ARTICLE 12–LENSES CONTINUED—DEPTH OF FIELD
ARTICLE 12—-LENSES—DEPTH OF FIELD
Furthering our discussion of lenses and the characteristics of them, the topic of “depth of field” enters the arena for an in depth review. When we discuss the feature of depth of field, the reader should be informed that the greatest
amount of depth of field is commonly generated with wide angle lenses. Depth of field or depth of focus as some refer to it can be described as follows: the amount of space or distance “before or after your point of focus that is in acceptable
sharpness”. Many people have difficultly grasping this technique, so I will address it systematically enabling a photographer to comprehend and implement this formula to their best advantage. As mentioned, wide angle lenses have the greatest
amount of depth to them however, the reader should realize that all lenses contain depth of field capabilities. Medium to longer length telephotos and long range zooms are limited in their depth of field range. A simple reference regarding lenses in a general sense would be that the longer the lens you mount on your camera, the less depth of field you will have.
How To Understand And Implement Your Lens Settings Correctly:
For the purpose of this example, I will refer to the above mentioned, 28mm wide angle lens. For this example, I will set the lens at a focus distance of 10ft. Now, the reader has to make a decision as to what working aperture (F stop) you
wish to set your lens at. I’ve chosen to select F8 on my aperture ring. For alternate camera designs that do not have adjustable aperture rings on the lens, you can adjust the cameras aperture on your LCD screen. Looking at your lens, if applicable, you will notice a set of numbers representing your distance scale,( the point at which your lens is actually focused at-10ft), and another set of numbers, being the aperture scale representing the various f-stops on your lens. F stop numbers are typically displayed as F2.8, 4, 5.6, 8, 11, 16, 22 etc. You will also notice particularly on the somewhat older style lenses, another scale of numbers in between the focus scale, and the aperture row. This third row of numbers is your depth of field scale. I must point out at this time that in my opinion the newer, more current lenses on the marketplace do not always contain a depth of field scale. It is astounding that lens manufacturers have elected to omit this important scale from certain current lens designs, and in my opinion it is a serious error of lens development. If you have one of the more current lenses and it dose not contain a depth of field scale, consult your owners manual. Often, manufacturers have printed a small page of depth of field tables for people to refer to, if the actual lens itself does not display them. To continue, what you want to do at this point is to determine how much depth of field your 28mm lens has when set at F8 at 10ft. You will notice on your lens, a focusing indicator or line, frequently painted in orange, red or yellow. This tells you exactly what point you are focused at. (Our example of 10ft. should be set at this coloured line). Referring to the depth of field scale on the lens, you will now search for the F8 aperture marking on both sides of the coloured focus indicator line on the depth of field scale. My 28mm lens contains two F8 markings on the depth of field scale-one on either side of the coloured focus indicator line.
Now, to determine exactly how much depth of field you have “before” 10ft. you look for the F8 aperture- (F stop) mark on the depth of field scale to the “left” of your point of focus. Once found, follow that number straight upwards to the distance scale-(people often draw imaginary lines upwards from this depth of field scale to the focus distance scale). On my lens, the number 5ft. is directly above the F8 marking on the depth of field scale. This means that the amount of acceptable sharpness, or depth of field before your point of focus is 5ft.-(5 ft. of additional sharpness or clarity before 10ft.) Now, repeat the procedure on the opposite side of the point of focus line, and once again make reference to the depth of field scale; the right side. To obtain how much depth of field you have “after” your 10ft. point of focus, look for the F8 marking to
the “right” of the focus indicator. Once found, follow it straight upwards to see what distance number it is registered at. My lens now indicates the distance of infinity. This means that if I set my lens to F8 while making photographs, and my
focus to 10ft., I will have an additional “area” of acceptable sharpness from 5ft. before my point of focus, to infinity after the actual point of focus that I can depend on with levels of accuracy when viewing my finished imagery. This technique of predicting depth of field has tremendously benefited photographers over the years and it’s graces are numerous. At this time, it would be beneficial to the reader to fabricate an example listed below, and put this theory into a practical excersize.
