Mr. Claudet on a Focus-Equalizer for Photograph*/. 233 



I have found such means ; and it turns out indeed that by my 

 mechanical construction the differential movement can be effected, 

 not only as readily and easily, but with a greater command and 

 steadiness than by moving only one lens. The following is a descrip- 

 tion of the arrangement : — 



Description of the Focus- Equalizer. 



The tube, containing at its two ends the lenses A and B, is divided 

 into two parts, sliding in the principal tube S S S S fixed in the 

 front of the camera at V V. 



Each tube has a strong pin, L and L'. These two pins are intended 

 to push the tubes to and fro from the centre of the combination on 

 the line P P' by means of the mechanical piece N N' N" in the shape 

 of a sextant, having two slits, M M and M' M', cut at an angle of 36°. 

 Now the sextant, being mounted on a sliding bar QQ', fixed in a socket 

 holding to the tube S S S S at P P', can be made to move to and fro 

 on the line P P' by means of a rack and pinion moved by a handle 

 V on the axis R. While the sextant moves in the line P' P, the 

 two slits will act on the two pins, and gradually increase the separa- 

 tion of the tubes ; and on making the sextant move back from P to 

 P', the slits will bring the two pins nearer each other, and decrease the 

 separation of the tubes. 



It will thus be easily understood how we can increase and reduce 

 the separation of the two lenses from the centre of the combina- 

 tion ; but we have now to explain how we can produce the differ- 



sH 



ential movement according to the mathematical formulae calculated 

 by Dr. Sommer. 



The arc of the sextant is divided into 100 parts, in two rows one 

 Phil. Mag. S. 4, Vol. 31. No. 229. Sept. 1867. R 



