The discs add more SF effect. The aperture on the disc is the "effective" aperture with it in place. you can shoot whatever aperture you want, with or without discs. Stopping down more (f/8 or more) reduces or eliminates the SF effect.
Are you sure? The discs close the aperture down and in my experience sharpen the image when the primary aperture is wide open.
The Mamiya sheet can be found and I'm sorry but my slow connection (and maybe APUG) doesn't allow me to upload it, but here's the "skinny" (I'll learn to speak American yet):
Focusing
The special spherical aberration used in this lens to produce the soft focus effect
causes some discrepancy in focusing when this is done at full aperture; therefore,
when focusing always stop this lens down to at least f/8 to cancel the soft focus
effect.
The No. 1 Matte and No. 2 Checker focusing screens are ideal for use with this lens.
The No. 3 Rangefinder Spot or No. 4 Microprism focusing screen may be used,
however, by stopping down to f/8 or more and using the mat area.
1. Set the lens aperture at f/8.
2. Press the depth-of-field preview lever down. The lever locks into position
automatically.
3. Focus.
4. Set the lens to the desired aperture.
5. Return the depth-of-field preview lever to its original position by slightly
pressing it in the return direction. The lever will then return automatically.
Adjustment of the Soft Focus Effect
The degree of soft focus effect varies depending on whether or not the Softness
Control Discs are used and in accordance with which of the three Discs is used. The
amount of effective softness, however, will also depend on the type of subject,
distance, lighting conditions, the amount of enlargement given the negative, the
concept, personal Iikes, etc.
1. When not using a Softness Control Disc
The soft focus effect varies depending on the aperture used. At full aperture (f/4)
the softest effect is obtained. The effect is less at f/5.6 and completely disappears at
f/8 or smaller apertures to produce a normal sharp image.
2. When using a Softness Control Disc
There are three different types of Softness Control Discs, each with a different
diameter hole in the center.
* Always set this lens at full aperture (f/4) when using one of the Softness Control
Discs. The f-value of this lens changes according to the Disc used. When the No. 1
Disc is used the effective lens aperture is approximately f/5; for the No. 2 Disc this
value is approximately f/5.6; and for the No. 3 Disc it is approximately f/6.3.
How to attach the Softness Control Discs
1. Remove the front lens barrel by rotating it counterclockwise.
2. Slip the disc to be used over the rear end of the front lens barrel.
3. Put the front lens barrel back into place and tighten by rotating it clockwise.
Depth-of-field
The depth-of-field and the degree of softness can be easily checked by stopping
lens down to the preset aperture by operating the depth-of-field preview lever.
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