Assertion: lens's element | /r/HasProperty | positive
Facets:
Source sentences:
text: Since ϕ 2 = − ϕ 1 V 2 / V 1 {\displaystyle \phi _{2}=-\phi _{1}V_{2}/V_{1}} , and the Abbe numbers are positive-valued, the power of the second element in the doublet is negative when the first element is positive.