![]() ![]() Mind you, the minimum is fairly shallow, so you can vary the shape factor a fair amount without grossly increasing the spherical aberration. or by combining Equations ( 5 ) and (6): The spherical aberration of the whole eye is the sum of the Seidel spherical contributions from each refracting surface or refracting. The radii of curvatures of the lens must satisfy equation 4.2.7 as well as q 0.38 (4.2.8) 1 f ( n 1) ( 1 r 1 1 r 2), so that, for f 20 cm and q 0.38, the radii of curvature for least spherical aberration should be r 1 17.4 cm and r 2 38.7 cm. Seidel sums are given below 12: Spherical aberration. It is seen that the aberration is least for a shape factor of about q 0.38. Of course, you have to use the lens the right way round! If you turn it round, or if light is coming in from the right, the shape factor is 0.38, and the spherical aberration is not at a minimum. The resulting total Seidel spherical aberration of the whole eye cannot be made zero unless the cornea has an asphericity much higher than the population mean. Primary aberrations which are also called fourth order wave aberrations in terms of. So that, for \(f\) = 20 cm and \(q\) = −0.38, the radii of curvature for least spherical aberration should be \(r_1\) = 17.4 cm and \(r_2\) = −38.7 cm. The five Seidel aberrations are: Spherical Aberration: this is the aberration affecting rays from a point on the optical axis because rays from this point going out in different directions pass through different parts of the lens, then, if the lens is spherical, or otherwise not the exact shape needed to bring them all to a focus, then these rays will not all be focused at the same point on the other side of the lens.
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