Use a controlled, repeatable setup so you’re testing the lens rather than vibration or focus error. Mount the camera on a sturdy tripod on a solid surface, aim at a proper lens test chart, and eliminate vibration with mirror lock-up/delay and a cable release or remote if available. Keep ISO constant and test the lens at several apertures, since most lenses are not sharpest wide open and have a “sweet spot.”

To check autofocus calibration separately, use a focus test target such as an angled ruler or a downloadable focus chart. Focus on a marked point, then inspect the image to see whether the sharpest point falls where intended or in front of/behind it. If it does, the issue may be front- or back-focus rather than optical sharpness.

A practical workflow is:

1. Stabilize camera and scene.
2. Shoot a sharpness chart at multiple apertures.
3. Review images carefully for center and overall sharpness.
4. Run a separate front/back-focus test.

If autofocus is consistently off, some cameras let you apply per-lens AF fine-tuning. If the lens is sharp under controlled conditions, any softness in normal shooting is more likely due to technique or focus accuracy than a defective lens.