Manual Mode on older cameras has always been a pain to use. It required a lot of forethought and button fiddling; then, if the light changed or you moved significantly, you had to do it all over again. While doing some playing with my Canon EOS 60D, I have discovered that Manual Mode is now really easy and relatively foolproof!
While walking around my yard after a rainstorm, I spied a big leaf on the ground that had some large water droplets. The sun was low in the sky, making some interesting shadows and specular highlights from the droplets. I knew that I wanted the droplets as well as the vein structure of the leaf to stand out, so I attached a macro extension tube to my trusty Sigma 18-200mm.
I had two challenges with this macro shot. The first was the very shallow depth of field, easily resolvable by stopping down to a small aperture. The second was that I was hand-holding the camera and wanted to avoid camera shake. When using the extension tubes, the old "shutter speed should be greater than 1/focal length" rule goes out the window. I use at least double this value and usually more.
Most of my shooting is done in Av (aperture-priority) mode so that I control the depth of field and let the camera choose the shutter speed. I also usually have the camera in Auto-ISO mode, so the camera can vary the ISO. I have found empirically that, with an aperture I set, the 60D then picks an ISO that gives a shutter speed of around 1.5 times the 1/focal length value.
For example, when I pick an aperture at a 100mm focal length, the camera sets the shutter speed to around 1/150 and picks an appropriate ISO. I am assuming that the approximately 1.5 multiplier accounts for the fact that the 60D is a crop sensor camera. Nonetheless, I knew that the camera-chosen shutter speed was not going to be fast enough to let me hand hold and get sharp images at this magnification. I was going to have to outsmart the camera!
Knowing that I wanted a shake-free image and good depth of field, I switched to Manual mode and selected a small aperture and fast shutter speed, fully expecting to have to continually tweak as the light and my composition changed. Much to my surprise, no matter how I moved and how the sinking sun changed the light, the exposure was spot on!
While shooting, I didn't give this pleasant coincidence much thought; the histogram looked good and I was able to keep the exact shutter speed and aperture I wanted. Only after the images were downloaded and being edited did I start to question how this worked. It seemed to me, with the changing light and changing composition, it would be impossible for a fixed aperture and shutter speed to always give "correct" exposure. I scratched my head for a while then realized the answer; shutter speed, aperture, and ISO together make up the exposure. It was the Auto-ISO mode that allowed the camera to vary something to get a correct exposure. As the ambient light decreased, the camera set a higher ISO; as my composition changed to include brighter subjects, the camera set a lower ISO.
Never having worked with a camera that had Auto-ISO, I didn't realize how powerful this feature is. I can now set the two most important exposure components to my liking for maximum creative control and still have the ability to shoot quickly in dynamically changing light conditions. With Auto-ISO turned on, I can choose how deep the depth of field is and whether the action is frozen or blurred, all without having to worry about exposure!
There are some caveats to this approach:
- Once in Manual mode, there is no Exposure Compensation; you have to use whatever exposure the camera chooses. If your subject requires exposure tweaking, you will either have to set a specific ISO or move to another mode.
- Non-professional cameras have a relatively narrow ISO range, which limits the range of aperture/shutter speed combinations. My 60D ranges from 100-6400; seven stops. This is not too bad though, considering many lenses have about this range also.
- The ISO can change drastically, depending on the light. Many purists want ISO as low as possible to avoid noise. My personal belief is that noise is the last thing you want to optimize for. Part of a good image is that it is sharp where it needs to be and has depth of field appropriate to the subject matter. If the image is noisy to satisfy these other characteristics, so be it; I can overlook noise in an otherwise compelling photograph. An out-of-focus or blurred image that is noiseless is much less interesting. Besides, noise reduction technology is getting better all the time. Noise that might be distracting today may be able to be removed next year.
Just like any other technique, this one has its plusses an minuses and is not applicable in all situations. Its just one more tool in your toolbox. Go out and give it a try; let me know how you fare!