|
The rings are less sharp inside focus as the scope focusing at some point in the atmosphere, rather than at infinity. To get sharp rings at inside focus, the seeing needs to be near perfect, whereas outside focus any night of medium seeing will show well defined rings.
In assessing optics by star test, you are looking for identical distribution of light between the inside/outside focus images. For example, if your outermost ring is dimmer than the rest on one side of focus, an brighter on the other, than you have an issue with the mirrors figure.
|