Cassegrain lens

Figure 9.25 Optical paths of FTIR microscope with IR radiation (a) transmittance and (b) reflectance. M, mirror C, Cassegrain lens. (Reproduced by permission of PerkinElmer Inc.)...

Figure 5.47 Cassegrain lens in transmission mode (upper frame), reflection mode, and as part of an ATR system (lower frame). 

Cassegrain lens A focusing device that utilizes highly polished mirrors in lieu of glass lenses. 

Some of the new IR microscopes on the market are capable of minimising these problems. An IR-Plan IR microscope (obtained from Spectra-Tech, Stamford, CT) has been used to obtain IR spectra of Kevlar filaments and also to carry out orientation measurements. The microscope uses a 15x IR/visible reflecting lens with Cassegrain optics to focus the IR beam onto the sample (Refleachromat, Spectra-Tech). A lOx reflecting Cassegrain beam condenser is used to collect the transmitted beam after it passes through the sample. The beam condenser also has a sample compensator, which can be used to correct for optical aberrations caused by the fibre samples. The microscope uses its own narrow band liquid... 

The optical design of the spectrometer is presented in fig.l The 1ms B is a field lens. The mirrors D and E are a Cassegrain system (f/20) that collimates the optical beam coming from the telescope. The coUimated beam is reflected on the grating G by the plane mirror F. Finally the camera of the spectrometer (mirrors H and I), focalize the radiation on the detector L. 

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