Older, wide aperture lenses sometimes have an optical problem called focus shift, due to spherical aberration, where the focus point shifts a bit between when the lens is opened up all of the way and when it is stopped down a bit. If your lens has enough optical aberrations when opened up to make such precise focus impossible, then precise focus also doesn't matter, as the image will be rather fuzzy anyway. I assume you are trying to focus with the lens opened up all of the way? If that is the case, and if you are going to stop the lens down for capture, then excessively precise focus won't matter.

Instead, any high-contrast object should do to help you focus. The Bahtinov mask is used to focus telescopes on stars.

The Siemens Star and the 1956 chart were used in the past to determine camera system resolution and are not focus aids, they have since been pretty much obsoleted and other kinds of charts are now used to determining resolution. I thought about using something similar to a bahtinov mask or this chart ( ) however about the former most of my subjects aren't point light sources (and also focal lengths are too short). I've tried a Siemens star ( ) however after reaching a certain degree of focus precision, I can still slightly rotate the focus ring left and right without being able to tell a difference or which ring position yields a better focus.

Siemens star focus chart