I was so thrilled to get my first telephoto lens; it was a Nikon 70-300mm, and I was poised to take all of these beautiful, up-close images! Well unfortunately, things didn't work out as planned; instead of being sharp, most of my images were blurry, and instead of being bright, many of my images were underexposed. So here are a couple of thoughts as you take that new lens you just got outdoors to photograph animals or scenery at the park. The most common mistake we make with these long lenses is that we don't use a fast enough shutter speed which is critical no matter if your subject is moving or stationary. You see, with a long lens, the photographer is much more likely to introduce "motion blur" by moving the camera, when hand-holding it and snapping the shot. The rule of thumb to lesson this problem is to take your focal distance (say 200 mm) and then dial in a shutter speed that's the reciprocal of that measurement, (i.e., 1/200th of a second) and don't let the camera fall below that speed. Of course, shooting on a secured tripod removes this obstacle, but I often like to run and gun, taking a brisk walk in the park, while also stopping to photograph waterfowl, squirrels and the occasional white-tailed deer. My compromise is a monopod, which allows me a much better brace when snapping the shutter. I can even improve upon its use, by securing the monopod to a branch or post with a wire tie and using my self-timer to trip the shutter.
Dialing in that fast shutter forces us to compensate by increasing ISO and/or selecting a larger lens aperture for a well exposed image. More often than not, if shots are presenting themselves quickly and unpredictably in the woods, I am going to choose to increase my ISO rather than selecting an overly large lens opening. The reason is simple, my priority in this situation is an in-focus shot, and a smaller lens opening gives me greater depth of field and therefore a greater margin for error if I misfocus slightly.