SOME PROBLEMS IN HIGH POWER PHOTOMICROGRAPHY. 



By R. E. Slade, M.C, D.Sc, F.I.C., and G. t. Higson, M.Sc, 



A. I.e. 



In an investigation of photographic emulsions we have found it 

 necessary to take photomicrographs, using the greatest resolving power 

 which we could obtain. In our attempts to overcome various difficul- 

 ties inherent in different forms of apparatus, we have constructed an 

 apparatus, which we believe contains some novel features. 



The source of illumination is a 100 c.p. " Pointolite " lamp con- 

 tained in a light tight box, a light tight connection being made between 

 this box and the sub-stage condenser of the microscope, which is used 

 in a horizontal position. Although this box is not ventilated we have 

 not been troubled by heat from the lamp. No optical system or heat 

 absorbing cell is interposed between the Pointolite lamp and the con- 

 denser, but an arrangement is fitted for introducing a colour screen in 

 this position. The microscope is used with or without an eye-piece in 



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a room which is totally dark, and the image is projected on to the 

 plate, placed in a holder about one foot from the microscope, no 

 camera being used. The whole apparatus is mounted on a solid block 

 of ash. Focussing is done direct on to a piece of white card placed in 

 the plate holder, a shutter is then brought down just in front of the 

 eye-piece of the microscope, a plate put into the plate holder, and the 

 exposure made. 



This shutter, which is mounted quite separately from the base of 

 the apparatus, consists of a roller blind shutter release, to the teat of 

 which is attached "a flap of black card (see Fig.), which is lifted clear 

 of the path of the light rays by pressing the bulb of the release, ex- 

 posure thus being made with complete absence of vibration. 



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