[UCANSEE2]

Radio telescopes detect photons.

Radio telescopes detect whatever segment of the electromagnetic spectrum we tune them to.

Visible light (an extremely tiny part of the spectrum) is easily obscured and not as useful as other frequencies of the spectrum.

[Cboldt]

I figure the scope of meaning associated with "photon" varies from person to person, but technically, all electromagnetic radiation, from very low frequency, to radio, to microwave, to visible light, to x-rays, to high energy, all of that comprises photons.

In other words, "photons" technically covers more spectrum than the (human) visible spectrum of electromagnetic energy. Radio telescopes capture photons, just as optical telescopes do.