Achromaticlens for telescope

OCT technology has advanced to include a range of new features; for example, Polarization-Sensitive OCT (PS-OCT), which leverages the polarization properties of light to provide vital insight into tissue birefringence and structural characteristics.

TD-OCT employs a moving reference mirror to enable depth scanning, while SD-OCT uses a spectrometer to enable simultaneous depth information capture, therefore improving signal-to-noise ratios and imaging speeds.

202488 — The focal length is the distance between the lens and the point where light converges, which determines perspective, composition, and overall aesthetic.

Although the primary chromatic aberration may be corrected, a residual chromatic error often remains and is called the secondary spectrum, which is the difference between the ray intercepts in \(d\) and \(c\).

Two additional solutions are possible by reversal of the glasses. These two classes of designs are denoted as crown-in-front and flint-in-front designs. Depending upon the particular design requirements, one should examine all four configurations to select the most appropriate.

Edmund Opticsachromatic doublet

The resultant power of two thin lenses in close proximity, \(s_2\rightarrow0\), is \(\phi_{ab}=\phi_a+\phi_b\) and the transverse primary chromatic aberration \(\text{TPAC}\) is

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The system emits light, usually in the near-infrared spectrum, which is then divided into optical and reference beams. The optical beam interacts with the tissue, creating interference patterns. These patterns are processed to reconstruct detailed cross-sectional images of the tissue.

OCT Angiography (OCTA) is an extension of OCT that facilitates non-invasive blood vessel imaging. OCTA leverages the motion contrast of flowing blood cells, using this to generate en-face images of the vasculature without the need for contrasting agents.

Achromaticaberration

The singlet lens suffers from axial chromatic aberration, which is determined by the Abbe number \(V\) of the lens material and its \(\text{FN}\). A widely used lens form that corrects this aberration is the achromatic doublet as illustrated in Fig. 19.

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Figure 20(b) shows an F/5 airspaced doublet using a relatively new pair of glasses that have a small \(P_a-P_b\) and a more typical \(V_a-V_b\). Both the primary and secondary chromatic aberration are well corrected. Due to the relatively low refractive index of the crown glass, the higher power of the elements results in spherical aberration through the seventh order. Almost no spherochromatism (variation of spherical aberration with wavelength) is observed. The 80 percent blur diameter is almost the same for both lenses and is 0.007.

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As the lenses are separated by a distance \(s_d\), the power of the flint or negative lens increases rapidly. The distance \(s_d\) may be expressed as a fraction of the crown-lens focal length by \(p=s_d/f_a\). Requiring the chromatic aberration to be zero implies that

By analyzing changes in the OCT signal over time, it is possible to create detailed maps of the vascular network, which are key to performing perfusion evaluations and identifying vascular abnormalities.

Figure 20(a) illustrates an F/5 airspaced doublet that exhibits well-corrected spherical light and primary chromatic aberrations and has notable secondary color. The angular secondary spectrum for an achromatic thin-lens doublet is given by

This information allows users to effectively visualize nerve bundles, collagen fibers, and other polarizing tissue structures.

OCT has as a wide range of applications in various medical fields, particularly in ophthalmology, where it has revolutionized the diagnosis and management of retinal diseases such as AMD.

Axial resolution is a critical factor in determining the quality of OCT images. It defines the system’s capability to distinguish between structures along the depth or axial direction. With resolutions reaching the micrometer range, OCT systems are adept at providing intricate visualizations of tissue layers and microstructures.

Three basic configurations are used. These are the cemented doublet, broken contact doublet, and the widely airspaced doublet (dialyte). The degrees of freedom are two lens powers, glasses, and shape of each lens.

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Achromatic DoubletThorlabs

The bending or shape of a lens is expressed by \(c=c_1-c_2\) and affects the aberrations of the lens. The bending of each lens is related to its power by \(c_a=\phi_a/(n_a-1)\) and \(c_b=\phi_b(n_b-1)\).

Correction also redistributes an image's resolution; with pincushion removal, the edges will appear slightly sharper (at the expense of the center), whereas ...

Since the two bendings can be used to correct the third-order spherical and coma, the equations for these aberrations can be combined to form a quadratic equation in terms of the curvature of the first surface \(c_1\). Solving for \(c_1\) will yield zero, one, or two solutions for the first lens. A linear equation relates \(c_1\) to \(c_2\) of the second lens.

Achromatic doubletformula

A relay lens system is used to convey the image of the object to the eye or, in some cases, to camera and video sensors. A basic compound microscope could ...

