_Wanted, a simple Test for a good Lens._--As all writers on Photography
agree that the first great essential for successful practice is a good
lens--that is to say, a lens of which the visual and chemical foci
coincide--can any of the scientific readers of "N. & Q." point out any
simple test by which unscientific parties desirous of practising
photography may be enabled to judge of the goodness of a lens? A country
gentleman, like myself, may purchase a lens from an eminent house, with an
assurance that it is everything that can be desired (and I am _not_ putting
an imaginary case), and may succeed in getting beautiful images upon his
focussing-glass, but very unsatisfactory pictures; and it may not be until
he has almost abandoned photography, in despair at his own want of skill,
that he has the opportunity of showing his apparatus, manipulation, &c. to
some more practised hand, who is enabled to prove that _the lens was not
capable_ of doing what the vendors stated it could do. Surely scientific
men must know of a simple test which would save the disappointment I have
described; and I hope some one will take pity upon me, and send it to "N. &
Q.," for the benefit of myself and every other