BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:LENS ABERRATION YOU SHOULD KNOW - Speaker to be confirmed
DTSTART:20220225T110000Z
DTEND:20220225T120000Z
UID:TALK170822@talks.cam.ac.uk
CONTACT:SimonJT - deleted
DESCRIPTION:An image created by an ideal photographic lens must have the f
 ollowing characteristics:\n\n1) a dot must be formed as a dot\;\n2) a plan
 e (such as a wall) perpendicular to the optical axis must be formed as a p
 lane\;\n3) the image formed by the lens must have the same shape as the ob
 ject itself.\nIn addition\, in terms of image expression\, the lens must s
 how the true color of the reproduced object. Almost perfect lens performa
 nce is only possible if only light rays entering the lens near the optical
  axis are used\, and if the light is monochromatic (light of only one spec
 ific wavelength). However\, in the case of a conventional lens\, where a 
 large aperture is used to obtain sufficient brightness and the lens must b
 ring together rays passing not only near the optical axis\, but from all p
 arts of the image\, it is extremely difficult to create the above ideal co
 nditions due to the existence of the following interference:\n\n1) Because
  most lenses are built only from lenses with spherical surfaces\, the rays
  of light from one point of the object are not displayed as an ideal point
  in the image. (A problem that cannot be avoided with spherical surfaces.
 )\n2) Different types of light (i.e.\, different wavelengths) have differe
 nt focal point positions.\n3) There are many requirements associated with 
 changes in the angle of view (especially in zoom lenses and telephoto lens
 es).\nThe general term used to describe the difference between an ideal an
 d a real image under the influence of the above factors is "aberration". 
 Thus\, in order to design a high-quality lens\, the aberration must be ver
 y small\, and the highest goal should be to obtain an image as close to id
 eal as possible. In general\, aberrations can be divided into two broad c
 ategories: chromatic aberrations\, which occur due to differences in wavel
 engths\, and monochromatic aberrations\, which occur even at a single wave
 length.\n\n*Lens aberrations*\n\n\nAberrations visible in the continuous s
 pectrum	\nChromatic aberrations\n\n- Longitudinal aberration (longitudina
 l chromatic aberration)\n- Cross-sectional chromatic aberration (transver
 se chromatic aberration)\n\n\n\n\nAberrations visible at specific waveleng
 ths\n\n"Five aberrations of Seidl":https://telegra.ph/5-lens-aberrations-t
 hat-occur-with-monochromatic-light-02-25\n\nSpherical aberration\nComa\nAs
 tigmatism\nField curvature\nDistortion\n\n\n*Chromatic aberration*\nWhen w
 hite light (light consisting of many colors mixed evenly so that the eye d
 oes not distinguish any specific color and thus perceives the light as whi
 te)\, such as sunlight\, passes through a prism\, a rainbow spectrum can b
 e observed. . This phenomenon occurs because the prism's refractive index
  (and dispersion intensity) varies with wavelength (short waves are refrac
 ted more intensely than long ones). Although it is most visible in a pris
 m\, this phenomenon also occurs in photographic lenses\, and since it occu
 rs at different wavelengths\, it is called chromatic aberration.\n\nThere 
 are two types of chromatic aberration: "longitudinal chromatic aberration"
 \, in which the position of the focal point on the optical axis varies wit
 h wavelength\, and "chromatic magnification difference"\, in which the ima
 ge magnification in peripheral areas varies with wavelength. In real phot
 ographs\, longitudinal chromatic aberration appears as color blur or flare
 \, and chromatic magnification difference appears as color fringing (when 
 color is visible at the edges).\n\nChromatic aberration in a photographic 
 lens is corrected by combining different types of optical glass with diffe
 rent refractive and dispersion characteristics. Since the effect of chrom
 atic aberration increases at longer focal lengths\, precise correction of 
 chromatic aberration is especially important in super-telephoto lenses in 
 order to obtain good image sharpness. Although there is a limit to the am
 ount of correction allowed by optical glass\, results can be greatly impro
 ved with an artificial crystal such as fluorite or UD glass.\n\nChromatic 
 magnification difference can be called "transverse chromatic aberration" (
 because it occurs across the optical axis).\n\nNote: While chromatic aberr
 ation is most noticeable when using color film\, it also affects black and
  white images\, manifesting itself as a decrease in sharpness.\n\nApochrom
 at (apochromatic lens)\n"Apochromat":https://www.dzoptics.com/en/apochroma
 t-achromat\, also called APO means lens that corrects chromatic aberratio
 n for three wavelengths of light\, the aberration being reduced to a large
  extent\, especially in the secondary spectrum. An electronically focused
  supertelephoto lens is an example of an apochromatic lens.\n\nAchromat (a
 chromatic lens)\nA lens that corrects chromatic aberration for two wavelen
 gths of light. When it comes to photographic lenses\, these two correctab
 le wavelengths are in the blue-violet and yellow ranges.
LOCATION:Venue to be confirmed
END:VEVENT
END:VCALENDAR