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1. Originally Posted by Ian C
Here are a few depth of field comparisons at a subject distance of 10 meters (lens to subject) and f/8.

The numbers are: format, magnification, circle of confusion, focal length, and DOF.

The lenses are approximately the “normal” focal length for each format.

35mm, 0.005X, 0.029mm, 50mm, 125.3m

4 x 4cm, 0.006X, 0.038mm, 60mm, 56.8m (obsolete 127 format)

6 x 4.5cm, 0.008X, 0.047mm, 80mm, 17.7m

6 x 7cm, 0.009X, 0.059mm, 90mm, 17.3m

4” x 5”, 0.0152X, 0.110mm, 150mm, 9.0m

8” x 10”, 0.031X, 0.220mm, 300mm, 3.9m
I like the table computed at 100m with a constant linear aperture of 6.25mm

2. Using a constant 6.25mm aperture, for each lens cited and the resulting aperture value, the hyperfocal distance is less than 100m. Therefore, we get infinite depth of field at 100m in each case.

Here it’s useful to find the near limit of the DOF, as that’s something we can use.

Here are: format, focal length, aperture, and near limit of DOF at 100 meters with a constant 6.25mm aperture.

35mm, 50mm, f/8, 9.7m

4 x 4cm, 60mm, f/9.6, 9.0m (obsolete 127 format)

6 x 4.5cm, 80mm, f/12.8, 9.6m

6 x 7cm, 90mm, f/14.4, 8.7m

4” x 5”, 150mm, f/24, 7.9m

8” x 10”, 300mm, f/48, 7.9m

As can be seen in the table, the near limit of DOF is nearly constant over the range formats for a constant aperture of 6.25mm and a lens-to-subject distance focused at 100m.

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