Perhaps you are thinking of a radio telescope, although your question is quite open-ended.
Voltmeters, frequency counters, and trombones also fit the description.
Neither the violin nor the Eb Sousaphone does.
An optical telescope.
telescope
The observatory had not yet opened, so we waited outside until it did.
telescope
Radio Telescope Apex
There is a 3 metre radio telescope on the roof of Cardiff University. There is also an optical telescope at the site for the use of undergraduates.
The instrument scientists use to observe the planets is a high powered telescope.
telescope
telescope
Some design variants you may see in an optical telescope include telescopes that fold or divert the optical path with mirrors and telescopes that use special lenses to enhance the images.
Telescope.