focal spot

The effective area of the anode where X-rays are produced. Smaller focal spots produce sharper images but dissipate heat less efficiently.

Why it matters to buyers: Small focal spot (~0.3 mm) for detail imaging; large (~0.6–1.2 mm) for high-output exposures. Dual focal spot tubes support both.

Why it matters to engineers: Focal spot size degrades with anode wear — visible as image unsharpness creep over time.