Olympus Microscope manual Distortion, Aberration of magnitude, Wavefront Aberration

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OPTICAL TERMINOLOGY

Figure 9-5 Astigmatism and Change in Spot Shape in Different Focus Positions

(a) (b) (c)

(a)

(b)

(c)

(4) Field curvature

An image plane of an object on a plane perpendicular to an optical axis does not always become a plane perpendicular to the optical axis, but it generally becomes a curved plane. This symptom is called “field curvature.”

When field curvature is present, the image is more displaced as it becomes closer to the periphery of the visual field. Therefore, when the center of an image is brought into focus, blur occurs in the peripheral areas of the image. To bring the entire image, including the periphery, into clear focus, it is necessary to adequately compensate for this type of aberration.

(5) Distortion

When there is no similar relation between a planar shape on an object and a shape on the image plane, this is called “distortion.” When distortion is present, a square image appears in a shape of a barrel or pin-cushion as shown in Figure 9-6.

Figure 9-6 Distortion

(a) Barrel shape (a) Pin-cushion

typetype

The microscope optical system contains some distortion. When distortion is present, it can bring erroneous results of shape measurements. When a microscope is used for precision measurements, pay close attention to this aberration, for example, by providing it with an aberration compensation function.

(6) Chromatic aberration

Glasses used for optical systems have different refractive indexes depending on the wavelength. This causes differences in focal length between wavelengths and generates displacement of image forming position. This phenomenon is called “chromatic aberration,” which is sometimes subdivided into axial displacement on the optical axis, called “axial chromatic aberration” (or lateral chromatic aberration) and displacement on the image plane, called “chromatic

aberration of magnitude.”

Many special glass materials are used, e.g., for apochromats (MPlanApo in Olympus), to eliminate chromatic aberration in a wide range from violet light (g-rays with wavelength of 435 nm) to red light (c-rays with wavelength of 656 nm).

9.3 Wavefront Aberration

Since a long time ago, aberrations have been used in “geometric optics,” which considers light as “light rays.” Microscope optical systems are often used for observation of very small specimens at a wavelength level, and sometimes adopt “wave optics,” which regards light as “waves” and handles the phase information, taking account of the influence of diffraction.

In such a case, “wavefront aberration” is used for evaluation. As shown below, when requirements for ideal imaging are satisfied in a microscope optical system, the spherical wavefront (spherical waves) coming from a single point on an object (specimen) is converted to plane waves through an ideal objective lens. The plane waves are converted to spherical waves through an ideal tube lens, and condensed to a single point. The wavefront of these waves is called the “ideal wavefront.”

Figure 9-7 Ideal Microscope Optical System

Specimen Ideal

 

Ideal

Image plane

 

 

objective

 

tube lens

 

 

 

 

lens

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Spherical

Plane

Spherical

wave

wave

wave

Based on the figure indicated for (1) spherical aberration, the behavior of the wavefront in an optical system that has an aberration is described below.

Figure 9-8 Illustration of Wavefront Aberration

 

Actual

 

wavefront

Specimen

Ideal

 

wavefront

Objective lens with

 

spherical aberration

 

A difference (a degree of disagreement) between the ideal wavefront and the actual wavefront shown above is called “wavefront aberration.”

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Contents 0 6 1 Microscope Components GuidePage Contents TLU UIS/UIS2Features of UIS2 objective lenses Observation/single tubes Illumination systems and power supplyFocusing units Video systemMotorized Unit System Diagram UIS2 Mplfln UIS2LCD DIC*1 POLMplfln series Plan SemiApochromatLmplfln series Long WD M Plan SemiApochromatMpln series Plan AchromatLCPLFLN50xLCD LCD Long WD M Plan SemiApochromatLCPLFLN-LCD series LCPLFLN20xLCDSLMPlan series Plan ApochromatSuper Long WD M Plan Achromat MPlanApo seriesLMPlan-IR series/MPlan-IR IR Long WD M Plan SemiApochromat/IR M Plan SemiApochromatMPLFLN-BD series Plan SemiApochromat BDMPLFLN-BDP series Plan SemiApochromat BDPLMPLFLN-BD series Long WD M Plan SemiApochromat BDMPLN-BD series Plan Achromat BDMPlanApo100xBD Focal distance WeightPlan Apochromat BD MPlanApo-BDHole Bxfm frameBXFM-F 32H8BXFM-F+BXFM-ILH+BXFM-ILHSPU BxfmBXFM-F+BXFM-ILHS BXFM-SSZ-STL StandsSZ2-STU2 Universal stand typeBX-URA2 Reflected light illuminator for BF/DFUniversal reflected light illuminator BX-RLA2Than Reflected light illuminators for BFBX-KMA/BX-KMA-ESD LessVery compact reflected light illuminator with reduced depth Reflected light illuminator for BFKmas LH100HG Lamp housingsLH75XEAPO LH100HGAPORCV Lgad SZX-TLGAD Lamp housing accessoriesTH4-HS RMTDulha LG-PS2LG-SF TLU Widefield trinocular observation tubesSingle port tube with lens TR30IRSuper widefield erect image tilting trinocular tube Super widefield trinocular observation tubesSWTR-3 Swetr MX-SWETTRTRU Various accessories for various observation needIntermediate tubes ECAAPT EPA2Eyepieces for UIS2 optical system EyepiecesFilar micrometer eyepiece OSMP4RE Revolving nosepieces for BF objective lensesD6RE D7RE D6RE-ESDBD-M-AD Revolving nosepieces for BF/DF objective lenses5BDRE D5BDRE D6BDRE P5BDRETV0.63xC Mount video port with 0.63x lens Mount video camera portsTV0.35xC-2 TV0.5xC-3 Mount video port with 0.5x lensTmad FMT Video camera mount adaptersVideo camera port CMAD3 BmadBX-RFAA Motorized unitsBX-RLAA+U-D6REMC+U-LH100-3 BX-UCB D5BDREMCD6REMC P5REMCFWR AFA1MActive auto focus unit Iffh Focus adjustment knob unitFocus adjustment knob interface BXFMA-FUVF248LB+U-LH80HGXE Deep ultraviolet observation systemUVF248IM UVF2FB/5FBObservation through eyepiece binocular observation Focal length of tube lensFocal depth formula Visual observation Berek formula = 50 ⋅ 0.5 =352µmMPLFLN100⋅ N.A.=0.90, λ =0.55µm 3355Astigmatism Classification of AberrationsWavefront Aberration DistortionAberration of magnitude Olympus Corporation has obtained ISO9001/14001