Johannes Kepler did not use a telescope in his astronomical observations. He was a contemporary of Galileo Galilei, who was the first to use a telescope for astronomical observations.

While Kepler was aware of Galileo's discoveries and embraced them, he relied on naked-eye observations and the data collected by his mentor, Tycho Brahe, who was known for his precise astronomical measurements.

Kepler's groundbreaking discoveries about planetary motion, like his three laws of planetary motion, were based on analyzing the data meticulously collected by Tycho Brahe.