Question: What is an example of a gamma ray telescope?
About the article "Telescope", section "Gamma-ray telescopes".

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Higher energy X-ray and Gamma-ray telescopes refrain from focusing completely and use coded aperture masks: the patterns of the shadow the mask creates can be reconstructed to form an image.X-ray and Gamma-ray telescopes are usually on Earth-orbiting satellites or high-flying balloons since the Earth's atmosphere is opaque to this part of the electromagnetic spectrum.
However, high energy X-rays and gamma-rays do not form an image in the same way as telescopes at visible wavelengths.
An example of this type of telescope is the Fermi Gamma-ray Space Telescope.
The detection of very high energy gamma rays, with shorter wavelength and higher frequency than regular gamma rays, requires further specialization.
An example of this type of observatory is VERITAS.
Very high energy gamma-rays are still photons, like visible light, whereas cosmic rays includes particles like electrons, protons, and heavier nuclei.
A discovery in 2012 may allow focusing gamma-ray telescopes.
At photon energies greater than 700 keV, the index of refraction starts to increase again.
The High Altitude Gamma Ray Telescope (HAGAR) is an atmospheric Cerenkov experiment with 7 telescopes setup in 2008.
Each telescope has 7 mirrors with a total area of 4.4 square meters.
The telescopes are deployed on the periphery of a circle of radius 50 meters with one telescope at the center.
Each telescope has alt-azimuth mounting. 
VERITAS (Very Energetic Radiation Imaging Telescope Array System) is a major ground-based gamma-ray observatory with an array of four 12m optical reflectors for gamma-ray astronomy in the GeV - TeV energy range.
VERITAS uses Imaging Atmospheric Cherenkov Telescope technique to observe gamma-rays.
The telescope design is based on the design of the existing 10m gamma-ray telescope of the Fred Lawrence Whipple Observatory.
It consists of an array of imaging telescopes deployed such that they permit the maximum versatility and give the highest sensitivity in the 50 GeV - 50 TeV band (with maximum sensitivity from 100 GeV to 10 TeV).
This very-high-energy observatory, completed in 2007, effectively complements Fermi. 
INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a currently operational space telescope for observing gamma rays.
It was launched by the European Space Agency into Earth orbit in 2002, and is designed to detect some of the most energetic radiation that comes from space.
It is the most sensitive gamma ray observatory ever launched.INTEGRAL is an ESA mission in cooperation with the Russian Space Agency and NASA.
It has had some notable successes, for example in detecting a mysterious 'iron quasar'.
It has also had great success in investigating gamma-ray bursters and evidence for black holes. 
The Fermi Gamma-ray Space Telescope (FGST), formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit.
Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter.
Another instrument aboard Fermi, the Gamma-ray Burst Monitor (GBM; formerly GLAST Burst Monitor), is being used to study gamma-ray bursts.
Fermi was launched on 11 June 2008 at 16:05 GMT aboard a Delta II 7920-H rocket.
The mission is a joint venture of NASA, the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.