How Auto-Focus Affects Shutter Speed

I’ve always heard lenses being categorized as either fast or slow, with the contributing factor being maximum aperture which is how much the lens can open. The more light the lens can let in, the better. I always associated the relationship between aperture and speed with shutter speed. The more light the lens lets in, the greater the shutter speed, which in low-light situations, means you have a greater opportunity to take photos without motion blur. I’d never realized how aperture contributed to auto-focus speed until I got my first slow lens, the RF 100-400 f/5.6-8. Since I started taking pictures of birds, the thing I’ve struggled with the most has been getting them in focus. Before the RF 100-400, my main lens had a constant f/4 throughout the focal length, and I’ve always had f/1.4, f/1.8 or f/2.8 lenses before that. Auto-focus had never been an issue before and I couldn’t figure out what I’d been doing wrong. That was until I was watching a bird photographer on YouTube talk…