The yellow bump on the Pentax lens.

The yellow bump on the Pentax lens is the focal length mark or focus. It is usually used to help photographers focus, especially when using manual focus mode. The photographer can rotate the lens according to the shooting distance and the required depth of focus, so as to focus on the yellow bump and ensure that the subject is clearly focused. This yellow bump is usually marked on the lens together with other focus indicators so that users can find and use it more easily.