"So, let's pop our....onto a tripod and shoot. Hey, why do I see your.....drooping on that tilt-down shot? And did I notice the end of your lens vibrate a bit when you pressed the shutter release?...
Even when students come to class with a good tripod and head, they aren't always using it as securely as they should be. The bottom line is simple: if the......is moving when you shoot, you'll never resolve what the.....is capable of. Other factors enter into the picture, too. If you mount your .......on a decent tripod but hang a heavy lens off the front, you can actually get the center of gravity far enough out from the leg support that the front .......still moves a bit during exposure. And on many..... bodies, there's tangible "mirror slap" vibration that shows up....How do you tell if you've got a problem? Mount a longish lens on your tripod (a 70-200mm or similar will do). Frame a shot with the tripod head loosened. Tighten the head down. Did your shot move? If yes, then you've got a bad head. Did you see it move up/down/sideways in any fashion? If yes, then you've got a bad head and/or legs. Another possible test: lock the camera down. Pull down on the front of the lens slightly and release. It shouldn't move.....First they try handholding. Eventually, they realize that their results aren't as sharp as those of others.
So the next step is to work on improving technique. Elbows get tucked, the ..... is braced against stable objects, they stop holding their breath, etc. But that doesn't solve every problem or work in every situation. And it certainly doesn't always work for very long lenses. "