Editing Scheimpflug principle (section)

===Selective focus===
[[File:Jcouples17.jpg|thumb|James McArdle (1991) ''Accomplices'']]

The region of sharpness can also be made very small by using large tilt and a small ''f''-number. For example, with 8° tilt on a 90&nbsp;mm lens for a small-format camera, the total vertical DoF at the [[hyperfocal distance]] is approximately{{Efn|The example here uses Merklinger's approximation. For small values of tilt, {{nowrap|sin&thinsp;''θ'' ≈ tan&thinsp;''θ''}}, so the error is minimal; for large values of tilt, the denominator should be {{nowrap|tan&thinsp;''θ''}}.}}

: <math>2J = 2 \frac {f} {\sin \theta} = 2 \times \frac {90 \text{ mm}} {\sin 8^\circ} = 1293 \text { mm} \,.</math>

At an aperture of ''f''/2.8, with a circle of confusion of 0.03&nbsp;mm, this occurs at a distance ''u′'' of approximately

: <math>\frac {f^2} {Nc} = \frac {90^2} {2.8 \times 0.03} = 96.4 \text { m} \,.</math>

Of course, the tilt also affects the position of the PoF, so if the tilt is chosen to minimize the region of sharpness, the PoF cannot be set to pass through more than one arbitrarily chosen point. If the PoF is to pass through more than one arbitrary point, the tilt and focus are fixed, and the lens ''f''-number is the only available control for adjusting sharpness.