This study deals with a short but little researched episode in the life of Henry of Isernia, an Italian master of ars dictaminis, who came to the court of King Ottokar II of Bohemia in the early 1270s. Henry’s letter collection contains nine letters relating to his temporary stay at the Premonstratensian monastery in Strahov. These letters are impressive, but hardly interpretable, historical sources, and are also the only ones describing the circumstances of the election of a new Abbot of Strahov that probably took place in 1274. The reliability and credibility of Henry’s sometimes exaggerated and emotionally charged narratives were assessed by comparing their historical and biographical content with existing documents and memorial sources, such as monastery necrologies and annals.
The formulas are derived for calculation of the third-order aberration coefficients for a thick spherical lens in air with a given value of its focal length and for an object at infinity. Equations were described for the re-calculation of aberration coefficients for different values of focal length and also entrance pupil and object positions. and V článku jsou odvozeny vztahy pro výpočet aberačních koeficientů třetího řádu pro tlustou čočku ve vzduchu a pro danou ohniskovou vzdálenost a pro předmět v nekonečnu. Dále jsou uvedeny rovnice pro přepočet aberačních koeficientů pro libovolnou hodnotu ohniskové vzdálenost, polohu vstupní pupily a polohu předmětu.