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  • Understanding depth of field

    This is the first short tutorial in a series of posts aimed at helping you to understand your camera better, getting more control over your photos and getting off the auto mode.
    I will try to make these as simple as possible, should you wish to try to do some of these techniques every tutorial finishes with exercises you can do at home with minimal equipment.
    You will need a minimum of either a professional or high-end compact, a mirrorless or DSLR camera.

    Dictionary.com describes depth of field as follows:

    the range of distances along the axis of an optical instrument, usually a camera lens, through which an object will produce a relatively distinct image

    In simpler terms, depth of field describes the distance of what is in focus in a single photo and is also a creative technique to bring attention to a subject or subjects in a photo.

    There are three main factors that affect depth of field, these are namely Aperture, Focal Distance and the Lens, I will be discussing all 3 in this post.

    Aperture

    The lower the f-stop or the wider the aperture, the shorter the depth of field becomes or the less in focus as demonstrated in photographs below
    f/2.8f/4f/5.6f/8f/11f/16f/22f/32

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    f/4 Sample

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    f/5.6

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    f/8 Sample

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    f/11 Sample

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    f/16 Sample

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    f/22

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    f/32 Sample

    Canon EOS 70D with Canon EF 100mm f/2.8 Macro lens
    You can see how the photographer figurine stands out at f/2.8 and blends in to the crowd at f/32.
    The focus point, focus distance, and lenses have not changed for any of the photos above, all the changes are in camera using the aperture setting.
    There is far more to controlling depth of field then aperture, these factors are just as important to remember when trying to shoot creatively.

    Distance

    The second of these factors is the distance between the camera and the subject, also known as focal distance, this can and often does affect the depth of field.
    The closer you are to the subject the shorter the depth of field, inversely the further you are from the subject the wider the depth of field as demonstrated below.

    60cm2m
    f/2.8 from 60cm
    f/2.8 from 2m
    Both photos were shot at f/2.8, notice how the one shot from 2m away has more depth of field then the one shot at 60cm? In fact, it is now closer to the f/8 at 60cm where we can start to see the mad scientist eyes.
    Have you noticed that a shallow (or short) depth of field can be achieved at f/5.6? Most kit lenses are in the 18 to 50mm and f/3.5 to 5.6 ranges, making it possible to get photographs like these with an inexpensive kit.

    Lens

    The third but not last, the lens length and the number of diaphragm blades affect the look of the “blurred” part of the photograph.

    Lens length
    As the lens length increases so does the the compression effect, which will be discussed in a later post, but more importantly both the focus distance and thus the depth of field shrinks, I will not go into the science of it, just know that it is true.

    Short lensLong Lens
    Canon EOS 700D with EF-S18-55mm f/3.5-5.6 IS STM, f/3.5, 1/30 sec, ISO 100, 20mm

    Canon EOS 700D with EF-S18-55mm f/3.5-5.6 IS STM, f/3.5, 1/30 sec, ISO 100 (at 20mm)
    The camera is laying on the sweet bags.

    Lion

    Canon EOS 5D Mark III with Canon EF 500mm f/4 L II USM, f/4, 1/500s, ISO 1600 (at 500mm)
    The camera was more then 25m away from the lioness notice how the back ear is already out of focus.

    Bokeh
    Bokeh is the patterns created by the diaphragm blades and higher the aperture, or the lower the f-stop, the more pronounced the Bokeh in the blurred sections of the photograph as shown below.

    SONY Alpha 6000 with SONY E 30mm f/3.5 OSS Macro, f/3.5, 1/250 sec, ISO 100 (at 30 mm)

    SONY Alpha 6000 with SONY E 30mm f/3.5 OSS Macro, f/3.5, 1/250 sec, ISO 100 (at 30 mm)

    Bokeh may look a lot like lens flare, it is not as it is usualy done on purpose but it can happen accidentally and is something to watch out for. Bokeh is a subject on it’s own and will be discussed in a later post.

    Practice Exercise

    Take 3 to 5 glasses, champagne glasses, add sparkling water for more interesting photos, put then in a line and separate them by about 10cm on a flat surface like your dinning table.
    If you have a support for your camera like a tripod, mount and frame the glasses at a slight horizontal angle from the straight line you created with the glasses so you can see all the glasses, if not just frame manually as explained. You ideally need to have something to support your camera, a sturdy box will do.
    Tip: If you are using water, make sure it is room temperature, if it is cold the glass may condense and mist up.
    Set your camera to Aperture Mode (Av on Canon, A on Nikon) set it to the lowest f number available, for most 18-55mm kit lens would be between 3.5 and 5.6 depending on your zoom setting.
    In the aperture mode all other settings will be automatic, I shoot 80% of the time in aperture Mode.
    I recommend the longest zoom setting, for example 55mm and f/5.6 and getting as close as possible.
    You should get something like this:

    Canon EOS 70D with Canon EF-S 18-55mm f/3.5-5.6 kit lens, f/5.6, 1/15 sec, ISO 100

    Canon EOS 70D with Canon EF-S 18-55mm f/3.5-5.6 kit lens, f/5.6, 1/15 sec, ISO 100

    From here, raise the aperture (f number) to 8,11,16,22,etc and see the results, then go back to 5.6 (or lower if available) and move towards your subject and away from your subject shoot each scenario.
    Tip: You may find it easier to focus manually using the live view function of your camera.
    Last tip: Read the manual to find the functions mentioned in this exercise, if you still battle leave me a note.

    Lastly, the sensor size also affects the depth of field, this is one of the reasons professional photographers favor full frame sensors (36x24mm or 35mm film equivalent) or even medium to large format cameras as these give a shorter depth of field.
    I will discuss the differences in sensor sizes and the importance in a later post.
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    Tuesday, 5 April 2016 • Tutorials • Views: 434

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