Recall that the guider has rectangular pixels of dimension 13.75x16 microns. Given this, I adopted the strategy of obtaining pairs of guide CCD images of the double stars from Table 5 with the camera rotated such that the two stars in the double were aligned roughly parallel with the x-axis, and then with the y-axis. Figure 34 shows one such pair of guide CCD images.
I measured the pixel-locations of each component of the binary on each image, and determined their separations in x and y. I then used the known separation in arcseconds to determine a measure of the plate scale (in arcseconds per micron) for each image. The average of the ensemble gives the final measure of the plate scale for the guider. The field of view follows from the size in pixels, and the slit width in arcseconds from the known slit width in microns. Table 6 gives the resulting quantities for both optical configurations (with and without the focal reducing lens).
Mode | x-axis | y-axis | FOV | 18 micron slit | 72 micron slit |
'' per pixel | '' per pixel | '' x '' | '' | '' | |
No lens | 0.52 +/- 0.02 | 0.60 +/- 0.02 | 98 x 97 | 0.7 | 2.7 |
Lens | 0.68 +/- 0.04 | 0.80 +/- 0.05 | 130 x 129 | 0.9 | 3.6 |