What is one benefit of using a tank cover when processing films manually?

Using a tank cover during the manual processing of films serves primarily to avoid solution exposure to air and light. When developing photographic films, it is crucial to maintain the stability of the processing solutions. Exposure to air can lead to oxidation, which may compromise the quality of the chemicals used in the developing, fixing, and washing stages. Light exposure can also fog unexposed film, leading to a loss of image clarity and contrast.

By employing a tank cover, you effectively create a barrier that minimizes the films' contact with both air and light, thus preserving the integrity of the solution and ensuring the films are processed under optimal conditions for quality imaging. This practice is fundamental in maintaining both the longevity of the processing solutions and the overall quality of the final images.

In contrast, while improving image resolution, reducing processing time, and protecting the film from scratches are important aspects of film processing, these functions are not the primary benefit of using a tank cover. The tank cover specifically aims to shield the film from the detrimental effects of environmental factors, ensuring that the developing process achieves the desired results.