Optics:
The optical components exist of a transmission grating, a lens and the CCD.  
To use the total size of the CCD (24mm) we focus the blazed 1st order maximum of the longest wavelength onto the outer pixel. The field of view of the lens is calculated as follows:

FORMULA 1

Where  denotes the wavelength of the light,  the angle of incidence which is equivalent to the half field of view.  is the angle between the outcoming ray and the optical axis. n is the number of notches per millimeter on the grating. 
According to this the field of view has to be larger than the effective field of view. 

We found that for our purpose a field of view of XXX° is sufficient. This and the 24 mm size of the CCD allows us to determine the properties of the lens. The focal length is determined by using a simple geometric model: because of the fact that we have the same medium on the left and on the right side of the lens, the nodal and principle points fall together. A ray that travels through the first principle point remains its angle and leaves the optical axis at the second principle point under the same angle. The distance between the second principle point and the focal plane is the focal length f. Therefore one can obtain the focal length using the boundary conditions of field of view and CCD size d.

FORMULA 2

For the given conditions we obtain a focal length of XXX mm using a XXX slits per mm grating. 
Since we are working under extremely low light level conditions a low f# of the lens is essential for maximum optical throughput. An f# between 1.0 and 2.0 is suggested.

Lens, grating and CCD that satisfy these conditions are readily commercially available.