Discussion is made first on the precision of the Ronchi test when low frequency screen is used and geometrical treatment is permited, then on the precision of the Hartmann test.
The precision of the two tests is briefly shown in a table. For measuring spherical aberration, the Hartmann test is superior to the Ronchi test, and for measuring astigmatism, the Ronchi test is superior to the other.
It is reassured that the Ronchi test has the advantage in that the whole field can be surveyed at once, the separation of aberration is rather easy, and especially the quantitative measurement of astigmatism is conveniently made.
An equation for obtaining astigmatism by using the result of Hartmann test is derived with which astigmatism of an objective lens of a large telescope was calculated finding out that the glass was of good quality.