After a well deserved holiday break, here were are at Lesson 3 of Food Photo 101!
I peeked at Nika’s photos for this and had a good idea that we were going to do one of the topics I’ve really been looking forward to doing, Depth of Field. Here’s the lesson, in Nika’s words…
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.
- 1) The background is 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.
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.
- 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.
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 can’t wait to see what you all get this time around.
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