1.1 classification of optical glass types
according to the position and glass composition of refractive index (nd) and dispersion coefficient (υd) in nd-υd domain diagram, optical glass types are classified into the 17 groups shown in the following table.
group | code | group | code |
fluor crown | fk | light flint | qf |
light crown | qk | flint | f |
phosphate crown | pk | barium flint | baf |
crown | k | dense barium flint | zbaf |
barium crown | bak | dense flint | zf |
dense crown | zk | lanthanum flint | laf |
lanthanum crown | lak | dense lanthanum flint | zlaf |
crown flint | kf | titanium flint | tif |
|
| special flint | tf |
each optical glass type is designated by its glass group code and a number. in addition to our glass type designation, a six-digit code is used in this catalog. the first three digits indicate the first three numbers after the decimal point of nd while the last three digits represent the abbe-number. for example, f4 with nd=1.62005 and υd=36.35 is indicated by its six-digit code 620-364.
glass types which exclude lead, arsenic, cadmium and radioactive elements from their compositions are distinguished by the prefix, ＂h＂, for example, h-f4.
environment-friendly low softening point glass type for molding is expressed by a prefix “d-”, for example, d-lak6.
according to the clients’ adjustment demand of refractive index, “-refractive index variation” or “-m refractive index” is added to the end of the original names. the letter m means the refractive index is reduced. otherwise, the refractive index is increased. take d-zlaf52n and d-laf50 for example. if the refractive index (nd) of d-zlaf52n is reduced by 170×10-5, the new material will be named as “d-zlaf52n-m170”. if the refractive index (nd) of d-laf50 is increased by 170×10-5, the new material will be named as “d-laf50-170”.
high transmittance glass is suffixed with “gt”, which refers to the first letter in pinyin “gao tou”, for example, h-zf7lgt.
if the optical constant is slightly adjusted, suffix “l” or “n” will be added to the end of the original material name. “l” means the refractive index or abbe number is slightly lower than the original material while “n” shows the refractive index or abbe number is slightly higher than the original material.
if the optical constants aren’t changed while their formulation is modified to improve other properties, the prefix “a”, “b”, “c”…… “f” will be added to the end of the material name according to the sequence.