Pentax 6x7 Manual page 27

Diaphragms are not employed with the reflex
lens design. Light adjustments with the 1000
mm Takumar are made by employing a system
of four ND (Neutral Density) filters which are
built into the lens and serve as substitutes for
lens aperture settings. These do not, however,
increase the depth of field as does stopping
down a lens. The depth of field for the stan-
dard fiB aperture of this lens remains in effect,
regardless of the filter used .
An N D filter ring is located on the rear section
of the lens barrel as shown in the photos
below. To change filters, rotate the ring until
the desired filter aligns with the white index
mark. Be sure the filter click-stops in place or
it will not align properly.
The 1000mm Reflex Takumar also has three
regular filters built in (Skylight, Y2 and R2).
The control ring for these is located adjacent
to the N D filter ring. at the rear of tHe lens.
Rotate the ring the same as the ND ring until
the engraving indicating the desired filter
aligns with the index. There is also a blank
setting in addition to the three filter settings
which features a neutral colorless glass lens.
Numerals beside the filter designations on the
filter rings indicate filter factors. (Refer to page
11 for instructions on the use of other filters) .