Microscope Systems And Their Application in Machine Vision

1 1 Agenda

• What is a microscope system? • Basic setup of a microscope • Differences to standard lenses • Parameters of microscope systems • Illumination options in a microscope setup • Special contrast enhancement techniques • Zoom components • Real-world examples What is a microscope systems?

Greek: μικρός mikrós „small“; σκοπεῖν skopeín „observe“

Microscopes help us to look at small things, by enlarging them until we can see them with bare eyes or an image sensor. A microscope system is a system that consists of compatible components which can be combined into different configurations We only look at visible light microscopes We only look at digial microscopes  no eyepiece but an image sensor in the object plane The optical magnification is ≥1 Basic setup of a microscope microscopes always show the same basic configuration: Sensor Tube lens: - Images onto the sensor - Defines the maximum sensor size

Collimated beam path (infinity conjugated)

Objective: - Images to infinity - Holds the system aperture - Defines the resolution of the system Object Differences to standard lenses

microscope Finite-finite lens Sensor Sensor

Collimated beam path (infinity conjugate)

EnthältSystem apertureSystemblende

Object Object Differences to standard lenses • Collimated beam path offers several options - Distance between objective and tube lens can be changed . Focusing by moving the objective without changing any optical parameter . Integration of filters, mirrors and beam splitters . Beam deflection with mirrors as needed . Integration of a zoom module for magnification variation - Parallel beams give better results with dichroic filters - Coaxial illumination can be integrated efficiently • Often more complex than finite-finite lenses Kenngrößen von microscope systems

• Objective - Magnification: ratio of object and image size - NA (numerical aperture): defines the achievable resolution, comparable to f/# - Working distance: distance between object and objective - Object size (Field-of-View): defines what the sensor sees • Tube lens - Magnification: ratio of object and image size • System

- System magnification = magnificationobjective x magnificationtube-lens - System magnification = focal lengthTube-lens / focal lengthobjective - Maximum Sensor size = Object size x system magnification Illumination options in a microscope setup Sensor • Brightfield illumination - coaxial brightfield illumination with beam splitter in the collimated regime - Köhler illumination possible  optimum homogeneity • Dark field illumination - With ring light - Through-the-lens possible with central aperture • Backlight - Classic illumination in microscopy - Aperture of objective must be filled entirely

Object Special contrast enhancement techniques Sensor • Polarisation - polariser and analyser under 90° to each other („crossed“) - Non-polarizing sample looks black analyser - Inspection of birefringent (optical anisotrope) material - Crystals - Plastics (birefringence)

polariser

Object Special contrast enhancement techniques Sensor • Differential Interference Contrast (DIC) Visualisation of different optical - analyser distances - Inspection of transparent materials - Inspection of glue - Pseudo-3D effect due to relief-like images

polariser

Nomarski image: conductive particles in Chip-on-Glass bond Prism Object Zoom-Components in Mikroscopes

Zoom-components in collimated beam Sensor - Inifinity conjugate on both sides - Large zoom ratios possible (12.5:1) - Parfocal: object stays in focus during zooming

Source: Wikipedia

Object Real world examples

2 microscope systems by Qioptiq

Optem Fusion mag.x system 125 Optimized for Maximum Flexibility Maximum image quality large FOV Resolution power ~3MPixel ~50MPixel Zoom Yes No Compatible to standard Yes No microscope objectives Parfocal distance 95mm 125mm Maximum Sensor size with 2/3“ 25mm Diagonal 1x Tube (11mm Diagonal) Autofocus Possible Available as standard components Real world example 1

Multispectral microscope with Zoom - 3 Spectral ranges by using dichroic beam splitters . 450…660nm . 670…780nm . 800…980nm - 7:1 Zoom ratio - Optical magnification 0.84x… 5.8x - Integrated manual focus

Application: medical research Realized using Optem Fusion components Real world example 2

Differential Interference Contrast • Wide field microscope system mag.x 125 - Integrated DIC-Module - Rotating polarizer - 5mm FoV - Maximum 57mm sensor size - 50MPixel resolution power

Image: Micro lens array R~2 mm, 300 µm pitch Last slide

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