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Perfection in miniature:
Microscope objectives for every application. |
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While there is a limited number of condensers available, the very great number of objectives reveals the great diversity of microscopy.
Here, we try to classify the objectives according to their state of optical correction. The two main criteria are the elimination of chromatic errors and the flatness of the intermediate image – which, when perfect, provides an image with edge-to-edge sharpness, even with large fields of view. Furthermore, the objectives can be classified into transmittedlight and reflected-light versions. The first type is always designed for use with cover slips (0.17mm). Reflected-light objectives – with the prefix “Epi-” – feature specially coated glass surfaces to avoid reflection in the optics (“anti-reflection coating”).
All the objectives mentioned here are members of the family of ICS-Optics (ICS: Infinity Color-corrected System). These objectives project their images to “infinity” first. Only the tube lens produces an intermediate image – to be more precise, at a distance of approx. 164.5 mm behind the tube lens. This distance was chosen to comply with the classical tube length.
| These are the main benefits of the ICS optics: |
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- The light rays in these “infinity optics” run parallel between the objective and the tube lens. Filters, reflectors, plane-parallel components can be used without the need for additional optics, which would only be disturbing.
- Objectives and tube lens together produce the final – fully-corrected – intermediate image. Classical microscopes with “finite optics” require the eyepieces to perform a lot of additional compensation work. Hence the name “compensating eyepieces”.
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