Tecnai on-line help manual -- Options - UT Southwestern

<strong>Tecnai</strong> on-line help Options 105Options Software version 2Camera constantThe magnification of the stereographic projection and the other elements displayed depends on thecamera constant. This value can either be defined by hand, using the camera constant slider, orautomatic (in which case it is linked to the active camera length). The range of camera constants usedby k-Space Control is 1 to 20.The camera constant (the camera length*the electron wavelength) is in mm*nm, so a camera constant of1 means a distance of 1 mm corresponds to 1 nm d spacing (on the printed page; due to monitor sizedifference these values may not be exact on the monitor display).The camera constant (L*λ) forms part of the formula for converting distances in a diffraction pattern to dspacings:D*d = L*λ or d = (L*λ ) / Dwhere D is the distance of the diffraction spot in the pattern to the origin of the pattern (the transmittedbeam). Thus while 1 mm at a camera constant of 1 means 1 nm d spacing, 2 mm means 0.5 nm dspacing (as D occurs in the denominator).Table of (approximate) camera lengths against camera constant for different accelerating voltages.Cam. const. 120 kV 200 kV 300 kV1 300 mm 400 mm 500 mm5 1500 mm 2000 mm 2500 mm10 3000 mm 4000 mm 5000 mm20 6000 mm 8000 mm 10 000 mmNote: For displaying the diffraction pattern, it is necessary to choose a larger camera constant,otherwise the spots will be too close together and invisible. If the diffraction pattern display is on and nopattern is visible, increase the camera constant.The display at the smallest cameraconstant.