Final answer:
The term used when placing the dot towards the operator in film mounting is called labial mounting. The identification dot helps in determining the film's orientation for correct viewing. In some optical applications like telescopes, a third lens may be used to correct an inverted image for proper viewing.
Step-by-step explanation:
When mounting films in a radiographic or dental context, the term used when placing the dot towards the operator is called labial mounting. The dot, also referred to as the identification dot, is a marker used to determine the orientation of the film. In labial mounting, the convex side of the dot faces the operator, which ensures that the anatomical structures are viewed as if the operator is looking directly into the patient's mouth. This method aligns with the universal standards for dental film mounting.
The minus sign in the context of magnification typically indicates that the image produced is inverted. This inversion is not an issue when observing celestial bodies, as in the case of telescopes for astronomy. However, for terrestrial applications such as telescopic gun sights or navigation devices on ships, an inverted image is problematic. To correct this, additional lens mechanisms such as using a third convex lens or adjusting the eyepiece position can be employed to create an upright image, effectively inverting it a second time to be correctly oriented for the observer.