We’ve probably all seen a very attractive portrait photo where the eyes and face of the subject are perfectly in focus and everything in the background is blurred out of focus. Or maybe a landscape photo where everything, from close to the camera to the most distant objects, are perfectly in focus. Or, how about a nighttime photo that shows a subject in the foreground with stars arcing through part of their polar orbit. A professional photographer will set the ISO, f-stop and lens speed on his camera differently to take these three very different photos.
Most digital cameras available today come with a number of automatic settings; these settings copy camera functions for some common types of photos situations . The auto settings are usually represented by little icon figures displayed on a dial that the user turns to make the selection. [Illustration 004-1] We’ll get back to the auto settings in future articles, but first some technical stuff you’ll need to better understand settings and when to use them.
ISO, f-stop and shutter speed settings are inter-related functions allowing a camera to record a picture. Possibly the easiest camera function to understand is shutter speed. When you press the button to take a picture, a shutter is opened to allow light to go on to the sensor array that records your picture. Shutter speed is the amount of time the shutter remains open. On many cameras, shutter speed can be as slow as 30 seconds (or longer) or as fast as 1/4000 second (or faster). Many cameras using auto settings won’t allow you to snap a picture if the shutter speed is less than 1/60th of a second – unless you turn off some of the functions in the menu settings or the auto settings turns on the flash.
We’ve probably all experienced a picture where the shutter was open too long or the light was too bright; the result was a picture that was over-exposed; areas that should have detail were just areas of white on the print. Maybe that brilliant blue sky ended up as a blown-out white area. The exposure time for that part of the picture was too long and over-exposed on the film or sensor array. The opposite common problem is under-exposing where the shutter doesn’t stay open long enough to record the details; end result is a picture that is very dark with little visible detail. [Illustration 004-2]
ISO rating is a direct carry-over from film photography. The ISO ratings, between 60 and 1600 for consumer level film, indicated how sensitive the film was. Generally, more sensitive film (higher ISO) used larger grains of photosensitive chemicals to react to the light more quickly. Less sensitive film (lower ISO) used finer grains of chemicals and took longer to react to light. When the film was developed and photos printed, higher ISO film prints would appear grainier; lower ISO film prints would appear more fine and detailed; this difference would be particularly obvious with larger size prints. The interaction of ISO settings with shutter speed? The higher ISO settings would require a shorter exposure time (or faster shutter speed) for a proper exposure.
F-stop settings translate into the size of aperture inside the lens that light can pass through – basically the lens opening; this rating is also used to describe the speed of the lens. The F-stop of a lens is described with a series of numbers: commonly 2.0 to16. A zoom lens could have a rating of F3.5 – 8; zoomed all the way in (least magnification), the speed of the lens is F3.5; zoomed all the way out, the speed of the lens is F8. The higher the F stop number - the smaller the opening - the less light passes through the lens in a given amount of time - the slower shutter speed needed. The lower the F-stop of the lens, the faster that lens is rated and the more capable that lens will be to take a low light photo without the flash. A lens with a lower F-stop rating is more desirable, but also more expensive because of the optical design problems encountered. [Illustration 004-3]
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Tip #1: Try using the portrait setting. Zoom in and get a good focus on the eyes. Notice in the photo what parts of the pict are in focus. If possible do this in good, natural light so the flash isn’t engaged.
Tip #2: Set the camera for the landscape setting. Take the same picture as in Tip #1 and observe the differences. You should see a little more of the picture in focus (assuming you have sufficient light).
Tip #3: Try the sports setting. First, try a moving object with the camera stationary and not moving. Now try it with the camera panning to match the motion of the moving object (a moving automobile makes a good practice subject for this). Compare the 2 pictures. Any difference in the subject’s appearance? How about the background appearance?
Tip #4: Try a night time setting photo. Set your exposure on some distant lights. Did the flash fire to light a foreground object.
Good quality photos will be partly the result of knowing the capabilities of your camera and how to adjust it for what you need.
Next article: The size of the lens opening sets up another important consideration – depth of field – for next time. In the meantime, try some of the tips and observe the results; we’ll tie those in next time as well. |