At the heart of OCT is low-coherence interferometry. An OCT system includes essential components such as a light source, a beamsplitter, reference and sample arms, and a detection system.

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When the peak lies in the positive spherical aberration region, two solutions with zero spherical aberration exist in which the solution with the smaller value of \(c_1\) is called the left-hand solution (Fraunhofer or Steinheil forms) and the other is called the right-hand solution (Gaussian form).

Shanghai Optics. "Optical Coherence Tomography (OCT) in medical imaging: Capabilities and key applications". News-Medical. 23 November 2024. .

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The capabilities and uses of OCT are continually expanding, significantly enhancing our understanding and management of various medical conditions. For those interested in exploring how OCT can be integrated into their projects, a free consultation or a quote is available through Shanghai Optics’ contact page.

What is anachromaticlens used for

Achromatic doubletmeaning

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The spherical aberration curve can be raised or lowered by the selection of the \(V\) difference or the \(n\) difference. Specifically, the curve will be lowered as the \(V\) difference is increased or if the \(n\) difference is reduced. As for the thin singlet lens, the coma will be zero for the configuration corresponding to the peak of the spherical aberration curve.

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Achromatic doubletlenses

Shanghai Optics. (2024, July 04). Optical Coherence Tomography (OCT) in medical imaging: Capabilities and key applications. News-Medical. Retrieved on November 23, 2024 from https://www.news-medical.net/whitepaper/20240703/Optical-coherence-tomography-(OCT)-in-medical-imaging-Capabilities-and-key-applications.aspx.

High-resolution images of the retina provided by OCT enable precise identification of drusen, retinal pigment epithelial detachments, and fluid accumulations, aiding in the timely diagnosis and ongoing monitoring of AMD.

While maintaining the achromatic correction of a doublet, the spherical aberration as a function of its shape (\(c_1\)) is described by a parabolic curve. Depending upon the choices of glasses, the peak of the curve may be above, below, or at the zero spherical aberration value.

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The typical dialyte lens suffers from residual secondary spectrum; however, it is possible to design an airspaced achromatic doublet with only one glass type that has significantly reduced secondary spectrum.

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For \(f_{ab}\lt0\), the lens can be made rather compact and is sometimes used as the rear component of some telephoto lenses.

In general, the ratio \((P_a-P_b)/(V_a-V_b)\) is nearly a constant which means little can be done to correct the \(\text{SAC}\). A few glasses exist that allow \(P_a-P_b\approx0\), but the \(V_a-V_b\) is often small, which results in lens element powers of rather excessive strength in order to achieve achromatism.

An achromatic lens has equal focal lengths in \(c\) and \(f\) light. This lens comprises two lens elements where one element with a high \(V\)-number (crown glass) has the same power sign as the doublet and the other element has a low \(V\)-number (flint glass) with opposite power sign.

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Shanghai Optics. 2024. Optical Coherence Tomography (OCT) in medical imaging: Capabilities and key applications. News-Medical, viewed 23 November 2024, https://www.news-medical.net/whitepaper/20240703/Optical-coherence-tomography-(OCT)-in-medical-imaging-Capabilities-and-key-applications.aspx.

Shanghai Optics. "Optical Coherence Tomography (OCT) in medical imaging: Capabilities and key applications". News-Medical. https://www.news-medical.net/whitepaper/20240703/Optical-coherence-tomography-(OCT)-in-medical-imaging-Capabilities-and-key-applications.aspx. (accessed November 23, 2024).

When the separation between the lens elements is made a finite value, the resultant lens is known as a dialyte and is illustrated in Fig. 21.

When \(f_{ab}\gt0\), then \(p\) must be greater than unity, which means that the lens is quite long. The focal point lies between the two lenses, which reduces its general usefulness. This type of lens is known as the Schupmann lens, based upon his research in the late 1890s. Several significant telescopes, as well as eyepieces, have employed this configuration.

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Optical Coherence Tomography (OCT) is a leading-edge imaging technology that is transforming medical diagnostics and research. It provides high-resolution cross-sectional images of biological tissues, enabling detailed analysis and visualization of structures, especially blood vessels.

The addition of Optical Coherence Tomography Angiography (OCTA) has further enhanced the precision and informativeness of blood vessel imaging. This article explores the key components and capabilities of OCT systems, their diverse applications, and their significant impact on diagnosing and managing diseases such as age-related macular degeneration (AMD) and macular edema.