dcampbell52 Loc: Clearwater Fl

Good question. For me, it depends on the shot and what I'm trying to accomplish. If I want a shot with a lot of depth of field, I try to keep my aperture high and adjust my shutter speed or ISO to compensate. If I want a tight focus and want to drop the foreground and background out of focus then I go for a more wide open aperture and then can compensate the other way with shutter speed and/or ISO. Generally, I try to keep my ISO below 500 in general. However, I always keep the type of lens that I'm using in mind. My Nikkor 50mm lens is a 1.4 so it has sharper or narrower field of focus at the wider open apertures (I tend to use it as a portrait lens on my DX7100 or a general (and sometimes portrait on the D610). My Nikkor 80-400mm lens has a f/4.5 to f/32 aperture and so I have to adjust my ISO up in low light or slow the shutter speed down. My Tamron 10-18mm is similarly constrained by a 3.5-4.5 wide open aperture so it can also be a slower lens in low light and I have to watch my ISO and / or shutter speed when making decisions on focal depth. (As, I'm sure you know Rongnongno) almost all lens choices are a case of choosing your poison as far as DOF/Aperture/and Speed. If you are shooting sports you have to make choices (depending on available light) of ISO and shutter speed to compensate for available aperture for needed depth of field.
The good (or nice) thing about digital photography is that many of these choices can be made from photo to photo and on the fly, where in the film days, you had to decide based on film speed (ASA 100, ASA 400, Color, or B&W, Slide or negative/print). Now, with digital, the choices can be made from photo to photo (if you want). I almost never use auto mode on my camera, I prefer Manual, Aperture Priority, or Shutter Priority, about 95% of the time and only use Auto (or program) the other 5%. But that's just me... The wife shoots auto about 99% of the time with her D70s (mainly because she doesn't understand and doesn't want to learn aperture/shutter speed/depth of field) but she sure complains when the shot is out of focus or blurred by subject speed being to fast for the exposure and or knowing when to use the popup flash or add on the SB800 or SB910 flashes. Having said all of that, she does fairly well and gets some really nice shots.

Julian Loc: Sarasota, FL

Perhaps, equation?

jmvaugh Loc: Albuquerque

As an amateur and still reading and learning, I like Aperature Priority for most of my landscape shots. I pick the aperature and the ISO and the camera picks the shutter speed. If the light is rapidly changing and my shutter speed frequently dips down where I can’t hand hold it, I’ll then set it on Auto ISO. The mass ascension at the Balloon Fiesta was a good example. The pre-dawn hint of light to the east and the Dawn Patrol doing short blasts of propane lighting up the first balloons was really challenging....but I didn’t revert to full Auto or “P” and got some decent shots for my eyes. Definitely not up for critical review but I’m happy with my slow progress.

Largobob

I believe that aperature CAN affect sharpnes. While aperature certainly affects depth of field and exposure (available light striking the sensor), there are physical phenomenon like dispersion and diffraction which cause light to bend around corners of objects....similar to how waves bend around a breakwater in the ocean. Light travels in straight lines in all directions from the source (both reflected light and emitted light). But, if you research "single slit or double slit experiment" you will see how secondary wavefronts are formed as light passes through a narrow opening.....helping support the theory that light has wave properties. There is a whole branch of physics devoted to studying this. So: if one stops-down (smaller apperature) too much, dispersion around the aperature will cause dispersion/diffraction....which will be seen in the image as "unsharp." I also feel that every lense, no matter the manufacturer or cost, has a "sweet spot".....a combination of focal distance, magnification, and aperature where the image will be at its best. Changing any of these CAN effect apparent sharpness of the image produced.

Largobob

Sure is hard to argue with measured data.... LOL