Today’s Question: I saw your (very nice) photo of a crop duster, and wonder how you go about making sure the propeller is actually shown to be moving rather than being “frozen” by a fast shutter speed. Do you just stop the lens down to the smallest aperture?
Tim’s Quick Answer: Photographing propeller-driven aircraft is a perfect example of a rare case when I will actually use shutter priority (or time value) exposure mode. I determine an appropriate shutter speed for the subject, and set that as a fixed exposure setting in shutter priority mode, ensuring a degree of blur for the propeller in each photo.
More Detail: In the case of the photo you are referring to, the crop duster is powered by a turboprop engine that turns the propeller at a relative fast rate. Therefore, a shutter speed of no faster than about 1/250th of a second or so will ensure a small amount of motion blur for the propeller, while still providing a shutter speed that is fast enough to help achieve a photo where the airplane actually appears sharp.
For those who didn’t see the photo referenced in the question, by the way, you can view it on my 500px page here:
When you are using shutter priority mode (as opposed to aperture priority mode) there is an increased risk of “running out” of appropriate exposure settings. In other words, there is a risk that the shutter speed you have set will require an aperture that goes beyond what your lens can actually achieve. On a bright sunny day that might mean even with the lens fully stopped down the exposure is too bright, or that even with the aperture fully open the exposure is too dark.
Because of this issue, when I set the camera to shutter priority mode I will hold the shutter release button halfway down to enable the meter on the camera, and then point the lens at various areas within the scene before me, being sure to check the brightest and darkest areas to confirm that an appropriate aperture is available.
If the subject will remain under relatively fixed lighting conditions, I might also use the manual exposure mode with specific exposure settings that work for the subject. However, when photographing aircraft it is very likely that the lighting conditions will change on the subject. For example, in some cases the aircraft may be lit from the front, while in other cases it may be backlit. In these types of situations I find that shutter priority mode helps ensure more consistent results, though it may also be necessary to apply some degree of exposure compensation.
Again, the key to photographing propeller-driven aircraft is to use the fastest shutter speed you can (generally speaking) that will still ensure at least some degree of motion blur for the propeller. The specific shutter speed will vary based on the rate at which the propeller is spinning, but in most cases shutter speeds in a range from about 1/125th of a second to about 1/350th of a second will produce excellent results.