The f-stop system is a combination of camera bag and camera bag insert. We sell five different camera packs and backpacks in our Mountain series and another three in our Ultra-Light series. Each of these bags requires a camera bag insert, and we have seven inserts that work with various bags, packs and backpacks. The camera pack selector helps you discover the best camera pack or camera bag, and helps you match the best camera bag insert to meet your needs. Just answer a few questions to find the perfect fit - it usually takes 2-3 minutes!