Oldal 86 [86]
OCR
4) If working outside the studio or in the field, position the UV radiation sources and the camera around the subject accordingly. 5) Position the reference standards as recommended in section b. A scale may also be inserted in the image if reguired. 6) Puton UV safety glasses. 7) Turn on the UV radiation sources and allow them to warm up for 20 mins. 8) Turn the room lights off. 9) Ensure that both the subject and reference standards are evenly illuminated, checking with a light meter if preferred. Camera capture settings 10) Camera settings will vary according to the equipment used but some general camera settings are recommended in section b. Exposure settings 11) The exact exposure settings will vary with the equipment used but some general exposure recommendations were made in section b. 12) Particular recommendations for acquiring UV-reflected images: (a) Aperture settings in the middle of your lens range (e.g. f8) are usually a good starting point for maximum sharpness, but choose depth of field according to dimensionality of subject, as advised in section b. (b) The low sensitivity of camera sensors to UV radiation usually means the use of large apertures (low f-stop number). (c) As a result of this limited sensor sensitivity, shutter speed will generally be quite long (e.g. 1 sec). Adjust this as required for correct exposure. Obtain an image of the uniform reflective board 13) Place the uniform reflective board so that it is evenly illuminated and fills the frame of the camera. As far as possible the board should be in the same plane as the subject so that the illumination on it is representative of the illumination on the object. 14) Focus on the board. Defocus slightly. Take the image. 15) Check the image exposure. The RGB values of the image on the image histogram (Figure 2-29) in playback mode are a good indicator but note that these values pertain to the preview J PEG generated by the camera not the RAW data (see Chapter 3).*" Version No. 1.0 78 Date : 14/10/2013
