23 
Huyghenian Eye-pieees. 
We supply these for use with the ordinary achromatic objectives. Their 
focal lengths and magnifications are shown in the following table. 
Eye-piece No. 
1 
3 
3 
4 
5 
Focus in mm 
50 
40 
30 
25 
20 
(Eye-piece) magnification 
3 
4 
5.5 
7 
9 
Price 7 Marks each. 
The magnification is computed by the same rule as in the compensating 
series (see page 10), the varying position of their lower focal planes being, 
however, taken into consideration. 
With regard to the selection of eye-pieces for a microscope we would remark, 
that all our achromatic objectives are capable of still giving effective magnifications 
for regular observation with Ocular 4, good illumination being understood in the 
case of the highest powers. 
We no longer supply the "orthoscopic" eye-pieces of former catalogues, as 
they are greatly inferior to the compensating and projecting oculars. 
Respecting the use of Compensating Oculars with achromatic objectives 
vid. p. 20. 
We do not supply Huyghenian Oculars for the long (English) 
tube. 
Oculars for special purposes (Micrometer-. Spectroscopic and others) vid. 
No. 28—30 and 52—55. 
