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.

    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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