Light wave dynamics and blurred images – Shutter Speed #4
We’ll stay with the bicycle subject matter for at least one more day. At least long enough to add a little more knowledge to shooting blurred images with wide angle lenses.
Yesterday’s photo discussed subject mater moving laterally to the shutter plane. The result can be quite striking with the pincushion effect created by rotating the camera around a central vertical axis as the subject travels past.
It’s difficult to keep much in focus shooting with a wide-angle lens on laterally moving subjects.
Shooting a subject moving toward you or away from you requires a different set of skills and a much different result.
Today’s photo was shot with one hand on my bicycle handlebars and the other grasping a Nikon D330 while trying to balance and compose with a narrowed view through the camera viewfinder.
Shot at 1/20th of a second at f16, the blurring is sufficient to show motion of the young rider. It is not so slow that it blurs all his surroundings.
The heaviest blurring happens in the foreground with what appears to little, if any, in the distance. In reality, the blurring is exactly the same degree of movement for both distances. The camera traveled the same distance for the same period of time for both foreground and background. Yet the foreground is more blurred.
The difference in what we see is related to the Doppler Effect, more generally applied to sounds and radio waves than to photographic subjects. Yet it is the same principle, where the camera records the change in frequency of light waves, not sound waves.
Check the Wikipedia reference for Doppler Effect for an understanding of how the frequency of sound waves are modified by movement of the emitter and the receiver.
In our case, the frequency of objects in the foreground are stretched, elongated filling a lower frequency during exposure. Objects in the distance stay closer to their original frequency so they aren’t as blurred.
Foreground objects travel a further distance over the same period of time as the background objects. Their frequency, the number of times the light rays they reflect is greater so they are stretched, appearing in a longer path.
The distance objects travel the same distance but their wave relationship to the shutter plane is not changed. They appear to not move because their light rays are almost always reflected from the same spot.
Referencing the Doppler Effect is a useful tool as you consider how best to use blurring to communicate the story of your photo. Consider the physics of light waves as just another tool in the camera bag.
Did you ever think you’d need to understand wave dynamics to be a better photographer?
