Science In Your Hands!

5 Inch Telescope Mirror Blank

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Quick Overview

A 5 inch telescope mirror blank is great size for beginning and experienced amateur telescope makers.

- Schott Supremax® 33 borosilicate glass
- Low thermal expansion glass
- molded plano x plano, straight sides
- few to no bubbles
- full thickness (6:1)

5 Inch Telescope Mirror Blank

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  • 5 Inch Telescope Mirror Blank


A 5 inch aperture telescope is a great size for the beginning or expert amateur telescope maker. The first thing you will need to make is your primary. or objective, mirror. With this top quality mirror blank and the appropriate abrasives, polish, and pitch you will be able to make a telescope mirror to your own specifications that can potentially out-perform many mass produced telescopes.

Our 5 inch blanks are made from Schott Supremax® 33 borosilicate glass, the predecessor to Pyrex®, which is no longer made. The advantage to this glass is its low coefficient of thermal expansion which helps your mirror to stabilize quickly as temperature changes through a long night of astronomical discoveries.

Each blank is molded plano on each surface. They have straight sides and few to no bubbles. A diameter to thickness ratio slightly over 6:1 helps prevent flexture in the mirror. Small mold markings are easily ground off as you prepare both sides before you begin grinding your main surface curvature. Precision annealing has also increased the strength of the glass to protect your mirror from thermal shock. This keeps you from losing precious hours of work from a cracked mirror when you eventually pour hot pitch on it.

Additional Information

Glass Type Supremax® 33 Borosilicate Glass
Diameter 5.0 in.
Thickness 1.0 in.
Coefficient of Thermal Expansion 3.25 x 10-6 K-1 (20-300°C / 68-572°F)
Density 2.2 g/cm2
Technical Information Supremax® 33 Borosilicate Glass
Weight 1.65 lbs

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