287 



A SIMPLE METHOD OF PRODUCING STEREO- 

 PHOTO-MICROGRAPHS. 



By \V. P. Dollmax (of Adelaide, South Australia). 



{Bead before the Royal Microscopical Society February 21*/, 190G.) 



Plate 21. 



I will endeavour to put in as concise a form as possible the 

 principal points in the production of the stereo-micrographs 

 which will be shown this evening. I have taken a practical 

 interest in stereoscopic photography since 1865, optical work 

 having always an attraction for me. Some twelve or more 

 months ago a friend called my attention to an article on stereo- 

 photo-micrography (which I had perused at the time of its 

 publication, but had since forgotten) in the British Journal of 

 Photography Almanac for 1894, by the then editor, the late 

 Mr. J. Traill Taylor, who therein explained several methods of 

 producing stereograms of microscopic objects. 



I adopted what I thought the simplest method — that of 

 obscuring by a semicircular shield half of the objective in use. 

 I have a cloth-lined brass tube with one end half-screened 

 (blackened, of course), made to slip over the lens and to revolve 

 smoothly on the mount. As the objectives vary in diameter, 

 the tube was made to fit the widest one, and strips of cardboard 

 were cut to make the tube fit the smaller ones. In the case 

 of photo-objectives (I have used these from 2 to 6-in. focus), 

 a semicircular shield of thin blackened brass can be dropped 

 against the diaphragm between the combinations, and this is 

 certainly the better place for the screen. I have used a 2 -in. 

 Dallmeyer portrait combination (which is specially good for this 

 work), a 4^-in. Unar, and a 6-in. Goerz. I use a f 56 dia- 

 phragm with the Dallmeyer, the same or /8 with the Unar, 

 and /8 with the Goerz. Of course, for low magnifications of a 

 rough object it is advisable to work with a low power (the 4^ -in. 

 focus lens was used for most of the prints exhibited); but for 

 larger objects a 6-in. lens would define better. The little Dall- 

 meyer lens is a marvel for definition and flatness over the small 



