There is interest among many photographers in what are known as “fast” lenses. Fast lenses have large maximum apertures (from approximately f/1.0 to f/2.0) that provide a shallow depth of field (enabling out of focus backgrounds, aka “bokeh”) and excellent low light performance for working handheld.

I'm generalizing here, but more often than not, landscape photographers use small apertures (f/8-f/22) to create a large depth of field for maintaining sharp focus from the immediate foreground all the way to infinity (see image at right). They also often work on tripods to facilitate using live view for precise focus and framing, and to enable longer exposures for capturing cloud and water movement. Consequently, landscape photographers rarely have a need for the large apertures found in fast lenses.

Canon makes a line of pro quality "L Series" lenses with a relatively slow maximum aperture of f/4. My kit consists of the EF 17-40mm f/4 L, EF 24-105mm f/4 L, and the EF 70-200mm f/4 L. People often ask why I prefer these relatively slow lenses. The reasons mostly relate to size and cost. Because fast lenses are larger in diameter (and consequently require larger glass elements), they are both heavier and more expensive than their “slower” equivalents. The weight in particular is an issue for us "over 50" landscape photographers who do a lot of walking. I prefer these slower lenses because they're smaller, lighter, and less expensive than their faster counterparts, while still providing the clarity required for landscape work.