Short answer.
With traditional polishing the curves are pretty good and consistent.
The figure 3 Newton rings.
Astigmatism may be a problem.
In bulk polishing the lenses at the edge are less good than in the centre.
Modern high speed polishing is considerably less accurate and modern standards have slipped.
The exotic glass is more likely in the eyepieces for the original question.
Who the maker is determines quality.
As to getting curves from x-ray images my personal opinion is that it is a non starter.
Regards,
B.
With traditional polishing the curves are pretty good and consistent.
The figure 3 Newton rings.
Astigmatism may be a problem.
In bulk polishing the lenses at the edge are less good than in the centre.
Modern high speed polishing is considerably less accurate and modern standards have slipped.
The exotic glass is more likely in the eyepieces for the original question.
Who the maker is determines quality.
As to getting curves from x-ray images my personal opinion is that it is a non starter.
Regards,
B.