With shutter speed increased to freeze motion, the aperture must be larger (a smaller f-stop) to let in enough light.
For the last couple of columns we have been discussing how your camera is able to control light to expose the photograph you are taking. This control revolves around the interplay between the Aperture and Shutter Speed, and understanding this relationship is essential to a basic understanding of the photographic process.
In the last, May, column I published a photo of my friend speeding by in his boat that was to be given to his family up North. The good news was the exposure was perfect; just the right amount of light to see everything clearly. The bad news is what we wanted to see clearly, my friend in his boat, came out very blurry. It was dusk, meaning not much daylight, and my friend was near full throttle speeding by, and this creates difficult photo taking circumstances. So where did I go wrong, and could I have succeeded in getting a good photograph?
Looking at my camera settings I noticed my ‘shutter speed’ setting was 1/15 of a second and the aperture-f/stop was set at f/8 aperture f/stop, and that’s what the available daylight would allow for a good exposure. But at that shutter speed it is very difficult to ‘freeze’ motion and to get a clear non-blurry shot of a fast moving boat, especially one moving across your field of view. This is what the shutter controls – light and motion, as the aperture controls light and depth (of field or what stays in focus from close to far distance).
There is no depth of field issue with this photograph. All I want to have in focus (sharp) is my friend in his boat, therefore as long as I pre-focus on the right distance any f/stop will do, and the lowest number – widest – most open setting is what we may need in this case. This adjustment of the aperture f/stop will give us flexibility to adjust the shutter speed to stop motion, which is the issue with this shot.
Here’s the solution to getting the shot right, that is, stopping motion to have a clear shot of a speeding boat at dusk with low daylight conditions. This is the thought process to follow: For the well exposed blurry boat photograph I had the aperture set at f/8, which provided more depth of field than I really need. My camera is capable of stopping down (opening up) to f/2.8. I had a shutter set at 1/15 (of a second) that is too slow to ‘freeze’ a fast moving object. I need a faster shutter speed. If I open the aperture from f/8 (past f/5.6, past f/4) to 2.8 I will gain 3 full f/stops. Since each ‘stop’ doubles the amount of light reaching the chip I have to compensate adjusting the ‘shutter speed’ to get the proper exposure. To that end I increase the shutter speed 3 stops, that is from 1/15 (past 1/30 and 1/60) to 1/125. That’s right, in terms of proper exposure 1/15 at f/8 = 1/125 at f/2.8 they are the same, but this change to the latter setting also greatly improves my cameras ability to stop motion for a non-blurry result; the faster the setting the greater this ability. The boat will be clearer to see, more frozen in space, and there will be less depth of field in front and behind the boat. But, in this case I wanted to see the boat, so if I focused well on the boat, I do not care about the depth of field.
When you bring your camera to your eye, first take a look to evaluate and set the light reading for a proper exposure. To see your camera f/stop and shutter speed settings you can be in Av (aperture preferred), Tv (shutter preferred, or M (manual mode). [Using any other settings such as the graphic “scenic” symbol modes means shooting blind, using the luck of the draw, hoping for the right result. At times when I really have to grab a shot real fast I’ll most often dial to the “P” (program) mode.] After having the right exposure, determine your objective and adjust the aperture and shutter accordingly, keeping the proper exposure. With practice the process will develop quickly, and you’ll know just by looking at the scene what you would like to do before lifting your camera.….. until next time, permission to come ashore. Send me your questions to possibly cover in next issue