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Articles / TULARC / Recreation / Photography / Lenses FAQ / |  |
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10. What are the closest and farthest points that will be inacceptably sharp focus? |
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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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