zoom lenses

Why do images presented by a lens have optical aberrations?A. DistortionDistortion will cause real objects to be straight lines, but in photos to be non-straight lines, to be curved lines.a) barrelb) pincushionc) complex/wavyTypes of lenses prone to distortion: usually zoom lenses and wide-angle lenses.B. Field curvatureFor plane objects in reality, after imaging, the real image surface is curved, and most actual sensors are also flat, which will cause the center field of view and the edge field of view to be unable to present clear images at the same time.Lens types prone to field curvature: usually wide-angle lenses and large aperture lenses.C. Vignettinga) Vignetting-----Light FalloffUneven brightness Light Falloff, the exposure of the center field of view and the edge field of view are different, resulting in inconsistent brightness between the center and edge of the picture, which is what we often call the camera vignetting problem.b) Vignetting-----Color CastUsually there is a color difference between the edges of the picture (especially the corners) and the center area. It is not entirely caused by lens aberration, filters and sensors will also have a certain impact.Types of lenses prone to vignetting: usually largeThere are many factors that cause optical aberration in lenses, some of which have been shared above:1) distortion2) field curvature3) Vignetting ---Light Falloff4) Vignetting ---Color CastIn fact, there are some other influencing factors:1) Focus ShiftWhen you reduce the aperture size, the best focus plane will move to the front or back. That is, the aperture size will affect the best focus plane position, which is what we call focus shift.Common lenses that are prone to focus shift: large aperture lenses. When adjusting the aperture, the focus usually needs to be re-adjusted.2) Onion ring bokehThere are some out-of-focus circular rays of light in the optical path of the lens, which is generally caused by a defective lens.Common lenses that are prone to "onionrings": Some large aperture lenses often use aspherical lenses because of the flatness of the surface involved during processing.3) Flare-GhostingWhen there are some abnormal colored patches in the presented image, usually like colored circles or colored blocks of specific shapes, we become ghost images.Common ghost images: zoom lenses, lenses with a large number of lenses, and large-diameter lenses. During processing, try to reduce the aperture as much as possible, or use post-image processing.4) Flare-Internal ReflectionsGenerally speaking, highly reflective objects inside the lens, such as structural parts with too high reflectivity, or dirty lenses in the optical path, etc. In most cases it is caused by workmanship issues.Common internal reflection stray light lenses:especially large aperture lenses, during the production process, you can try to eliminate light, cut off light, block stray light, increase transmittance, and reduce the aperture as much as possible when conditions permit.