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| Some requirements of the preparations |
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| Are the objective and the specimen clean? |
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A fingerprint on the front lens of an air objective alone may be sufficient to affect the high-contrast reproduction of a specimen since scattered light is produced. The same applies to immersion objectives soiled with residues of resin or emulsions (e.g. oil and water). Such cases require careful cleaning using a soft cloth and pure alcohol.
| Do the cover slips have the correct thickness? |
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It is very important that cover slips for objectives of a high aperture used without immersion oil have the standard thickness of 0.17 mm, since here the cover slips are already taken into consideration in the complicated computation of objectives. Therefore, if a different thickness than the standard one is used, the quality of the optical image suffers visibly in the case of high apertures. Experience has shown that the following deviations are just acceptable and no more:
± 0,01 mm bei N.A. > 0,7
± 0,03 mm bei 0,3 < N.A. < 0,7 |  |
| Do you use the correct immersion oil? |
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Most high-performance objectives from Carl Zeiss are used with immersion oil. The right oil with the refractive index n = 1.51 and a suitable oiler are supplied with the objective. The oil is PCB-free and exhibits scarcely any autofluorescence. The image will be markedly impaired if air bubbles are contained in the immersion layer. To avoid these bubbles, it is vital to apply the oil in the right way. The operating instructions include the relevant hints.
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