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Hector Isaev
Hector Isaev


Conclusions: Pupil responses that differ as a function of light intensity and wavelength support the hypothesis that selected stimulus conditions can produce pupil responses that reflect phototransduction primarily mediated by rods, cones, or melanopsin. Use of chromatic pupil responses may be a novel way to diagnose and monitor diseases affecting either the outer or inner retina.


A polychromatic light source illuminates the surface of the object in question. This light is focused at different distances depending on the wavelength and only the light of a very narrow wavelength range is focused on the surface to be measured, with the remaining light concentrically distributed around this focus point onto a larger area. By determining the wavelength of the focused light, which is reflected back into the optical system, very precise distance measurements are possible at up to 70 kHz and in nanometer resolution. The distance is chromatically coded in the measuring range and the optical probe, which is connected to the sensor unit by an optical fiber, determines the measuring range or focal depth of the spectrum.

We have already seen that most chromatics use a slider to switch between the two sets of reeds, but how these sliders operate can vary. The traditional straight tuning has the two reed plates tuned as explained above. Cross harp, in comparison, has a slider with a zigzag of holes, meaning that the notes are split between upper and lower reed plates when the slider is open or closed. There are some supposed advantages of the latter setup, including greater volume, due to the larger openings, but I struggle to hear or feel any appreciable difference myself.

Above the 200 mark we find chromatics with alternative comb materials, such as the Seydel Saxony, with its aluminium comb, and those with more than 12 holes, such as the 14 hole Suzuki SCX-54 and the 16 hole Hohner Super 64. As the price increases, we start to see more exotic materials, and in some cases, such as with the Hohner ACE 48, unique features such as the VarioSpring and Accoustic Coupling Elements. The Seydel Symphony even comes with a heated case that enables the harp to gently heated to the perfect temperature for playing prior to any performance.

A lens will not focus different colors in exactly the same place because the focal length depends on refraction and the index of refraction for blue light (short wavelengths) is larger than that of red light (long wavelengths).The amount of chromaticaberration depends on thedispersion of the glass.

The use of a strong positive lens made from a low dispersion glasslike crown glass coupled with a weaker high dispersion glass likeflint glass can correct the chromaticaberration for two colors, e.g., redand blue.

An achromat doublet does not completely eliminate chromatic aberration, but can eliminate it for two colors, say red and blue. The idea is to use a lens pair with the strongest lens of low dispersion coupled with a weaker one of high dispersion calculated to match the focal lengths for two chosen wavelengths. Cemented doublets of this type are a mainstay of lens design.

Better correction of chromatic aberration has been achieved than that afforded by the achromat doublets. One could use three lenses to achieve the same focal length for three wavelengths. In practice, so-called apochromatic lenses have been produced in the 4 to 16 mm focal length range for microscope objectives (Pedroti & Pedroti) with the use of fluorite elements.

Another approach to chromatic aberration reduction is to use two positive lenses separated by one half the sum of their wavelengths. Two equal positive lenses are used in eyepieces like the Ramsden eyepiece for correction.

Chromatic aberration is a phenomenon in which light rays passing through a lens focus at different points, depending on their wavelength. There are two types of chromatic aberration: axial chromatic aberration and lateral chromatic aberration.

Lateral chromatic aberration is reduced to some degree by combining different lens elements with different refractive indexes, but optically speaking, it cannot be completely eliminated. In addition to red and its complimentary color cyan, and blue and its complimentary color yellow, some lenses may exhibit complex color fringing that combines these two primary types. It is greatly reduced by low-dispersion ED glass.

Because chromatic aberration is more often seen in images that are shot with wide apertures, using smaller f/stops is one way that you can try to keep your images free from chromatic aberration. Another instance where chromatic aberration is seen is when photographing astrophotography with certain lenses such as the 58mm, and focusing on an object not in the center of the frame.

Axial chromatic aberration is applied to JPG, TIFF and NEF images in Nikon View NX (version 1.3.0 onwards) and with NEFs in Capture NX2 (version 2.2.0 onwards). In addition to the automatic correction, there is a manual adjustment slider. 350c69d7ab


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