Distortion Other than distortions from lens imperfections, certain distortions occur from the geometry of the lens. The barrel and pincushion distortions below can be readily seen in the image formed by a thick double convex glass lens. They are the reason for a practical limitation in the magnification achievable from a simple magnifier. These distortions are mimimized by using symmetric doublets such as the orthoscopic doublet and eyepieces such as the Ramsden eyepiece. Lens Aberrations

Index Lens concepts "Reference Meyer-Arendt Ch 5

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Curvature of Field Curvature of field causes an planar object to project a curved (nonplanar) image. It can be thought of as arising from a "power error" for rays at a large angle. Those rays see then lens as having an effectively smaller diameter and an effectively higher power, forming the image of the off axis points closer to the lens. Lens Aberrations	Index Lens concepts "Reference Meyer-Arendt Ch 5
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