DxOMark’s ‘perceptual megapixels’ is a simplified summary of lens sharpness on a specific body, not a direct measure of the sensor’s megapixels and not a sign that the lens suddenly becomes worse on a higher-resolution camera.

It compresses complex lens behavior (MTF, center vs edge sharpness, sagittal/tangential performance) into one number. That makes it convenient, but also easy to over-interpret.

Why the numbers vary between bodies:

• different sensor designs
• presence/strength of the anti-aliasing (low-pass) filter
• how the camera resolves fine detail across the frame
• the fact that one summary number hides center/edge tradeoffs

So no, you shouldn’t assume a 24MP body is worse than an 18MP body just because the P-Mpix number is lower. And there is no single ‘optimal pixel count’ for that lens.

In general, a higher-resolution sensor does not make a lens less sharp; it may simply reveal the lens’s limits more clearly. For real comparison, look beyond one aggregate score and check detailed sharpness behavior across the frame, plus real-world sample images if possible.