Infinity correction

It is advantageous if the microscope objective is designed to work with collimated beams. Such objectives are called infinity corrected . 

The principle of a confocal microscope is illustrated by Figure 11.9, by comparison to a conventional, infinity-corrected microscope. Light scattered from two sample depths, Z] and zi, is indicated by the solid and dashed lines. 

Advanced microscopes made since 1980 have a more complicated optical arrangement called infinity-corrected optics. The objective lens of these microscopes generates parallel beams from a point on the object. A tube lens is added between the objective and eyepiece to focus the parallel beams to form an image on a plane, which is further viewed and enlarged by the eyepiece. 

The manufacturers of infrared microscopes are split almost evenly between those that produce infinity-corrected and those producing non-infinity-corrected microscopes. Infinity correction effectively refers to a coUimation of the beam throughout the microscope (other than at the condenser and objective outputs), and is frequently used in research-grade optical microscopes. Despite the added... 

Figure 1.17 (a) Visual image of a 1 im-diameter polystyrene bead. The lower images show Raman images of the bead, recorded with a lOOx (NA = 0.95) infinity-corrected microscope objective at increments of (left to right) 1.0, 0.5 and 0.1 pm per step, respectively (b) Raman spectrum measured from the center of one of these beads. Reproduced with permission from Ref [41]. 

Every microscope is characterized by its numerical aperture NA, which describes the angle between the optical axis and the most remote point of the sample which can be observed. NA is directly proportional to the energy throughput. Objectives with infinity correction provide advantages such as sharper images and better sig-nal-to-noise ratio. Infinity corrected objectives are increasingly used, especially in microscopic imaging with array detectors. 

Recent designs make use of the infinity corrected system, which provides greater versatility in adapting the microscope to new techniques. In this system, the specimen lies precisely in the front focal plane of the... 

The/number for the most common infinity-corrected microscope objective lens is given by... 

Modern objectives are of the infinity corrected type, meaning that the image plane is at infinity (see Figure 3.19). Light collected by an infinity corrected objective is thus emitted as a collimated beam (sets of parallel rays) offering the... 

Shortpass dichroic mirror, custom piece (e.g. 488DSCX, Chroma Technology Corp., USA) Microscope objective X100,1.45 NA infinity corrected oil immersion (Plan Fluar, Zeiss, Germany)... 

OBJ Microscope objective XI00,1.45 NA infinity corrected oil immersion (Plan Fluar,... 

A simple, infinity-corrected optical microscope with an electronic detector is shown schematically in Fig. 1. The parallel rays in this type of microscope make it easy to insert additional optical elements into the beam path and are now used in most Raman microscopes. The object is placed in the focal plane of the microscope objective and the magnified image is formed on a detector placed in the focal plane of the tube lens the resulting... 

Figure 1 Schematic diagram of an optical microscope with an infinity-corrected microscope objective of focal length /o and a back aperture diameter D. The tube lens of focal length / focuses the light on an electronic detector such as a CCD.

The MTF of an imaging system is the product of the constituent MTFs for all the components of that system, including the diffraction-limited MTF. The diffraction-limited MTF can be calculated using Eq. (6), where f is the spatial frequency in line pairs per millimeters and is the cutoff frequency = 1/AFN, where A is the wavelength of interest and FN"" is the infinity corrected/-number) ... 

FT-IR spectrometers specifically manufactured for reflection microspectrometry are commercially available. Such spectrometers can be combined with most microscopes having infinity-corrected optics (in which the output from the Cassegrain objective mirror becomes parallel radiation). Since, in the infinity-corrected design, the output... 

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