segmented mirror

A segmented mirror is a reflector-telescope mirror formed by aligning smaller mirrors (optical segmentation). Keck Observatory pioneered the use of them for large, research telescopes. Alignment must be maintained to a high degree of precision and adaptive alignment is typically performed under computer control. Example telescopes with segmented mirrors:

• Keck
• Hobby-Eberly Telescope (HET)
• Southern African Large Telescope (SALT)
• Gran Telescopio Canarias (GTC)
• James Webb Space Telescope (JWST)
• European Extremely Large Telescope (E-ELT) (under construction)
• Thirty Meter Telescope (TMT) (under construction)
• Giant Magellan Telescope (GMT) (under construction)
• Overwhelmingly Large Telescope (OWL) (plan set aside)

Non-segmented (monolithic mirror) examples:

• Subaru Telescope
• Hale Telescope
• Large Altazimuth Telescope (BTA-6)
• Gemini Observatory (two telescopes)

Also, the Large Zenith Telescope (LZT) had a (non-segmented) liquid mirror.