April 4th, 2015
Continuing our discussion of exposure, I would next like to move to another aspect of the exposure triangle, shutter speed. When the "shutter" button on a DSLR is actuated, the mirror reflecting light up to the viewfinder snaps shut, and the shutter opens for a period of time. This period of time can be very long (unlimited time in "bulb" mode), or very short. For instance, on many of the mid to pro level Canon DSLRs, like the 7D Mark II and 5D Mark III, the minimum shutter speed is just 1/8000th of a second. For a visual of this process, the Gavin and Dan over at Slo Mo Guys put this one together.
Shutter speed is a tricky one, and can ruin a lot of shots if you don't pay attention to it. That's because high shutter speeds reduce motion blur, but require much more light. Except in certain circumstances where you purposely want blurred motion, where you want the appearance of fast movement (or for light painting), it would be great to always be able to use a super fast shutter speed. Unfortunately though, that's rarely the case.
Say you want to keep your ISO down (our next discussion on exposure), or you want a narrower aperture to widen up your depth of field. In either of these circumstances, you have to make judgement calls. Maybe in bright sunlight with a high performing full frame DSLR you can get away with using f/8.0 at ISO 100 with a 1/1000s shutter speed, but how often are our light levels that forgiving? No, more often I find myself in a dark place, like the back of an ambulance, or indoor sporting event, where my fast moving subjects require fast shutter speeds. This forces me to use the maximum (or maybe a stop below) aperture, and a high ISO (which introduces noise). Image stabilization (IS) is a great lens addition, but only reduces camera shake, not motion blur from subjects.
This is why it is important to understand which shutter speeds to use in individual circumstances. At an absolute minimum, without using a tripod or IS, stationary subjects get a 1/focal length + 1/2 stop shutter speed. For instance, with a 100mm lens, I wouldn't go below 1/125s. With IS, you can further reduce shutter speed by the number of stops the lens IS system compensates for.
Moving subjects get 1/500s, and fast moving subjects 1/1000s or above. Slower shutter speeds can be used with caution, assuming you can follow the movement, and take the photo when the subject has slowed down or stopped for a second or two. In these situations, I often take quite a lot of photos in succession, just to make sure one is without significant motion blur. This practice can be frustrating though, so patience is key.
There are certain circumstances where motion blur is wanted, though. In landscape photography, slow shutter speeds smooth moving water and clouds, and allow for the use of narrow apertures. In some of my EMS photography, different providers may be slightly blurred to bring forth a sense of speed and urgency inherent to the practice of emergency medicine.
Thoughts about shutter speed? Take a moment to leave your thoughts in the comment section below.
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