Stranica 96 [96]
OCR
4) If working outside the studio or in the field, position the visible light 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) Turn on the LED light sources. 7) Turn the room lights off. 8) Ensure that both the subject and reference standards are evenly illuminated, checking with a light meter if preferred. Camera capture settings 9) Camera settings will vary according to the equipment used but some general camera settings are recommended in section b. Exposure settings 10) The exact exposure settings will vary with the equipment used but some general exposure recommendations were made in section b. 11) Particular recommendations for acquiring visible-induced IR luminescence 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) Aperture settings will be dependent on the intensity of the luminescence emitted, which will in turn be dependent on the nature of the material being examined. For weakly emitting cases, large apertures (low f-stop number) may be required. (c) Shutter speed will generally be quite long (e.g. 1 sec) but will again be dependent on the intensity of the luminescence emitted. Adjust this as required for correct exposure. Obtain an image of the uniform reflective board 12) 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. 13) Focus on the board. Defocus slightly. Take the image. 14) Check the image exposure. The RGB values of the image on the image histogram (Figure 2-35) 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 88 Date : 14/10/2013
