Angela Nicholson looks at the Canon EOS 7D and EOS 5D Mark II to see whether full frame still holds an advantage over APS-C-format cameras
Canon 5D vs 7D – Depth of field comparison
Image: This table compares the depth of field at the same effective focal length with APS-C and 135 format
When an APS-C-format camera is used to record the same composition as a full-frame model, the images from the smaller-format camera have greater depth of field at any given aperture. The properties of the lens and aperture in use don’t magically change, but getting the same composition with an APS-C-format camera means that it must either be moved further away from the subject than the full-frame model, or a shorter focal length optic must be used. Both of these factors result in greater depth of field.
The table below compares the calculated depth of field at f/8 with an APS-C-format camera such as the EOS 7D with a 50mm lens mounted and the full-frame EOS 5D Mark II with an 80mm lens at a range of subject distances. These two different focal lengths produce the same framing on their respective format cameras.
In every instance the zone of acceptable sharpness starts closer to the camera and extends further beyond the subject with the APS-C-format camera than it does with the full-frame model. This can be extremely useful for landscape and macro photographers who want extensive depth of field or perhaps even front-to-back sharpness in their images. However, when shallow depth of field is needed to isolate the subject, a wider aperture is required with the EOS 7D than with the EOS 5D Mark II.
When shooting a subject with near 1:1 magnification with both the EOS 7D and EOS 5D Mark II using a Sigma 105mm f/2.8 EX DG macro lens, for example, I found that the aperture needed to be closed down to f/4 with the EOS 5D Mark II to produce a similar depth of field to
the EOS 7D at f/2.8.
Image: The extra magnification of the APS-C-format sensor gives this macro image more impact