PHOTOGRAPHIC CAMERA.

WE have now to consider the arrangement of apparatus necessary to enable us to expose the prepared plate to the action of light. For this purpose we require a dark chamber, a camera obscura, as it is commonly called.

This contrivance in its most simple form is nothing more than a box, into the middle of one end of which an opening is made to insert a lens, whilst the other end is open, and furnished with a groove, into which a dark frame containing the prepared plate is placed to receive the impression of outward objects refracted by the lens. So long as the parts work true, and the main box is constructed square and light-tight, it matters not if the outside is rough and unpolished. It would serve the purpose intended as well as if made of the most costly workmanship.

Before photography appropriated the camera to its own use, it was a mere toy; a simple arrangement to produce an image of outward objects, which one gazed upon, regretting that the power was wanting to fix and retain the delicate and faithfully coloured impression presented to the eye.

The regret then expressed cannot now be entertained; for although the pictures we now produce are defective, and wanting in colour, still they are beautiful impressions of natural scenery, and other objects.

The camera, in fact, has now become a valuable scientific instrument, hardly to be recognised under its new form and complicated arrangements, for much thought and labour have been expended in endeavouring to bring it to perfection. It has assumed many forms, and been modified in its various parts to suit the views of the operator, and to work the process proposed to be carried on by its aid.

The most simple kind of camera now in use is that made upon the French pattern; and for photography, as it is usually worked, no better form is required. It is a box with a double body, the back division of which slides out from the main body ; the bottom of the latter is prolonged backward, forming a support for the sliding division, which latter is fixed, when required, to the bottom, by means of a thumb-screw running in a slot. It is furnished with a dark frame and a focussing glass, both of which slide into a vertical groove at the back, when the plate or paper is to be exposed to light, or the focus obtained.

The dark frame of this camera should, when used for prepared collodion plates, be furnished at the bottom with a moveable glass ledge, formed of two pieces of glass, one wider than the other, cemented together, thus forming a ledge of one-eighth of an inch deep, on and against which the prepared glass plate rests during exposure in the camera. This glass ledge should, each time a picture is made, be removed and cleaned, in order that moisture and dirt may be got rid of; also a slip of glass should be cemented along the top of the dark frame, for the upper part of the prepared plate to rest against. The glass used in this dark frame should be cut a little less in width than the frame it is intended to go into; one-sixteenth of an inch less on each side.

These precautions ensure cleanliness, and prevent stains on the plate, from contact with the sides, which often arise after the dark frame has been in use a short time. The form and general arrangement of the ordinary French camera are so well known that I need not enter into a detailed account of its construction. I may, however, remark, that care should be token to ascertain that the image on the focussing glass, and that thrown upon the prepared plate, are, by a proper adjustment of the thickness of the grooves of the two frames, exactly in the same plane.

This form of camera is all that can be desired when a darkened room or a tent is at hand to excite and develope the plate in. When, however, quite away in the country, a tent is a necessary part of this apparatus. Of course, I am speaking of the use of iodized collodion, with which the whole of the manipulation has to be gone through, from the coating of the plate to the fixing of the developed image. For paper the tent is not necessary, as each sheet is merely set up in its frame in the camera, opposite the refracted image of the lens, and no further manipulation is carried on.

It has been my aim for many years to endeavour to overcome the difficulties attending the use of highly sensitive surfaces, far away from any shelter or darkened room other than that afforded by the camera itself. How far I have succeeded in this object I must leave those to judge who have tried, and are consequently able to appreciate the arrangement of camera constructed for the purpose. The camera I shall presently describe has advantages even when the sensitive paper has merely to be exposed to light, for you can, by a slight examination of the sheet previous to putting it back after exposure, tell whether the exposure to light has been too long or too short, by its exhibiting a slight change of colour, or not, over the brightest parts of the image.

Whether the camera is constructed for portability or otherwise, the contrivances for working the collodion plate within the camera will be the same; consequently, in describing one form, the same description will be applicable to all. I shall proceed to describe the folding camera I now construct. It has many advantages and improvements over the old forms, and is more capable of containing within, when folded up, the baths, chemicals, &c, which are required. It, in fact, forms a better packing-case, as well as a better camera.

The camera itself, as well as everything contained within it, is constructed as light as is at all consistent with a due regard to strength ; and it must be remembered, that a very light camera is a very useless article; the slightest wind will be apt to give it a tremor. It should have a certain weight relative to a certain outward bulk, to insure anything like stability before a wind. Although for the actual purpose of making pictures, it matters not whether the camera is constructed to fold up, or close in any way; still, for convenience in travelling, and where there is a desire, and it may be almost a necessity, that the apparatus should not occupy more space than is absolutely necessary, it becomes a matter of some importance to make the apparatus as compact as it is possible, consistent with a due regard to efficient working qualities.

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