# 10. What are the closest and farthest points that will be inacceptably sharp focus?

## Description

This article is from the
Photographic Lenses FAQ, by David Jacobson with numerous
contributions by others.

# 10. What are the closest and farthest points that will be inacceptably sharp focus?

Sclose = h * So / (h + (So - f))
Sfar = h * So / (h - (So - f))

or, we can define a "hyperfocal ratio", hr = h/(So - f), or roughly the
ratio of the hyperfocal distance to the object distance. Then

Sclose = So * hr/(hr+1)
Sfar = So * hr/(hr-1)

These formulas are also correct when hr is defined as hr = h/So and
the N used in computing h is actually Ne.

If the denominator is zero or negative, Sfar is infinity.

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