|A running sable antelope in Botswana was captured by panning a Canon EOS-1D Mark IV with a 100-400mm ƒ/4.5-5.6L set to 210mm. The shutter speed was 1/350 sec. at ƒ/4.5 and ISO 800. A wide-open aperture gave enough depth of field to render the head of the animal sharp, and the 800 ISO enabled a faster shutter speed in the overcast conditions. It all worked together to stop the animal's action.|
Q I will just never quite get apertures; in the May 2011 issue of OP, your colleague Ralph Hopkins talks about shooting from ships using varying apertures at a distance depending on lenses, etc. I just cannot interface apertures used for light vs. focus.
A The aperture setting is critical to three different aspects of image capture. The first is to control the amount of light that's allowed through the lens. The smaller the ƒ-stop number, the larger the lens opening; ƒ/1.4 is wide open and ƒ/16 is very small. Ideally, the aperture will allow enough light so that the image will be rendered with the proper tonal properties; that is, there's detail in the highlights, as well as information in the shadows. Too much light, and the image is "blown out"—too bright. Too little light, and the image holds deep, indiscernible shadows—too dark. High-contrast scenes (those with both very bright and very dark areas) may be outside the normal possibilities of film or sensors.
Second, the size of the aperture also dictates the size of the area of the image that can be rendered in sharp focus by a particular lens; that is, the depth of field. Large apertures (e.g., ƒ/1.4, ƒ/2.8, ƒ/3.5) render a smaller depth of field than small apertures (e.g., ƒ/11 and ƒ/16). So as we stop a lens down (that is, decrease the size of the opening), we increase the area of relative sharpness (depth of field). The depth of field is doubled by every two-stop decrease in aperture.
The problem, of course, is that by increasing the depth of field, we're also decreasing the amount of light that passes through the lens, and this is the "light vs. focus" concept that you're trying to grasp. Serious photographers are always weighing the need for depth of field vs. attaining more light (for faster shutter speeds); each image is a compromise of sorts. The alternative is to leave your camera set on "P for Perfect," in which case the camera can make every decision for itself without considering what you're trying to accomplish.
So say you're using a telephoto lens to photograph a running deer. If you wish to stop the action, you'll choose a large lens opening to let in plenty of light so that a fast shutter speed can be employed. Stopping the animal in mid-stride is more critical in this case than the depth of field; as long as the animal is sharp, you don't care if the background goes out of focus.
But if you're photographing a landscape with interesting rocks or flowers in the foreground and mountains in the background, you would use a small aperture to gain maximum depth of field (from close in front of you into the distance) and compensate for the loss of light with a longer shutter speed.
The third aspect of aperture is its impact on the sharpness that a lens can render. Obviously, lens sharpness varies depending on the quality and construction of the optic. But generally, any lens isn't as sharp at its widest aperture as it will be when stopped down two to three stops. At the other end of the range, a lens stopped down too far (ƒ/22, ƒ/32) will lose sharpness due to diffraction.
In summary, the photographer needs to have an idea of how much depth of field is needed to cover the subject and achieve the best composition, where the best sharpness of any particular lens is, and what aperture will still give the correct exposure. These variables are combined with shutter speeds (time of exposure) and ISO settings (sensitivity of the sensor) to achieve the best possible rendering under varying conditions. The very best way to become comfortable with these principles is to practice various combinations with a variety of subjects, and carefully observe the results they give you until the choices become instinctive.
For an excellent tutorial on the relationships between depth of field and aperture settings, see www.cambridgeincolour.com/tutorials/depth-of-field.htm.
An Eagle-Eyed Reader
Q In the June 2012 issue of OP, you published a photograph of a bald eagle taken at 2912mm using a Canon EOS-1D Mark IV (1.3X crop factor), EF 800mm f/5.6L lens and EF 2X and EF 1.4X tele-extenders. You indicated your exposure was 1/1000 at f/16 with ISO 400. The sunny-day rule (f/16 rule) indicates that in full sun, which it looks like the eagle is, the ISO would be the equivalent of the shutter speed at f/16. Was there a misprint, or am I missing something?
