Volltext: Carl Zeiss Optische Werkstätte Jena: Microscopes and Microscopical Accessories. No. 29

marginal portions of the field do, therefore, not appear in sharp focus simul¬ 
taneously, but have to be focussed in succession. 
As a result of the great concentration of light afforded by these objectives 
they permit of the use of very high power eye-pieces without detriment to 
accuracy or brightness of the image, thus giving high magnifying power with 
relatively long focal length, thus yielding with the same objective a series of very 
varying amplifications. 
In the annexed list beside the apertures and foci the corresponding obj ective 
magnification is stated, i. e. the magnification which the objective alone would 
give at the distance of distinct vision if used as a simple lens. This is simply 
250 (distance for distinct vision) divided by the focal length of 
the objective in mm. For instance, the objective magnification 
of a 3mm objective is: 
The apertures Indicated are the guaranteed minimum values; the 
stated focal lengths are adhered to as closely as possible. 
Remarks on the use of the 2 mm Apochromatic Lens of 1.40mm aperture 
(homogeneous Immersion). 
Owing both to the hyper-hemispherical form of the front lens, which is held 
in situ by a very narrow ridge at the extreme edge of the setting, and its rela¬ 
tively short working distance (0.2mm) this lens demands careful treatment 
and should, in particular, be scrupulously guarded against shocks or pressure. 
As compared with the 2mm lens of 1.30 aperture this lens possesses a greater 
resolving and defining power in the proportion of 14 : 13 and gives a brighter 
image in the proportion of 20 : 17. The 2mm 1.40 is a decided advantage where 
exceptionally intricate problems requiring the most delicate apparatus 
have to be solved, and also in such cases where the lens is to serve as a means 
of controlling observations made with lower powers; for regular work 
preference should be given, generally speaking, to the 2mm 1.30, owing, to the 
greater firmness of the frontal lens. 
The objective 3mm 1.40 apert. has, however, this advantage over the 2mm 1.40 
that, while possessing the same optical capacity, it has a greater working distance 
and is also less delicate as regards its mechanical construction. 
(Ba-zJ lslVizAi^tcUli} 9etia.


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