If a screen is dirty the camera/lens if working in auto-focus mode will try and near focus on specs of dirt. The camera will try and fight that as clearly you are trying to view further than a few centimetres.
The tiny lens drive motors are not designed to keep working 24/7 and this will have an impact on their MTBF.
Having a clean screen will prevent this.
Categories:
CCTV Washer Series - General,
WA-10-S,
WA-25-S,
WA-5-S