Single Lens Reflex, or SLR, cameras are what the pros use. They are sophisticated mechanisms capable of capturing the most minute details on the tiniest objects and then, with a quick change of lens, of bringing faraway images up close. The 35mm SLRs, both film and digital, give photographers almost complete control over how they choose to create their images. One of the most versatile and widely used cameras, SLRs come in both film and digital versions.