What is the difference between a F1.8 lens and a F5.6 lens? It's really very simple! F8.1 has a much larger lens, and therefore it allows more light to pass through. There are several benefits in having a larger lens. Number one: The quality of the background is improved. Number two: Your focus speed is faster. Number three: Low light ability is better. F1.8 lens are a professional level. F5.6 lens are the commercial kind. For a higher quality photo, you might consider using a larger size lens.