(_See article on lenses in Part First._)
View lenses may be classed in two groups:
Single combination lenses and double combination lenses.
Single combination lenses are intended for producing pictures of
inanimate objects, in the production of which the time of exposure
is of minor importance. They are of greater focal length than the
double, and, on account of their simple form, are less expensive.
The combination consists of a meniscus, composed of two lenses, one
convergent, the other divergent. The two are cemented together, so
that only two surfaces are presented to reflect light. This lens is
well calculated [p158] for out-door work, but does not give such
roundness of form nor such delicacy and finish as may be obtained by
the double combination. But it has greater depth of focus, and,
having but two reflexive surfaces, fits it peculiarly for views of
foliage, and enables it to work into the green of the landscape more
completely and vigorously.
The single lens is not free from distortion. The marginal rays are
apt to give the barrel-shape figure to the view, but for landscapes
this is practically of little or no consequence.
The smaller sizes of single lenses are more effective than the
larger. They are quicker and have much less distortion, and when
stopped very small have practically none.