STANDARD PLATE GLASS MIRROR BLANKS

(APPROXIMATE MEASUREMENTS)

DESCRIPTION

DIAMETER

THICKNESS

WEIGHT

PART #

1.50"

1.000"

0.16

SPG150

2.00"

1.000"

.29

SPG200

3.00"

1.000"

.65

SPG300

4.00"

1.000"

1.10

SPG400

4.25"

1.000"

1.30

SPG425

4.50"

1.000"

1.55

SPG450

5.00"

1.000"

1.80

SPG500

6.00"

1.000"

2.60

SPG600

7.00"

1.200"

4.35

SPG700

8.00"

1.375"

6.50

SPG800

9.00"

1.500"

8.90

SPG900

10.00"

1.750"

12.75

SPG1000

11.00"

1.800"

16.50

SPG1100

12.50"

2.125"

24.00

SPG1250

 

Standard plate glass blanks are supplied with flat faces (Plano-Plano) with one face surface ground flat. If a mistake is made on one surface, the blank can be turned over and the fabricator can make a second attempt at generating the required curvature. These blanks are all fine annealed material.

Plate glass blanks offer the fabricator a slightly less expensive alternative to Pyrex blanks and may be desirable for a first mirror attempt or for educational training. The primary disadvantage with using a plate glass blank as a primary mirror is its high coefficient of expansion which has an injurious effect on the figure caused by temperature changes, i.e., image distortion until the blank’s temperature normalizes with the surrounding temperature. The coefficient of expansion (.00000891 per degree Centigrade) of   plate glass is approximately three times that of Pyrex.

The largest plate-glass mirror in use is the 100 inch, f/5.1, at Mount Wilson Observatory. However, since 1934 most of the large observatory mirrors and commercial telescope mirrors have made from material having a lower coefficient of expansion than that of plate glass, i.e., Pyrex, fused silica, fused quartz, low-expansion ceramic glasses, etc.

It should be noted , however, that many of the domestic telescope manufacturers are currently using plate glass blanks in some of their products.

Grinding tools (plate glass blanks) can be purchased elsewhere in this catalog.

CUSTOM PLATE GLASS BLANKS

*It should be noted that other blank sizes or configurations can be made to the fabricator’s specifications. Please submit a drawing with the dimensional specification to facilitate our quotation process.