4 



HOW TO PHOTOGRAPH 



be performed. If the beginner proposes to 

 limit himself to the photoyrapliy of com- 

 paratively easy objects, lenses of 2-inch, i- 

 incl), -J-inch, |-incb, wi.l suffice. A ^ inch 

 of wide angle will be found capable of re- 

 solving the majority of test objects satisfac- 



torily. A 5-inch or 4-inch will be found 

 very useful for photographing large objects, 

 such as whole insects, wood sections, and 

 anatomical preparations; while if the stu- 

 dent requires a few liigli powers, and can- 

 not affoid the expensive ones of the best 



LEG OF WATER BOATMAN (nOTONECTa). 



Taken with a Ross 4-inch. 



English makers he will find the moderate 

 priced immersion lenses of Seibert equal to 

 ail the work that will generally be required 

 of them. These lenses are sold by Baker, 

 of liolborn. Immersion lenses are special- 

 ly useful in photography, as they admit a 

 vast amount of light, and are, therefore, 

 very rapid in action. 



Some lenses are not well suited to pho- 

 to micrography, ihcir visual and aclinic foci 

 not being coincident ; that is, when an ob- 

 ject is focussed accurately on the screen of 

 the camera, and a photograph taken, the 

 picture will be indistinct and blurred, owing 

 to the fact that the rays forming the visual 

 ima^e do not lie in the same plane as those 

 forming the photographic image. Such 



lenses /nay be used for photography, by 

 making experiments and determining the 

 amount of allowance fur this difference to 

 be made when focussing; but it is far more 

 satisfactory to use lenses which do not re- 

 quire sucli correction. The writer has 

 used lenses by Ross, Wale, Swift, and Sie- 

 bert, an 1 the visual and actinic foci were 

 coincident in all such as he has used. 



Much difference of opinion prevails as to 

 whether the eye-piece should or shoul 1 not 

 be used in photo-micrography. Same as- 

 sert that the eye-piece spoils good defini- 

 tion. This is possible with a bad eye- 

 pece; but the writer has for years used the 

 e)e-piece when pliotographing with low 

 powers, and l.as found 10 difficulty in ob- 



