Depth of Field Card

Despite some research, I never found a depth-of-field card matching my personal requirements, so I had to design one... I was looking for a quick to use table, just giving me an order of magnitude. In the field, I always end up adjusting the aperture with the depth of field test button, or rarely the EOS  20D A-DEP mode (I miss the EOS 33 / Elan 7 DEP mode). My use of Canon's DEP AE modes is well detailed in Michael Reichman's tutorial (DEP on The Luminous Landscape).

I will not give you a lecture on the depth of field subject, as it is fairly well explained on Wikipedia. The acceptable cercle of confusion is often defined as the sensor's diagonal divided by 1440. This gives 0.030 mm for 24x36 mm film (or a full frame sensor) and 0.018 mm for the 15x22.5 mm sensor of the EOS 20D. For an average eye with 2 arc minutes of angular resolution (cf. "Encyclopædia Universalis" for excellent contrast and illumination conditions), this means looking at an X x Y enlargement (Y = 1.5 x X) from a distance of 2 x L (40 cm (16") for a 20x30 cm (8x11") enlargement).

Take notice that for the EOS 20D, the conventional cercle of confusion represents 2.8 pixels! This size is about the best you can get with any Bayer type sensor, as you need at least 2 pixels to capture the finest detail, and multiply by a square root of 2 coefficient for Bayer demosaicing. Indeed, I consider (very optimistically) that perceived resolution correlates with the number of green pixels which bear most of the luminance information: a sensor of 8.2 million Bayer pixels would be equivalent to a Foveon type sensor of about half as many "real" pixels (4.1 million).

Here is the instance I use with a 0.018 mm circle of confusion:

• Each table refers to a focal length, except the last one reserved for large focal lengths at f/8.
• Rows: apertures (for the first tables).
• Columns: focus distance in meters as set on the lens.
• Last column : hyperfocal distance in meters for the considered aperture. If the lens is set with the hyperfocal distance, the image will be considered "in focus" from half the hyperfocal distance up to infinity.
• In black: actual depth of field in meters.
• In red (negative values): the lens is set past the hyperfocal distance. The image is considered "in focus" from this value below the distance set on the lens up to infinity.