Of course there is no absolute state of “sharpest focus,” but when we use the word “sharp” we mean the sharpest focus obtainable by any existing photographic lens when used in the ordinary way.
CHAPTER VI.
EXPOSURE.
Ways of exposing.
A plate can be exposed in three ways, that is, by removing the cap and replacing it, when the exposure is made; by folding the camera cloth and placing it over the lens (the cap having been removed), before the shutter of the dark-side is drawn, and then quickly withdrawing and replacing the cloth and sliding back the shutter; and thirdly by using a mechanical aid, called a shutter.
The first method needs no comment save that the cap should be withdrawn in an upward direction. The second method has been of invaluable service to us, and is much practised by Scotch photographers. By this means very rapid exposures can be made, and yet detail obtained in dark foreground masses. |“Instantaneous shutters.”| The third method is so well known that hundreds of mechanical contrivances, called “instantaneous shutters,” have been invented. |Quick exposures.| We have always done all the work we could by quick exposures, and here we may at once say that for artistic purposes “quick exposures” are absolutely necessary where possible. |“Instantaneous.”| We do not say “instantaneous exposures,” because it is high time that this unmeaning word should be relegated to the limbo of photographic archaics. Is it not obviously illogical to call exposures of 1/200 of a second, and of one second, both instantaneous?—yet such at present is the custom. “Instantaneous” means nothing at all, for a quicker exposure can be obtained by the second method we have described than with some shutters. |Classification of exposures.| It is in fact difficult to classify exposures, for obviously the classification must be based, cæteris paribus, on the time the plate is exposed, and this, especially in quick exposures, is not to be measured save by special apparatus, which of course is of no rough working use. We offer as a suggestion the following rough working classification for describing exposures. We would define as
QUICK EXPOSURES,
Quick exposures.
Uncapping and capping lens as quickly as possible. Snatching velvet-cloth away and replacing it as quickly as possible. All shutter exposures which cannot be timed by the ordinary second-hand of a watch; a note being added in the case of shutter exposures, giving make of shutter, and stating whether it was set to quickest, medium, or slow pace.
TIME EXPOSURES.
Time exposures.