Depth of Field

Aperture is the only camera control that affects “Depth of Field”, and it is dependent on the lens as well as the focal length of that lens. The science is quite exact, and there are depth of field calculators available on the web. Click here for one of the better calculator examples. ( http://www.cambridgeincolour.com/tutorials/dof-calculator.htm )

Butterfly closeup – by Boomerette
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From an artistic perspective “Depth of Field” is a powerful tool to isolate the subject and place the context in a secondary role by making it more or less “fuzzy”. It mimics human vision, where typically, at least for near objects, only 5% of the observed scene is in focus.

The object of this exercise is to choose a subject and deliberate about the way it shows best against an “out-of-focus” background. Consider the “quality” of the blur as well. Backgrounds can be “real” or artificial.

Henri


May 9, 2017 – Calgary Zoo’s Enmax Conservatory
Depth of Field assignment.

To challenge ourselves we went out to the Calgary Zoo’s Enmax Conservatory. The weather was variable, but predominantly overcast. We prefer lightly overcast, as bright sun creates harsh contrast. Duller, dispersed lighting is better for photography, as you can capture the subtle nuances. The conservatory is a great place to practice “Depth of Field”. There are so many interesting subjects of varying sizes. The large variety of leaf patterns alone can keep you occupied for hours. You can take your time working with your tripod at varying distances, apertures and slow shutter speeds without having to worry about motion blur due to wind conditions.

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This is an example of harsh lighting. For a while the weather cleared and the sun started shining through the conservatory roof and selectively hit this group of flowers, while the background stayed in the shadow. This type of scene grabs the attention right away and human stereoscopic vision gives it wonderful three dimensional depth of field. However a camera with a single lens projecting the image on a flat sensor does not give you this 3D sense. To approximate the human experience of “Depth of Field” you need background “Bokeh”, or out of focus elements in the background. I was quite disappointed when I put this image on the full computer screen.
I was about 50 cm away from the subject and had chosen an aperture of f/4. I had about 5 cm of Depth of Field according to the DoF calculator, just enough to get all the flowers in focus. The harsh lighting caused the background to be too dark for Bokeh. All subtle background aspects were lost as I had to expose for the flowers themselves so not to “wash out” the flower detail.  Although in my mind an appealing picture, it is only suitable for demonstrating the difference between human depth perception and Camera “Depth of Field”.

When taking pictures you might accept what the camera view finder or the LCD screen shows you. You snap and then move on to the next scene. When “Depth of Field” is important to you, use caution, and insure that you take several pictures of the same scene, at incrementally higher f-stops.

Consider a subject at a distance of 70 cm (arms length away). Assume a full frame camera with a 35 mm lens with a maximum aperture opening of f/1.4 and assume you focus exactly in the middle of the subject (at exactly 70 cm distance). Below is the table for depth of field or the acceptably sharp area

Near focus      Far focus      Depth of Field     f stop value
68.34 cm         71.74 cm       3.4 cm                   f/1.4
67.65 cm         72.52 cm       4.9 cm                   f/2
65.45 cm         75.23 cm       9.8 cm                   f/4
61.46 cm         81.30 cm       19.8 cm                 f/8

Depending on how deep the subject is and how rapidly you want the other visual elements in the picture to blur, there is an optimal  f stop value. This is not very apparent in the camera view finder or on the LCD screen. So it is important to take out some insurance. Additional digital images are cheap!

Pink Peace Lily by Boomerette
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This is a good depth-of-field example. The camera focus point is on the tip of the flowering body above the pink leaf and the aperture is just enough to keep all of the pink leaf in focus. The second, still green, flower is somewhat out of focus. The background foliage is several meters away and adds a totally out-of-focus and effective contrasting color background. This picture was significantly cropped. Well done Boomerette!


May 12, 2017  Frank Lake – Zoom Lens Depth of Field

Zoom lenses provide wonderful Depth of Field results, and Frank Lake is a great location  to photograph birds in the reeds. Boomerette created this composition on the inaugural outing with her new 55-200 mm zoom lens (approx. 80 – 300 in 35mm equivalent). Depth of field with a 200 mm zoom focused at about 10 meters at f/4.8 is about 50 cm. The sharpness drops off rapidly, so subjects really stand out from the background. The camera was mounted on a tripod from the boardwalk to the Frank Lake Blind. The position was elevated above the marsh reeds and gives the camera a slight angle down preventing foreground reeds from interfering with the composition. Two straight, vertical background reeds were digitally removed using Photoshop Elements to retain a more consistent curved framing around the bird.