The spectral format shown below is imaged onto a 4k x 4k CCD with 15 micron pixels which allows continuous wavelength coverage from 350 nm to 1000 nm. The minimum physical separation between orders is 0.4 mm. At the highest resolving power (R ≈ 60K) there is at least two pixels of clear background on the CCD between the object and sky spectra. Order 35, 969.23 – 997.32 nm is forced to fit across 4088 pixels, thereby allowing 4 spare pixels at each edge. So the short dimension (4096 pixels) be in the direction of high dispersion.
The non-linearity of the cross-dispersing prisms’ dispersion and the lateral colour in the camera combine to place the most closely spaced echelle orders in the vicinity of order 43. This is shown in figure and it can be seen that at least two clear pixels separate the closest orders in high-resolution mode.
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