FP101-3: Depth of Field

November 27, 2007 in Food Photo 101, photography

Depth of Field

This week’s topic will be Depth of Field (DOF) . Remember that I am putting together a food photo glossary for those terms that may not be as commonly known. I will also try to link as many of them in the text to the wikipedia entries.

What is this Depth of Field I speak of?

The depth of field is the distance in front of and beyond the subject that appears to be in focus. (*)

The wikipedia has a very extensive discussion of DOF and I would recommend your slogging through the non-math parts, maybe twice.

I like to visualize the DOF as a slice of paper (representing the focal plane) that floats in front of my camera. It can have different thicknesses and positions in my photo depending on the setting in the camera, the setting in the lens, the tilt of the camera, and the position of the camera relative to the subject.

If one has a shallow DOF, that piece of paper or focal plane (or plane of focus, POF) floating in front of my camera is very thin and will capture only a small slice of the subject in sharp focus.

If the DOF is deep then the focal plane is very wide (the piece of paper gets thicker) and thus a much thicker slice of the subject will be in sharp focus.

One of the settings on your camera that has a direct impact on DOF is the aperture or f-number.

For a given subject framing, the DOF is controlled by the lens f-number. Increasing the f-number (reducing the aperture diameter) increases the DOF; however, it also reduces the amount of light transmitted, and increases diffraction, placing a practical limit on the extent to which the aperture size may be reduced. … Aperture settings are adjusted more frequently in still photography, where variations in depth of field are used to produce a variety of special effects. (*)

There are ways of modifying the usual formula of DOF for one’s camera. Special types of lenses called tilt-shift lenses modify the angle of incidence of the photons traveling through the lens and impacting the sensor. Instead of hitting the sensor on a 100% perpendicular (90 degree angle), the light hits the sensor at an angle.

The wiki says:

When tilt is applied, the film or image sensor is not at a right angle to the optical axis of the lens, causing a gradient of focus. (*).

This technique can give some interesting effects in food photography and also in other photography that yields a “toy” like sense to an otherwise normal landscape (called miniature faking). In this case, by modifying the DOF and the gradient of focus drop off, one can make a scene seem like it is very close in and being shot with a small f-number (as you would for macro shooting).

Here are a few links to examples of that.

Tilt-shift lenses are obviously for SLR lenses and they can be expensive.

For example, the Canon Normal Tilt Shift TS-E 45mm f/2.8 Manual Focus Lens for EOS – A mere $1,069.95

Digging into DOF

To try to give you an intuitive sense for DOF, I am going to share a few shots with diagrams that point out how the shot was done, with the focal plane indicated. The photos will also be marked up to help with the discussion.

Set-up 1

FP101-3: DOF

Here we have a shot of a chicken quenelle skewered with a rosemary sprig, surrounded by a couple of coconut oil fried white pepper encrusted chicken pieces. The quenelle is covered with a turmeric hollandaise sauce.

The EXIF data indicates: ISO500, exposure 1/125 at f/3.5. I shot it with my Canon 30D and the 50mm 1.4 USM macro lens. I used a daylight balanced strobe on the left and a styrofoam block on the right.

FP101-3: DOF

The composite image above points out several regions with differing focal qualities.

  • 1) The background and out of the focal plane
  • 2) Region of interest on the quenelle, highlighting the crushed white pepper bits – sharp focus
  • 3) Region of interest on the forward chicken piece that doesnt have optimal focus like I would want but its the best we got.

FP101-3: DOF (1)

The diagram above is approximately the positioning of the subject and the camera. I have used light purple bars to indicate the focal plane.

Set-up 2

This next set-up shows some Christmas cookies on a cake pedestal. This series shows you how different a shot can feel when the focal plane shifts.

FP101-3: DOF (3)

Here is a general shot of the set up seen above.

FP101-3: DOF

In the images below, the white and black lines indicate the focal plane.

FP101-3: DOF

The EXIF data indicates: ISO100, exposure 1/80 at f/2.5. I shot it with my Canon 30D and the 50mm 1.8 USM macro lens. I used ambient daylight coming in through the window to my right.

FP101-3: DOF

The EXIF data indicates: ISO100, exposure 1/100 at f/2.5. I shot it with my Canon 30D and the 50mm 1.8 USM macro lens. I used ambient daylight coming in through the window to my right.

You can decide for yourself which image might be best. You might think that it would have been better to make the focal plane horizontal with the cookies so that all of them would be in focus.

Set-up 3

FP101-3: DOF (2)

If one shoots almost straight down, the DOF will take a horizontal slice out of your subject.

FP101-3: DOF

Here we can see how the leaves are caught in focus but the background is slightly out of focus. Because I had the camera slightly tilted, the tabletop is more focused near the subject and less so off to the upper right.

  • 1) Leaves are in sharp focus
  • 2) Even the lower cilantro leaves are in focus. This indicates a medium DOF.
  • 3) The tabletop near the leaves is slightly out of focus so we can still get some detail
  • 4) The upper right corner is more blurry, giving some softness to the image.

Your Task

Shoot a food subject, using a tripod, while you vary the aperture on your camera. If you have a “macro” mode, use it. If you have a DSLR, be on full manual mode. P&S, you go as manual as you can get and try all of the settings of your aperture function.

Post back to the Flickr Food Photo 101 pool. If you are familiar with photoshop or some other graphics program, make up a diagram of your shot with the focal plane indicated.

Most of all, have fun!

I cant wait to see what you all get this time around.

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