Placing a CCD array at the prime focus of a telescope or observatory is a surefire way to get an outstanding image; a technique that’s been in use for well over 100 years. But is it possible to use CCDs in place of a mirror or lens entirely? Image credit: Large Area Imager for Calar Alto (LAICA) / J.W. Fried.

Ask Ethan: Why don’t we build a telescope without mirrors or lenses?

Why not just put your detectors in place of a giant mirror?

“Look and think before opening the shutter. The heart and mind are the true lens of the camera.” -Yousuf Karsh

For hundreds of years, the principle behind the telescope has been as simple as it gets: build a lens or mirror to collect a large amount of light, focus that light onto a detector (like an eye, a photographic plate, or an electronic device), and see far beyond the capabilities of your unaided vision. Over time, lenses and mirrors have gotten bigger in diameter and have been crafted to higher precision, while detectors have advanced to the point where they can collect and make good use of every single incoming photon. The quality of detectors might make you wonder why we bother with mirrors at all! That’s what Pedro Teixeira wants to know:

Why do we need a lens and a mirror to make a telescope now that we have CCD sensors? Instead of having a 10m mirror and lens that focus the light on a small sensor, why not have a 10m sensor instead?

It’s a very astute question, because if we could do this, it would be revolutionary.