5	≧0.5

Variation of coloring between melting lots is generally within ±10 nm. On special request, we shall report the coloring or the transmission, of the melt to be supplied by measuring spectral transmission.

We showed each properties as representative value except for 7.1~7.6. Please contact us when you want to know the other value. In addition, please let us know your preferred specification when you place the orders.

Strip Glass is made by drawing glass out of a furnace. Strips are rectangular in shape, have slightly rippled fire-polished surfaces (unworked), and are flame cut to the required lengths. The corners are round. Strips are coarse or fine annealed. This is the least expensive form of supply. Thickness 15 ~ 40mm Width and Length 50 ~ 200mm The above are standard strip sizes but there are exceptions for certain glass types. Please contact our sales department with your specific requirements.

Reheat pressings are the product molded in heat press to shapes suitable for spherical polished lenses and prisms. Please specify followings: 1 ) Diameter (including grinding stock) 2 ) Center Thickness (including grinding stock) 3 ) Radii of curvature 4 ) Glass quality (striae, bubble, etc.) 5 ) Chamfer The standard diameter range and the dimensional tolerances of these blanks are shown in Table 14.

Diameter	Outer & Inner Diameter Tolerance[Range]	Cener Thickness Tolerance[Range]
D ≦φ18 (mm)	0.2 (mm)	1.0 (mm)
φ18＜D ≦φ30	0.3	0.8
φ30＜D ≦φ50	0.4	0.6
φ50＜D ≦φ70	0.6	0.6
φ70＜D ≦φ100	0.6	0.8
φ100＜D ≦φ150	0.8	0.8
φ150＜D ≦φ200	1.0	1.0
φ200＜D ≦φ250	1.2	1.4

Please contact our sales department with your specific requirements.

These blanks are cut from a precision ground rod formed on a centerless grinding machine. The standard diameter range and the dimensional tolerances of these blanks are shown in Table 15. Table 15

Product Size	Diameter Tolerance	Thickness Tolerance
φ3～20mm	0.03mm	0.3mm

Please contact our sales department with your specific requirements.

Followings are handled as the Dimensional Specified Blanks. - Circular blanks - Rectangular blanks - Prism shaped blanks - Special shaped blanks - Fine annealed strips having specified size request

Ohara utilizes our leading edge technology to provide high homogeneity glasses in various glass types. The homogeneity of the products are confirmed by interferometer after striae inspection.

These lenses are polished into a spherical shape. Polished ball can be used as a preform for glass mold lens. For the ball lens dimensions, specifications and other details, please contact us.

Polished preforms are the product polished spherically in a suitable shape to be processed into aspherical glass mold lenses. For the dimensions, specifications and other details on the polished preforms, please contact our sales department.

The lenses have been subjected to double side polishing, centering and coating. For the dimensions, specifications and other details on the polished lenses, please contact our sales department.

Glass mold lenses are the product fabricated by heating and softening polished preforms and transferring it in an ultra-high accuracy aspheric mold and then supplied after centering and coating. For the dimensions, specifications and other details on the polished preforms, please contact our sales department.