Pros love their fast glass. Maybe they're onto something.
By Mike Stensvold
There’s Something To Be Said For Slower Lenses Slower lenses are smaller, lighter and much less costly than faster lenses of equal focal length, making it possible for many more photographers to access longer focal lengths. Slower lenses also generally take smaller-diameter filters, which saves you money if you use a lot of filters.
With a slower lens, however, the viewfinder image will be dimmer, making composition and manual focusing more difficult. Autofocusing will be slower (and with some SLRs, not possible), and you’ll have to use a slower shutter speed or higher ISO in any given light level.
Bottom Line When budget and logistics permit, faster lenses can give you better photos because they let you use lower ISOs for better image quality, provide faster autofocusing performance and let you use faster shutter speeds in a given light level. When fast lenses are too costly or bulky, slower lenses allow you to obtain focal lengths you couldn’t have otherwise. But for those whose living or reputation depends on image quality, faster lenses are well worth the cost.