A Good catch! The correct ISO for the eagle image featured with the column was 1600, not 400. The Sunny 16 rule, which is a standard basic exposure for film, still has merit with digital capture, although we have more control now. In this situation, the 1000 ISO that the rule suggests offered insufficient light on the subject, as was demonstrated on the histogram of a previous exposure; I therefore manually selected 1600 ISO for a better result.
Photographers in the digital age should make good use of expanded ISO for exposure control. While higher-speed films were (are) available for use in low-light situations for film photographers, the resulting loss of quality (graininess and noise) is far from acceptable. Now, each new generation of digital camera offers increasing capability for expanded ISOs with excellent results. Manipulating the capture ISO is no longer a last-ditch effort to save the day; it has become a critical third factor in calculating exposure—as important as choosing the shutter speed and aperture.
There are a number of ways to arrive at the optimal exposure settings for any given photographic situation, but because ISO does have quality implications, I tend to first determine the optimal shutter speed and aperture setting and then adjust the ISO to enable them, keeping in mind that there are upper limits. For example, when photographing flying birds, I choose a shutter speed to stop the action, an aperture for needed depth of field and then adjust the ISO until the shutter speed/aperture combination is achieved. Many DSLRs can make the ISO adjustment automatically, calculating the ISO needed to capture under the prevailing light conditions, shutter speed and aperture settings. But you can still override these settings to fine-tune the exposure based on the results you're getting.
Calibrating The Color Of An iPad
I recently upgraded to the "new" Apple iPad. As I've mentioned before, it's a great tool for photographers. I love the high-resolution screen and faster processing speeds. But the exaggerated color rendered by the HD screen bothers me. I don't know if garish is the new normal, but I don't care for it because it gives my portfolio images a false, over-saturated look.
At a recent photo seminar, I saw Hector Martinez of Datacolor (makers of Spyders and other color-calibration tools) demonstrate how to view color-correct images on an iPad. There's an app for it, naturally. You start by downloading a free app from iTunes called SpyderGallery; the application creates a safe, color-calibrated space where you can view your image portfolios without unwanted enhancement.
The tricky part is that you do have to perform the color calibration yourself using one of Datacolor's Series 4 Spyders plugged into the USB of either a laptop or desktop computer. You place the Spyder on the iPad and start the app's setup. The iPad goes through a calibration process, showing the Spyder red, green and blue colors, and a series of gray tones. Once the calibration is completed, you use the SpyderGALLERY app on the iPad to display your portfolio with the correct colors. There's a slider at the bottom of the app's viewing screen that allows you to turn the corrected color off and on to see the difference, and it's significant. If you don't already have a Spyder, you should. It's very handy for its original purpose of calibrating your monitors so they display color accurately—something you should be doing on a regular basis if you're serious about photography.
Speed Up Your Laptop
If your laptop computer is sluggish or the hard drive is full, a potential answer is the new replacement solid-state hybrid drive from Seagate, the Momentus XT. I just changed out the drive in my MacBook Pro with the 750 GB version, and it sure beats replacing the whole laptop! The Momentus offers the fast access of solid state and the high capacity of a standard hard drive spinning at 7200 rpm, and it brings the laptop much closer to the capability of the desktop in handling large files in complex software programs, such as Photoshop and Lightroom. Get all the information about the Seagate Momentus XT at www.seagate.com.
For information about upcoming seminars and digital-imaging workshops, visit www.georgelepp.com. If you have any tips or questions, address them to: OUTDOOR PHOTOGRAPHER, Dept. TT, George Lepp, 12121 Wilshire Blvd., Suite 1200, Los Angeles, CA 90025-1176 or online at www.georgelepp.com.