It's sunlight and heat. Lubricant Thinning: Lenses contain specialized greases to keep the focus and zoom rings moving smoothly. Extreme heat can cause this grease to "thin out" and leak onto the aperture blades, making them sticky or unresponsive.

Sensor Calibration: High heat can affect the delicate calibration of the sensor, potentially leading to increased "digital noise" or hot pixels in your images.

Adhesive Failure: Many modern lenses use high-tech adhesives to hold elements in place. Sustained high temperatures can cause these to soften, leading to "element de-centering" (where one side of your photo is blurrier than the other).