1. The core principle of focusing
The working distance of high magnification lens of achromatic objective lens (e.g. 40x, 100x) is very short, and it is easy to break the objective lens or slide by focusing directly with the high magnification lens. Take x40 objective lens as an example, the correct operation should strictly follow the 'three-step method': firstly, adjust the sample with low magnification (4x or 10x) to make it clear and move it to the centre of the field of view; slowly rotate the converter to switch to high magnification, at this time, the objective lens is close to the focal point; and only use the micro-focusing screw to adjust the focus finely, while the coarse focusing screw may be moved too much, resulting in the impact on the slides. may be bumped by moving it too far. This step is the basis for protecting the x40 objective lens. Many novices neglect the transition to low magnification, resulting in scratches on the lens or broken slides.
2. Oil specification and cleaning points
100x achromatic objective lenses are mostly oil-immersed (labelled 'Oil'), the principle of which is to reduce the refraction loss of light and improve the resolution by using special microscope oil. When operating, it is necessary to pay attention to the fact that other grease can never be used to replace the microscope oil, otherwise it will seriously affect the imaging and even corrode the lens; it is strictly prohibited to use the oil-immersed objective lens as a dry lens, otherwise the image will be blurred. Immediately after use, you must use lens paper dipped in a special cleaning solution to wipe the front of the objective lens, if the oil dries up, not only the difficulty of cleaning increases dramatically, but also may damage the coating, which is the most easy to ignore the maintenance of the novice link.
3. Coverslip thickness
X40 objective lens has been designed to fit a 0.17mm thick coverslip. If you use too thick or too thin slides, it will lead to light refraction deviation, resulting in 'spherical aberration' and blurred images. Beginners need to recognise the standard thickness when purchasing, the laboratory commonly used specifications are mostly 0.17mm ± 0.01mm, this detail directly affects the clarity of the image, many newcomers to the use of non-standard slides repeatedly focusing to no avail, in fact, is to ignore the design parameters of the objective lens.
