Final answer:
The power of a rigid contact lens for a farsighted person with a 0.750 D prescription is determined by considering both the prescription strength and the corrective power introduced by the tear lens, which can be calculated using the thin-lens equations to ensure ideal vision correction.
Step-by-step explanation:
To determine the power of a rigid contact lens, one must consider the eye's refractive error and the additional power introduced by the tear lens. The power of a contact lens prescription reflects how much the lens will converge or diverge light to correct the vision problem. In the case of a mildly farsighted person with a prescription of 0.750 D and a near point of 29.0 cm, the power of the tear layer contributes to the overall correction provided by the lens and tear lens system. By employing the thin-lens equations, one can analyze and calculate the ideal corrective power needed by taking both the contact lens and the tear film into account.
The calculation involves understanding that the total corrective power needed ({P_{total}}) is the sum of the contact lens power ({P_{lens}}) and the tear layer power ({P_{tear}}), where {P_{total}} = {P_{lens}} + {P_{tear}}. To ensure an ideal correction, the power of the tear layer needs to be calculated in such a way that the overall system corrects the refractive error perfectly. If a prescription is known, the remaining value of the tear layer can be derived accordingly.