146 SUMMARY OF CURRENT RESEARCHES RELATING TO 



1/4 in., should be supplied with special corrections to render the visual 

 and actinic foci coincident. At the same time it may be stated as an 

 axiom that any objective that will give a clear, well-defined image of 

 an object under the eye-piece, will also produce a sharp and accurate 

 reproduction of the same upon the sensitive plate. He has made 

 most excellent negatives with a French Triplet 1/4 in., costing no 

 more than five dollars, and magnifying 200 diameters — not equal, it is 

 true, to the results obtained with lenses of higher grade and finer 

 corrections, but so good that only a critical eye would discern the 

 difference between them. We quote in full the author's succeeding 

 remarks : — 



" So let not those possessing only cheap instruments be deterred 

 from entering upon this fascinating branch of photography on that 

 account, as their cheap tools will turn out good work with the aid of 

 patience and careful manipulation. Wide angular aperture is not so 

 conducive to good results as a moderate one. Given good corrections 

 of spherical and chromatic aberrations, good penetrating and defining 

 powers, and the objective of moderate aperture will defeat its wide- 

 angled rival on the photographer's field in every encounter. 



" It may safely be asserted that all powers in ordinary use may be 

 successfully employed in photographing by aid of ordinary lamp- 

 light. I have used them all from 4 in. to 1/18 homogeneous 

 immersion ; with, and without amplifiers, and all with equally good 

 results. If a selection has to be made by one just furnishing an 

 outfit, I would suggest a 1 in. or 2/3 ; 1/2 in. or 4/10 ; and 

 1/5 or 1/6. With these and a camera of sufficient bellows capa- 

 city, a range of powers from about 25 to 250 diameters may be 

 obtained, quite sufficient for nine-tenths of the work ever required 

 in this direction. If a higher power be necessary, then a 1/10 

 immersion is recommended. None of these powers from the 1/5 

 upwards will require any special correction. If they define any 

 given object under the eye-piece, clearly and distinctly, it may be 

 accepted as certain that they will produce a correspondingly good 

 photograph of it. But for powers less than 1/4 in., I would earnestly 

 recommend those specially corrected for photography, else sharply 

 defined results cannot be depended upon with any certainty. I 

 have seen objectives of low powers, in which there was no apparent 

 difference between the actinic and visual foci, and which gave — 

 without any further corrections — negatives as sharp as the image 

 seen upon the focusing screen; but such instances are rare, and 

 cannot be 'counted upon. I would therefore reiterate, for all powers 

 lower than 1/4 in., employ only those specially corrected for photo- 

 graphy." 



Photography and Minute Details.* — The following remarks are 

 made by a contemporary on the discussion on this subject at the 

 November meeting. 



" It appears to us that, in these discussions, sufficient allowance 

 is not made for the varying acuteness of vision possessed by different 



* Brit. Joiim. of Phot., xxxii. (1885) pp. 786-7. 