You wish to create pictures of the Prime Minister as he/she is exiting the Parliament buildings. Rows of photographers are directly in front of you blocking your view leaving you no time to actually focus your lens on your subject. Finally, an opportunity presents itself when your subject is visible and within approximately 15 feet from where you are standing. As well, you are able to produce only one image of the subject before he/she enters the awaiting vehicle. If you had your lens configured similar to the example I just provided, you would have ended up with a photograph that was certainly acceptable and worth printing. You already determined that if you set your 28mm lens to F8, your depth of field would extend to infinity, and that is the key point right here. Failing is practically non existent following this technique. Your lens is informing you “even before you make the image” that it is going to produce a picture ensuring levels of sharpness extending from 5ft. to infinity. On a further note: the wider the lens is, and the “smaller the f-stop” used, the greater the depth of field becomes. This technique will benefit you time and time again if you don’t have the opportunity to focus on your subject matter. Even if the new generation of lenses do not display depth of field scales, your level of knowledge has now increased immeasurably by investing the time to learn this information and apply it to your picture making habits. It should also be mentioned that the term “hyper focal focusing” relates specifically to depth of field. It is a technique that photographer’s utilize when making reference to their depth of field scales, determining exactly what area or zone of sharpness the lens will deliver at any given aperture. For instance, if a person wants the maximum amount of depth of field from a 28mm lens, the lens will be set at a small lens opening such as F16 or F22. If a person desires only a small depth of field range, then setting the lens to F2.8 or F4.0 will fulfill the photographers needs quite nicely.
Create a few practice images on the end of a roll of film or some specific area on your memory card next time you wish to test this technique. Have a person stand approximately 10ft. away from you and produce a full length image of them at F8-(our previous example f-stop). Have perhaps another person stand far behind them, or use the background of your house as an example. Then, while standing in the same position, produce another image at F2.8, then another at F22. Each time you change your f-stop, the background of your photographs will change. As mentioned, because wide angle lenses have so much inherent depth of field initially, the effect will not appear to be as great as compared to medium telephotos or longer range zooms. Produce a series of tests with other lenses in addition to wide angle lenses. If you own a standard lens or medium range zoom, repeat the above scenario. Always pay strict attention to the clarity before your subject and after it as well when creating this imagery. The smaller f-stops-(F16, 22, 32 etc.) will make a background appear much sharper and clearer than if your lens is set at the wider F stops (F2.0, 2.8, 4, etc.) Run a series of tests utilizing all apertures on your lens. A simple way of proceeding would be following the example above, and have a friend stand approximately 7-10 in front of your camera; then adjust your light meter accordingly so that you can produce imagery utilizing “all the f-stops” that your lens has to offer.
I have accessed the technique of depth of field control for over 40 years when producing imagery. This feature becomes very dependable and in particular, photographing people in movement. A further example would be when I am contracted to photograph a wedding. When people are walking up and down the aisle of a church for instance, I seldom have the time to look through the camera to make fine focus adjustments due to the rapid movement of the participants. Depth of field or zone focussing has delivered excellent results with very acceptable levels of sharpness that your viewer would find more than satisfactory.
You will find that more you become familiar with this technique, the more diversified your picture making will become. You will start becoming more selective as to how important you wish the background of your imagery to be. This is an excellent feature on all lenses and provides the user the pleasure of creating their “own style” of imagery meaning….perhaps a photographer prefers razor sharp backgrounds as a characteristic of their imagery as opposed to an out of focus background appearance.
As with any new lens or alternate piece of photographic equipment you purchase, one develops a sense of familiarity with the product or technique with time invested in this area. Learning to “see” photographically is greatly enhanced with depth of field knowledge. If you have a camera that offers a depth of field preview button, this is unquestionably an excellent feature to become affiliated with. This feature will visually let you preview the scene with your selected F stop prior to actually making the photograph. The reader should be made aware that when selecting F stops on their aperture ring of approximately F8 or smaller while depressing the depth of field preview button, the area you are viewing will appear to become darker. This is common and an indication that your camera is operating properly. When using smaller F stops such as F 22,32,45…the viewing area will become so dark that you may not be able to see through your viewfinder at all. Again, this is commonplace. What is taking place at this time is that while the aperture is becoming smaller in your lens, it is preventing a large quantity of light to enter your viewing system therefore making the entire viewing area dark. By “SLOWLY” depressing your depth of field preview lever in and out, you will notice that the scene becomes gradually darker to lighter. During this movement, you will be able to judge the clarity of the background and foreground even when the image itself is becoming darker. The more you experiment with your various F stops, the more your eye will become accustomed to seeing in these varying light conditions taking place in your viewfinder.
Preconceived perception of visual design is absolutely mandatory if a photographer is to take their work seriously and elevate their status to a higher level of professionalism.
With Good Wishes,
Ottawa/Kanata Photographer, Jeff Ryan/Ryan Studio, Ont.
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