HOW TO PHOTOGRAPH MICROSCOPIC ORJECTS. 
57 
obtained gives a most perfect surface, and the finest definition 
may be distinguished upon it with ease. 
Microscope . — Microscopes are, of course, endless in variety, 
and it would be digressing too far from my subject to enter on 
any description here of those supplied by different makers. The 
one we have used is a Smith & Beck, with stage, sub-stage, 
and rack movements ; but a good lens is the really essential 
part, all else may be supplied with the aid of a little skill and 
ingenuity. Screw stage-movements, however, are of very great 
assistance, and I scarcely see how they can be dispensed with 
altogether when fine work is attempted with a high objective. 
Supposing an instrument resembling that in the plate at H, the 
whole should be mounted on a light block (U), at such a height 
that, when levelled horizontally, and accurately centered, a light 
thrown through the lens of the object-glass may form a rounded 
disc in the centre of the focussing screen at all lengths of the 
camera. If the eye-piece is to be removed — and we have always 
found it advisable, even at the expense of working at a longer 
camera — a tube of black velvet must be introduced into the 
body of the microscope in place of the draw tube, together with 
one or two diaphragms (D) cut out of tin, and carefully coated 
with black. 
No care should be spared in obtaining perfect blackness 
within the camera. Stray light from any reflecting point will 
give the greatest trouble ; and this source of fogging may 
escape notice for a long time if all is not made secure before the 
commencement of regular work. 
The Lens . — I have said that the lens should be a good one, and 
some explanation will be needed on this point, for the qualities 
most prized by the microscopist are not always those which are 
most useful in photographic work. For the latter, the older lenses 
with small angle of aperture and great penetration are for all 
ordinary objects preferable to the most recent improvements 
with large angle and perfection of definition in a flat field : a 
fair definition over the whole picture is of more value than the 
minutest detail over a few isolated points which happen to lie 
in a common plane. Keeping this in view, it will further be 
advisable to use the lowest power which will give the required 
detail, and to sacrifice light by lengthening the camera rather 
than run the risk of losing the penetration which the lower ob- 
jective will afford. But whatever the lens, it will still be im- 
perfect for photographic purposes, as I shall presently explain, 
and this imperfection will be found to vary inversely as the 
power of the objective. In passing through an ordinary lens, 
the component parts of a simple ray of light are variously re- 
fracted — the chemical or actinic rays of the spectrum, violet 
and invisible, being brought to a focus at a point nearer to the 
