Likely causes
- Dome or glass cover scratched or dirty
- Protective film left on the lens
- Condensation behind the lens cover
- Subject closer than the minimum focus distance
- Dirty housing reducing contrast
Quick checks
- Clean the lens cover with a microfibre cloth
- Check for a protective film
- Look for condensation inside the housing
- Test focus at different distances
Step-by-step fix
Clean the lens and housing
Remove any transit film
Let the camera dry if condensation is present and check the seal
Reposition the camera to suit the subject distance
Compare with a second camera before replacing