E. Emerson on Improvements in the Photographic Camera. 281 
Portrait combination, 6 inches focus. Pin-hole alone. 
1. One second exposure, one inch 1. One second exposure,—result 
diaphragm, a good negative, nothing. 
2. Thirty seconds exposure, half 2. Thirty seconds exposure, result 
inch diaphragm, a good negative. almost nothing. 
3. One minute exposure, { inch 3. One minute exposure,— faint 
diaphragm, good sharp negative. shadowy outline of a picture. 
4. Two minutes exposure, 74 inch 4,. Two minutes exposure, middling 
diaphragm, excellent negative, contrast between light and shade 
details of objects witha mile good but exceedingly blurred in all the 
under a magnifying power of 100 etails. 
diameters, : 
5. Three minutes exposure; picture 5. Three minutes exposure, view of 
over-exposed, with +4; inch dia- a white bust in thesun-light, good 
phragm. contrast of light and shade, pic- 
ture only of the prominent outlines 
looked like a very rough mosaie. 
6. Three minutes exposure, 74; inch 6. Seven minutes exposure, negative 
diaphragm, good negative, but strong enough to print from ; but 
“not sharp enough for a power of no sharpness at all; details blur- 
50 diameters. red and confused. 
, The results of these experiments may be summed up as fol- 
ows :— 
1. It is found in practice that a quartz lens is quicker in action 
than a common glass lens of the same aperture, focus and thick- 
ness, 
2. A i lightly quicker than the double 
uartz lens is very slightly qui Sn antag any 
thing like so sharp details even under the smallest diaphragms. 
“ 
the picture, and requires from three to seven minutes Vik gina 
with the most sensitive collodion. This lack of sharpness might 
have been predicted theoretically. To give sharpness e 
rays of licht from a single point travelling such paths as are 
indicated i the diaertor’ phodoe necessarily a blurred image; 
thus—(fig. 2,) i. e., sharpness will be 2. 
Mm proportion to the smallness of the 
Pin-hole; now as a pin-hole of the 
with the most sensitive collodion an 
€xposure of several minutes, 1t 1S 
Sandth of an inch in diameter would : elled, 
Tequire an exposure entirely impracticable. We are comp 
