Achromatic lenses. Achromatic lenses have color correction on main and two additional wavelengths of visible spectral range. Chromatic difference of zoom is not corrected but it can be compensated by so called compensation ocular. Field curvature is not corrected and in the lens especially with small zoom on the edges of field of view the picture is fuzzy. In the marking on rimmed usually there is no signs of optical correction code.
On the lenses of the OptiTech company there can be marking (S) that means that it is achromatic lens with spring mechanisms which protects the specimen from squeezing by the lens of the microscope.
Apochromatic lenses are lenses that have full correction of chromatic aberration but the chromatic difference of zoom and the curvature of field view are not corrected. On its rimmed there is a marking APO.
Plan-achromatic lenses are lenses that have the field curvature corrected, chromatic aberration and chromatic difference are increased. Very useful objective lens for small zooms that gives sharp picture on whole field of view. It is marked as PL, Plan.
Plan-apochromatic lenses is a lenses with full chromatic correction, flat field of view and with corrected chromatic difference of zoom. It is up-to-date and too expensive lens for a microscope. It is marked as Plan-apo.
On the west the so called semi-planates(Semi - Plan) are manufactured. Such lenses are between achromatic and plan-achromatic lenses and the field curvature is reduced (not fully corrected). They are marked by the code SP.
Lets take a thorough look at the markings for lenses to the kids microscopes.
On the lens rimmed there are indications of zoom of the lens, for example 4x, 40x, 100x. To calculate the microscope zoom abilities it is necessary to multiply the zoom of the lens to the zoom of the ocular.
After the lens zoom marking of the microscope through the slash there is an indication of so called numerical aperture (marked by the symbols NA during calculations). Numerical aperture shows the maximum useful zoom that can be got by that lens type and the what resolution the lens has. Maximum useful zoom of a microscope with the presented lens is calculated by the numeric aperture is multiplied on 1000. For example, the lens of the microscope with the numerical aperture 0.65 has useful zoom 650x. To make bigger zoom is not recommended as it will not add clearance of a picture but will lessen the contrast and brightness of a picture. Also the resolution of a lens can be calculated. For that purpose it is necessary to divide the length of the wave in mcmm on the double numerical aperture. Quality immersion lenses with numerical aperture 1.40 give resolution about 0.12mcmm.
Under the zoom and the numerical aperture on the lens of a kids microscope there is some times other parameters. For example, the length of a drawtube of a microscope with which the lenses can work with standard zoom. For example, the usual length of the drawtube is 160mm. Also there is an indication of a thickness of a cover glass with which the lens will work normally, it is usually 0.17 mm.