Schneider Optics PC-SUPER-ANGULON 28 mm f/2.8 - Manual (Page 12)

¡2 Focusing and Depth of Field
The focusing of wide-angle lenses appears to be relatively non-critical due
to their large depth of field . However, careful focusing is actually necessary
to utilize the high imaging quality of this lens to the full . To ensure maxi-
mum brightness of the focusing screen and the best recognition of the ide-
al focusing point, the aperture should be opened by pivoting the stopping-
down lever toward the shifting knob . The aperture setting ring therefore
remains on the set working aperture so that the aperture can later again
be closed to the working aperture quickly using the stopping-down lever
directly before the shot without moving the eye from the viewfinder .
Focusing can generally take place before or after the parallel shift as de-
sired . However, if the LED focus display of an autofocus camera is used for
manually focusing, focusing must take place in the centered position (i . e .
with a non-shifted lens) because the AF sensor requires incidence of light
approximately parallel to the axis, but the light is obliquely incident on the
sensor when the lens is shifted . The parallel shift which then takes place
after the focusing does not influence the set distance .
The f-numbers at both sides of the index mark for distance and aperture
indicate the depth of field: If e . g . everything from ¡ m to 3 m should be
sharp, the distance ring should be set so that the meter figures ¡ and 3 are
above the same f-number (here: 8) at both sides of the index mark .