THE CAMKKA.] 



UNDULATORY FORCES. LIGHT PHOTOGRAPHY. 



143 



consequently are soon discouraged by failure. Our re- 

 marks on aberration* will at once suggest to the in- 

 telligent reader, that the construction of an accurate 

 camera depends on an extended acquaintance with the 

 laws of optics, combined with a high degree of skill on 

 the part of the maker ; and of course such acquirements 

 both demand and deserve an adequate pecuniary recom- 

 pense ; hence the high price of some cameras employed 

 in the art. If a lens could be ground of such an exact 

 shape as to overcome the occurrence of spherical aber- 

 ration, as easily as the difficulty of chromatic aberration 

 has been dealt with, such would, of course, almost arrive 

 at perfection. We here observe how exact are the works 

 of the Deity compared to the best productions of human 

 skill. In the eye we have every change of circumstance 

 at once provided for,-as we have already explained when 

 treating on the eye and its structure. Now, the lens of 

 the camera has to fulfil the same object as the crys- 

 talline lens of the eye ; and to extend our analogy, we 

 may add, that the prepared plate of the photographer 

 is the analogue of the retina of the eye ; for, like it, it 

 has to receive and communicate impressions of the rays 

 of light incident on its surface. 



It would, of course, be highly improper for us to recom- 

 mend any instrument-maker, in preference to others, of 

 whom the student might purchase his camera, and other 

 photographic apparatus. We, however, shall attempt 

 to explain the advantages and improvements which have 

 been introduced by various persons ; and giving the 

 I student an opportunity of judging of the essential points 

 ! to which hU attention should be directed, we must 

 leave to his own judgment and preference, the particular 

 form, <tc. , of the instruments he may desire to obtain. 

 Two classes of cameras, or at least two sets of lenses 

 for the camera, are necessary, for the separate purposes of 

 taking likenesses and landscape views. This will be 

 ; evident when it is remembered that, in the first instance, 

 the object may be placed close to the instrument ; 

 whereas, when taking a photograph of a country scene, 

 Arc., the different objects will be at all possible distances 

 from the centre of the lens. The human eye is capable 

 of adapting itself instantaneously to the variations of 

 distance in respect to objects seen by it ; and to a 

 certain, but not entire extent, the same result is 

 effected in the position of the lenses of a camera by 

 a mechanical arrangement the operation being termed 

 " 



In the annexed engraving, the general arrangement 

 of the photographic camera is represented. In Fig. 144, 



Fig. 144. Fig. 145. 



A represents the box of the camera; B a brass 

 tube in which the lenses are placed; C a slide or 

 dark frame, in which the sensitive plate is fixed. In 

 Fig. 145, 1) shows this frame in its details; the back 

 being opened, so that its internal construction may be 

 observed. 



The image received on the ground-glass plate at C, in 

 Fig. 144, U focussed in this form of camera, by moving 

 or adjusting the lens contained in the tube B in front of 

 the camera ; hence its use will be necessarily coiitiued to 

 occasions wherein such limited adjustment is admissible 

 or required. Another form of the camera, in which the 

 distance between the ground-glass plate for viewing the 

 image, and the tube in which the lenses are placed, is 

 illustrated in the following engraving. 

 See unit, p. M. 



In Fig. 146, we observe that the box of the camera 

 Fig. uo. is divided into two 



parts, of which B is so 

 constructed as to slide 

 easily in and out of 

 A. Thus the ground- 

 glass plate represented 

 in the frame D, may 

 be extended to and 

 fro from the lens, and 

 a greater focal ar- 

 rangement can be ar- 

 rived at. 



A very convenient 

 form of camera, for travelling purposes, is represented 



Fig. 147. 



in Fig. 147. The body of the box, instead of 

 being solid, is made exactly like the bellows of the 

 concertina. The back, c, holding the plate, can thus, 

 by means of the folding construction of 6, be easily 

 shifted any distance from a, the part of the arraiige- 

 m> nt hi tiding the lenses; and all parts are maintained 

 in a firm condition, when in use, by means of the cross- 

 bars d d. These are secured in any desired position by 

 means of screws working through slots in the bars. 



We need not, however, occupy further apace by de- 

 tails of- those forma of the camera which result from the 

 peculiar choice, requirements, or means of the operator. 

 Any, or most of these, may be inspected at the optical 

 instrument-makers, who, according to their individual 

 opinions on the subject, will bo able to give more pre- 

 cise and effective descriptions than it falls to our pro- 

 vince to attempt. We may, however, offer a word of 

 advice to those who may be desirous of purchasing ail 

 instrument; and, in so doing, we need scarcely state, 

 that the purchaser will do wisely to seek his apparatus 

 at any house whose reputation for skill and respecta- 

 bility is well attested. Achromatic and properly ground 

 lenses, their transparency, firmness of workmanship in 

 the material of the box, are the essential points. We 

 have seen cameras made of unseasoned material, in 

 which some of the parts of the woodwork have con- 

 tracted by change of weather, which rendered them ex- 

 tremely inconvenient, not to say useless. In such cases, 

 the dark frame, by fitting too tightly or loosely in the 

 slide receiving it, will often cause the camera to be 

 shifted whilst introducing the 

 sensitive plate, and so entirely 

 remove the camera itself out of 

 position, and destroy the focus. 

 We can only add, " caveat emp- 

 tor." 



The camera requires a steady 

 support, and one which can be 

 adapted so that it may be placed 

 in any position. One of the 

 most convenient of these ia that 

 represented in Fig. 148 ; and 

 one. of this kind is equally avail- 

 able for house and out-of-door 

 use. Great care should bo ob- 

 served in purchasing or making 

 a stand of any shape, because the 

 use of unseasoned wood soon 



Fix 148. 



