Final answer:
The optimal temperature for a developer solution in manual film processing is approximately 68°F or 20°C, which ensures a good balance for image development.
Step-by-step explanation:
The optimal temperature for the developer solution in manual film processing is typically around 68°F (20°C). This temperature is considered a standard for developing black and white film as it provides a good balance between developing time and image quality. Using temperatures that are too high or too low can affect the development process and the resulting images. For instance, higher temperatures may lead to overdevelopment, while lower ones may result in underdevelopment. It is important to maintain the developer temperature consistent to ensure predictable results.