In a scenario where you were say, shooting a dog that was jumping obstacles, would you prefer to shoot in Shutter Priority, Aperture Priority, or would you dial in your exposure previous to the jump in Manual, and shoot freely, knowing your shots are going to be consistent?
If the lighting conditions weren't changing, and I was just sitting there as dog after dog came by, I would absolutely use M and check the histogram to tell me how the exposure was.
However, if the lighting conditions were continually changing etc. then why not use the TV. Getting the shot at all is better than not getting the shot because you're fiddling with the buttons.
Nate, the scenario you set forth, with a dog, or say a human high jumper, jumping an obstacle is a good one. One reason NOT to use a Tv or as other makers call it, Shutter Priority automatic setting, is that if the light level is constantly changing, so will be the f/stop one is given.
Outdoors in the spring time, with a jumping event like high jump, the photographer using Aperture Priority Aurtomatic picks an ISO setting, let's say ISO 800, so that he can get a wide aperture, let's say f/3.5, and a high shutter speed like 1/2000 second. F/3.5 with a 200 to 300mm lens will provide a limited depth of field, effectively blurring the background on each and every frame shot. The shutter speed will always be the fastest it can be, given the f/stop selected. If the sun peeks out from behind a cloud, the shutter speed might go up to 1/6000 second. If a dark rain cloud passes by the sun, the shutter speed might drop to 1/1200 second. In any and all cases, the background will be blurred by the pre-selected aperture. If the camera were in Time Value, the lens would yo-yo the aperture smaller whenever the sun peeks out, often greatly increasing the depth of field and bringing the background more into focus.
The danger in Tv shooting comes when one "runs out of f/stop" to use the old expression. In Time Value, if you pick a Time that is very fast, let's say 1/2000 second, and your subject runs from the bright part of the course into the shade, your lens might not have a wide-enough maximum aperture; the system will decide to lower the shutter speed so far that blurred photos will result. In action photography,with a long lens like a 300mm lens, combined with a moving subject, the real priority is controlling the focus for proper depth of field to keep the background under control, and making the proper "picture". If the camera is in Time Value mode and the light level drops substantially, or the subject moves from a bright area to a darker area, the camera can easily be required to drop the shutter speed into the range where you "run out of f/stop". If you have your lens wide-open on a cloudy day at let's say f/4, you are fine in the sun as long as the ISO is high enough. If the light level drops, the TV will have no additional wider aperture to select, and it will "run out of f/stop",and the shutter speed will be forced to drop--often to the point of blurring the subjects' movements.
This is why Nikon came up with the Auto ISO setting that Canon refused to implement for so long...in situations like track and field, where many running events have action that alternates between open sunlight and deep shade created by a huge stadium's shadow, it is advisable to set a wide aperture and allow the camera to adjust the shutter speed on the fly. Without AUTO ISO, using a TV or SHutter-Priority setting, the photographer's a camera might mess up the exposures pretty badly as the action goes from in the sun to the shaded parts. On the 200 meters for example, there are four to five seconds where the runners are in sunlight, and then for the remaining part of the race, the runners are in the shadow of the stadium. Same with the 100, and the end of the 400 and 800 meters. Aperture Priority automatic is the mode where the photographer will not be fumbling with settings....Time Value is very,very risky unless the lighting is fairly steady and/or the camera has an AUTO ISO mode where the ISO will shift on the fly to compensate for the "loss of f/stop". So, basically, most shooters will probably go for Aperture Priority Auto when shooting most sports events, knowing that a large,wide aperture will ALWAYS provide a constant Depth of field/background control and will always provide the fastest shutter speed possible, given the prevailing lighting conditions. Even if the subject moves through a course where there are sunlighted and shaded parts.
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