A handbook of photography in colours / Thomas Bolas, Alexander A. K. Tallent, Edgar Senior.

  • Bolas, Thomas.
Date:
1900
Catalogue details

Licence: In copyright

Credit: A handbook of photography in colours / Thomas Bolas, Alexander A. K. Tallent, Edgar Senior. Source: Wellcome Collection.

    148/458 (page 126)
    The length of spectrum obtainable from red to > violet (visible in daylight) will be dependent on several factors. ist. The dispersive power of the prism. 2nd. The angle of the prism. 3rd. The angle which the incident rays make with the first surface. 4th. The focal length of the telescope or camera lens. 5th. The inclination of the surface on which the rays are focussed to the axis of the camera lens. The dispersive power of the prism. If the angle between the red and violet rays (visible by daylight) is known, then the length of spectrum can be calculated for a certain focal length of the camera lens. Fig. 18. Focal length and size of image. The diagram (Fig. 18) will illustrate this, suppose the angle 30 and the camera lens 2ft. focus, then mul- tiplying the focal length in inches by ’0524 will gb e the length of spectrum in inches (at right angles to the axis of lens) 24 X -0524 = 1-2576 or i£ inches. For a six feet lens 72 x -0524 = 3-7728 or 3f inches.