A lens does not literally have pixels, so “lens resolution in megapixels” is not a native lens specification. In this context, the reviewer was most likely referring to DxOMark’s Perceptual Megapixel (P-MPix) score.

That number is a simplified estimate of how much detail the lens + sensor combination delivers, not the lens alone. It tries to translate optical sharpness into a more familiar “megapixel-like” figure, but it is an oversimplification of a more complex reality.

Lens resolution is more traditionally described by resolving power or MTF (Modulation Transfer Function), often measured using line patterns and expressed in terms like lines per millimeter. Optical resolution also varies with aperture, focus distance, focal length, and image area, so a single “megapixel” number can be misleading.

So if someone says a lens is “9MP,” the practical meaning is: on that camera, the lens may only deliver detail roughly comparable to what a sharper lens would let a 9MP sensor record. It does not mean the extra sensor pixels are useless—higher sensor resolution can still help, even with a modest lens.