Everyone loves a photo where the subject is in sharp focus and the background is fuzzy or in soft focus. Understanding Depth of Field and how to apply it effectively is what separates the true photographer from the snapshot takers. By the time you finish reading this Factoidz, you will have a good understanding of the fundamentals involved.
Depth of Field’s Three Cornerstones.
Depth of Field is the area in the picture in front of and behind the main subject that is in perfect focus, or, more appropriately put, in relatively perfect focus. Focus is relative because he degree of sharpness will decrease as one approaches the near and far limits of the field. The actual depth of field is dependent on three factors-lens aperture setting, the focal length of the lens, and the actual distance to your subject.
Lens aperture refers to the actual size of the opening through which light passes on its way to the camera’s sensor. The size of the opening is measured in f-stops and the size of the opening is inversely related to the f-stop number. In other words, the larger the f-stop numbers the smaller the actual aperture opening. What we need to keep in mind when speaking of lens aperture in relationship to depth of field is that the depth of field increases as the actual aperture opening decreasing. Depth of Field varies directly with f-stop numbers. The larger the f-stop number, the greater the depth of field.
The focal length of your camera’s lens is a measure of how much the lens magnifies your subject. For example, if your camera is equipped with a zoom lens with a focal length of 28 to 105 mm, the depth of field is inversely related to its focal length. With the lens set at 28 mm setting, its wide angle setting, the depth of field is greatest. Zoom out to 105 mm and the depth of field is at its shallowest. Taking the explanation one step further you will see that with macro photography there is a very shallow depth of field and focusing becomes critical. There’s no room for error when focusing a macro lens.
The distance from the lens to your subject also plays an essential role in the understanding of depth of field. This factor is easy to understand if you simply remember that the further away your subject is the greater the depth of field becomes. With a subject so far in the distance that your camera’s lens is focused on infinity the depth of field also becomes infinite.
Calculating the Depth of Field
The easiest way to master depth of field is through experimentation. Set your camera to aperture priority and then shoot a series of photographs using different lens apertures and focal length settings. The Meta data file attached to your photos will keep track of these settings for you and then you can compare the effects that each setting had on the picture while viewing them on your computer. On the other hand, if you want to be proactive there are many good programs available to help you calculate depth of field. The DOFMaster Depth of Field Calculator is a free Windows based program that you can download and use to print out depth of field charts that you can use in the field. This program is very intuitive and easy to use on any Windows PC. If you would like to experiment with different aperture settings and lens focal lengths to see how they affect depth of field while setting at your desk, here is an online DOF (Depth of Field) Calculator that makes that possible. You can use DOF Master to print DOF Charts for a lens of any focal. Again, this program is very intuitive and easy to master. Another helpful program that is free to download and use is the DOF Hyperfocal Chart program that allow you to print charts out for any given lens.
Better Depth of Field in Four Easy Steps
ï‚· Shutter speed –Vs- Aperture. You probably already know that your camera balances lens aperture and shutter speed to produce the proper exposure for the shot you are making. What this means for you is that you can elect to shoot in Aperture Priority Mode and control the depth of field by selecting the aperture that you want to use. While you control the depth of field by selecting the aperture that will give you that depth of field, your camera will select the proper shutter speed to give you a perfect exposure. What you need to keep in mind as you select an aperture is what shutter speed the camera selects because if the aperture is such that the shutter speed is below 1/60th of a second you will probably end up with noticeable camera shake.
ï‚· Fake it in the digital darkroom using the Layers Tool. Suppose you want a shot where the subject is in sharp focus and the background is out of focus but, for whatever reason, you can accomplish that while shooting the photo. You can always fix that problem in the digital darkroom using a technique called layers. I’ll teach you how to do that using Adobe PhotoShop Elements in another Factoidz.
ï‚· Fake it in the digital darkroom using the Selections Tool. I’ll cover that technique in the Factoidz on how to use the Layers Tool to fake a shallow depth of field like I mentioned above.
ï‚· You can fake an infinite depth of field by using a program called Helicon Focus. This is a handy little program that every serious digital photographer needs to have in his or her digital darkroom toolbox. I’ll cover this program and the basics of how to use it to create the appearance of an infinite depth of field in yet another Factoidz.
