Yes—either the lens, the body, or both can be affected by a drop, although an 18-inch drop onto carpet may well cause no damage at all.

Autofocus problems after impact are not necessarily “all or nothing.” In an SLR, AF accuracy depends on precise alignment between the lens mount, the AF sensor system, and the imaging sensor. A shock can slightly shift or warp parts so they are no longer perfectly aligned. One common issue is the lens mount no longer sitting exactly parallel to the sensor plane, which can cause focus errors or uneven sharpness across the frame.

The lens can also be affected because it contains moving optical/focus groups and mechanical assemblies that can be knocked out of alignment.

A practical check is to separate optical sharpness from AF accuracy:

• Use a tripod and a fine-detail target.
• Test manual focus first to find the true sharpest point.
• Then repeat with autofocus and compare.
• A flat subject like a brick wall can also reveal whether focus is consistent across the frame.

If manual focus images are sharp but AF is consistently off, that points more to AF alignment. If nothing is very sharp, lens/body alignment or optical damage is more likely.