10 Largest Optical Telescopes

The word "largest" can be a tricky word. So the list is split into traditional single-instrument optical telescopes on a single mount, and into interferometric "virtual" telescopes consisting of multiple optical instruments whose images are combined. Also see 10 largest radio telescopes.

Single telescopes

These are the 10 largest single-instrument, single-mount optical telescopes in the world:

1. Large Binocular Telescope (LBT) *

11.9 m effective (2 x 8 m) / 469 inches
Mt Graham, AZ USA

2. Gran Telescopio Canarias (GTC)

10.4 m / 409 inches
La Palma, Canary Islands, Spain

3. Hobby–Eberly Telescope (HET)

10 m / 394 inches
Mt Fowlkes TX USA

4. Keck I **

10 m / 394 inches
Mauna Kea, HI USA

5. Keck II **

10 m / 394 inches
Mauna Kea, HI USA

6. South African Telescope (SALT)

9.2 m / 362 inches
Sutherland, South Africa

7. Very Large Telescope (VLT) ***

8.2 m / 323 inches (UT-1 thru UT-4)
Cerro Paranal, Chile

8. Subaru Telescope

8.2 m / 323 inches
Mauna Kea, HI USA

9. Gemini North

8.1 m / 319 inches
Mauna Kea, HI USA

10. Gemini South

8.1 m / 319 inches
Cerro Pachon, Chile

* Counts as a single instrument, just like a pair of binoculars.

** Keck I and II were originally designed to be used as an optical interferometer, but funding never materialized for the additional equipment needed.

*** The four VLT telescopes can be used either individually or combined as a single optical inteferometer.

Interferometer-array telescopes

Although relatively common in the radio-spectrum domain, optical interferometry where images from multiple telescopes are combined to form a single image is fiendishly difficult and rare. Interferometric telescopes in essence form a large "virtual" telescope with an effective aperture based on the distance between the member telescopes.