Producing Stereo- Photomicrographs. By W. P. Dollman. 259 



An important thing to remember when photographing opaques, 

 is that, to secure even illumination of the two halves, the illu- 

 minant must be on the same level as the centre of the objective. 

 For the lighting of large transparent objects, when using the 4^-in. 

 and 6-in. objectives, I have had a cell, which carries a 4£, 6, or 8-in. 

 focus uncorrected condenser, fitted to the large aperture under the 

 main stage of the Microscope, and brought as near as possible to the 

 object. For the smaller objects I use an achromatic condenser of 

 1 • N". A. This can be altered in power by removing the top 

 combination, or, if necessary, using only the lower of the three 

 lenses. As illuminant, I use acetylene (the finest light for all 

 ordinary work), from a special burner I had made, limelight, and 

 sometimes sunlight (parallel rays), through a heat - absorbing 

 medium. On the platform carrying the apparatus I have marked 

 a scale from to 49 in., with the zero at the level of the Micro- 

 scope stage. This, with the aid of tables for the various lenses 

 used, enables me to work to definite magnitudes, and also to 

 calculate approximately the focus of all objectives that can be used 

 without an eyepiece. 



By the way, low power micro-objectives are almost invariably 

 very wrongly named — a nominal 3-inch being only 2 ' 3-inch, a 

 so-called 2-inch only 1 ' 5, and so on. I do not think I need say 

 anything about exposure, as that depends upon colour or brightness 

 of object, illumination and magnification. I use ordinary developers, 

 such as would be suitable for landscapes, using such as would give 

 hard results to accentuate feeble contrasts. Chromatic plates, 

 with or without a yellow screen, are used, and where suitable a 

 malachite green light filter when monochromatic light is desirable. 

 A good deal of my apparatus is makeshift — that is, diverted from 

 other uses — but is effectual. My optical outfit is of the best, both 

 in low and high powers, condensers, etc. 



In this description I fear I have been rather diffuse, and 

 have detailed a lot that perhaps everybody knows all about ; but 

 I thought it expedient, owing to my great distance from the place 

 where this will be read, to be a little particular. 



I ought to have mentioned before, but forgot till I thought I 

 had finished, that (as the major conjugate focus is being used) all 

 non-symmetrical photographic lenses, such as " Unars," " Stig- 

 matics," and portrait combinations, should be reversed on the 

 Microscope (the front combination being presented to the plate), to 

 enable them to perforin at their best. 



North Adelaide, 



South Australia. 



s 2 



