My estimate for the distance of the farthest Sun-size star that could be focused as a single-whole-star, by a 0.001''-precision telescope, is 30.53 light years. What is your estimate? Same, or different?
This is an approximation to its chord length
# = 2(radius)tan(theta/2)
For the distance of a star approximated to a few significant (sd)
digits only in large distance units like light year or parsec, the
approximation (radius) X theta is OK.
So, the limit asked for is given by
( star distance )
So, star distance d = (star size)/
=(diameter of the Sun)/