Teslong’s fixed focus probes are ideal for tight-access applications because they are so small in diameter - down to 0.153-inch (3.9mm). Teslong’s auto-focus lenses are larger in diameter - ½-inch (12.5mm), but the larger size gives them the benefit of an auto-focus system similar to one found in your mobile phone device. Fixed-focus lenses are optimized for focusing on objects that are ½ to 2-inch away, whereas the auto-focus lenses can focus on anything from ½ inch to 100 feet or even more.