Certified Professional Photographer Practice Exam 2025 – All-in-One Guide to Achieve Your CPP Success!

A film is considered "fast" when it is able to capture images effectively with less light exposure, and this characteristic can be attributed to the size of the silver halide crystals contained in the emulsion. In fast films, the silver halide crystals are indeed larger. The larger size allows these crystals to have a greater surface area, which increases the likelihood of interaction with light photons.

When light hits the emulsion, the larger crystals can react more readily, establishing an increased sensitivity to light. This higher sensitivity enables photographers to work in lower light conditions without needing an extended exposure time, making the film "fast." In contrast, slower films are composed of smaller crystals, which require more light to achieve the same level of exposure.

Denser, in this context, refers to the concentration of crystals but does not directly impact the speed in the way that crystal size does. Similarly, fewer crystals would not increase light sensitivity, and the size of the crystals is a more pivotal factor than density. Therefore, the correct understanding is that larger crystals are the key attribute that contributes to the speed of the film.