I don't understand. If you use aperture priority, how do you also set the shutter speed? Doesn't the camera just pick one to give you the correct exposure?
Roger that. The camera selected the 1/640 s. It also varied the ISO since I was using auto ISO - I use this a lot for ambient light pix. I set 1/500 s. as the minimum shutter speed and ISO 800 and 12800 as the, respectively, minimum and maximum ISO (in the auto ISO menu). Fixed at f/13 due to aperture priority. This is with a 1Dx, auto ISO functionality varies with camera model. If I run out of ISO, i.e. at 12800 and more exposure is needed then the camera will go to longer than 1/500 s. (this happens later in the day as well as when a cloud passes between the sun and the camera - the sun is weaker in Alaska at 60 degrees N compared to the tropics- so exposures may be different from you are used to).