You currently own one of the finest enlarging lenses made. Diffraction is caused by light thatís distorted by grazing the edge of the aperture blades. Thatís the same in all lenses. Diffraction isnít caused by the glass. The 50/2.8 EL Nikkor has the best combination of resolution and preservation of contrast closed 2 stops at f/5.6. It also works well at f/4 to at least f/8. The further you close the aperture, the higher the percentage of diffracted image-forming light. This is true of all lenses.
If your prints are truly soft, then you have to start looking for the actual cause. The Omega B22 is as good or as bad as your abilities to set it up properly. Iíve seen exceptional prints made on simple enlargers like the Omega B22 and some truly hideous ones made on very expensive Durst enlargers. Print quality is due to the skill of the user and his or her ability to analyze problems and correct them.
The biggest problem is keeping the negative flat during the exposure. The root cause of unsharpness in enlarging is often the warming of the negative as it absorbs heat from the light passing through it. That makes it belly up and out of the shallow depth of field during the exposure.
We combat this with a heat-absorbing glass filter well above the negative, a glass sandwich negative carrier, or both. If your B-22 isnít equipped with either the 473-101 or the 473-113 heat-absorbing glass filters (assuming that itís equipped with the common condenser lamphouse), then keeping the negative cool and flat in a standard carrier is impossible.
If you make a 8.5Ē-wide projection of a 35mm negative with a 50mm lens at f/5.6, the DOF about the plane of focus for the negative is about 0.35mm or 0.014Ē. If the negative moves more than half of that distance in warming, the projection will begin to degrade.