Recently after reading in-depth reviews about each of my "Landscape Lenses" that I currently own; the Pentax 12-24 F4 and the Pentax 16-50 F2.8, I've been extremely religious in shooting the 12-24 at f5.6-8 and the 16-50 at f5.6 for 99% of what I shoot with those lenses. The reason being, that this is the consensus on the optimal range of aperture for the highest IQ that those lenses have to offer based on the multiple reviews that I've read for each of them. If you happen to do a lot of telephoto Work you will Definitely understand the more drastic effect/relationship between your f-stops at various focal ranges when you factor in perspective. Because both of my telephoto zooms are Macro lenses, I often make it a habit to shoot those lenses at higher f-stops to avoid forgetting to shift them from say f5.6~8 when I shoot a subject that's 20-30 feet away versus shifting to f13 with a portrait shot that's 4-6 feet away. Also, (-) minus the use of a flash, which I shoot in full Manual Mode, I always shoot my cameras in Aperture Priority Mode. When I want to shoot something, it is the best starting point that determines how the image is going to look minus composure and perspective. It initially tells me if that f-stop is going to work with my depth of field scheme that I want to achieve. If need be, I can then quickly hit the direct ISO button on my K-7 and especially my K-5 to increase the ISO if my shutter speed isn't high enough in the Metering for that shot. Yes, I definitely had that aperture set for that Gull shot ahead of time and knew that it was necessary to have the aperture at precisely that f-stop to get all of that bird in focus and achieve the depth of field scheme that I wanted for that shot at 300mm(.) You've got to understand that if you shoot something like a 16-50mm lens at f13 at say 10ft and fill the frame the same as if you shot it with a 70-300mm lens at f13 and say 30 feet and fill the frame the same, the telephoto lens will have about 2-3ft in-focus depth of field where as your general purpose zoom will have one that's about 10ft of in-focus depth of field. If I recall correctly the Gull was about 20-30 ft from me in this shot and the rocks behind it where between 5-10 feet from the Gull. You can clearly see that the depth of field falls off between the Birds tip of the left wing and the Rocks behind it. Don't tell me that f13 yields a handicap on the focus ability for this shot--that's retarded man given this perspective and depth of field characteristics of this lens at that focal length. I was on the money with this shot when it came to getting the Bird in focus and getting this shot how it looks. Any higher f-stop, you blur the water and rocks too much. Any less f-stop, you jeopardize the ability to ensure that the Bird's 2 ft distance from Wing to Wing is in complete sharp focus.
