Pentax ZX-5 ZX-5 Manual - Page 76
Snollvii3do, 030nvaov
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Calculating the flash effective distance according to the camera-to-subject distance. Guide Number (11) f /2.8 = 3.9m 3.9 ± 5 = 0.8m Maximum flash distance = Guide Number 4 Selected Thus, the flash effective distance is from approx. 0.8m aperture to 3.9m. Minimum flash distance = Maximum flash distance 5* Calculating the aperture according to the camera-to- subject distance When the distance to the subject is less than 0.7m a (2.3ft), the flash cannot be used. If the flash is used Aperture = Guide Number ± Camera-to-subject dis- within that distance, it causes vignetting in the picture tance corners, light is distributed unevenly and the picture may be overexposed. If the calculated aperture value is different than an indi- cated f-stop on the aperture ring, for instance f/3, • The value 5 used in the formula above was obtained choose the next smallest aperture ring (f2.8 in this from the built-in flash. case). SNOLLVII3dO 030NVAOV The guide number (GN) depends upon the film speed used as shown below. ISO25 -> GN5.5 ISO200 -,. GN15.6 ISO50 - GN7.8 ISO400 - GN22 ISO100 - GNI I Calculating the camera-to-subject distance in the Shutter-Priority AE Mode. The camera-to-subject distance can be calculated using the above mentioned formula. However, in the ShutterPriority AE Mode, the-camera-to-subject distance will change depending on what aperture is set. If anIS0100 film is used at an aperture of f2.8, the flash effective distance is obtained as follows: