Bellows Extension at Hyperfocal.

[Reciprocity_Failure]

Hello,

I know that if bellows are extended to focal length of the lens, the lens is focused at infinity. If belllows are extended to double focal length, the subject is 1:1.

However is there a way to CALCULATE the bellows extension to focus at hyperfocal distance (or any predetermined distance) ?

Regards

RF.

[Leigh]

Fine point...

When focused at infinity the lensboard will be forward of the film by a distance equal to the Flange Focal Length (FFL) of the lens, which is usually not the same as the optical focal length. For short lenses the FFL is usually longer than the focal length, while for long lenses it is usually less, sometimes by a large amount.

When focused for 1:1, the lens will move forward from its infinity focus by a distance equal to its actual focal length, which may differ slightly from the marked value.

The standard formula for optical separation is:
1/F = 1/Di + 1/Ds where F is the focal length, Di is the image distance, and Ds is the subject distance.

This formula disregards the difference between FFL and optical focal length, but the error is small enough to be disregarded except for long lenses.

- Leigh

[Emmanuel BIGLER]

We can add that when the camera is focused to the hyperfocal distance H = f^2/(Nc), where "N" is the f/number and "c" the diameter of the circle of least confusion (chosen by the photographer to meet his specific requirements, and not at all proper to the lens !!) the additional bellows extension beyond the focal point is simply : Nc.
Does not depend on the focal length !!
For example; if your f/number is 22 and your circle of confusion 150 microns, the additional bellows extension @H is 22x0.150 mm = 3.3 mm.
And the additional bellows draw beyond the focal point required to reach the 1:1 ratio is one focal length, even of the lens is a telephoto, for which the flange focal distance is much shorter than the focal length.

[John Koehrer]

Or use this:http://www.dofmaster.com/charts.html