I measured angle g for multiple distances (D) between the entrance slit and the grating.
I made a few measurements on the SpectroBench 2000 of the best angle for the grating if it is made from a piece of DVD+R. I am not sure if most people are using DVD-R or DVD+R. Let me know if I should repeat these measurements with DVD-R.
With the entrance slit about 0.2 mm wide, I varied the distance (D) between the slit and the grating between 7.8 and 25.5 cm. I rotated the grating until the spectrum appeared sharpest to my unaided eye and measured the angle of the grating (g). I took measurements with the piece of DVD in two orientations: Either the outer, lower surface of the DVD was toward the slit, or the inner surface (exposed when delaminating the DVD) was toward the slit.
The result is similar to when the grating is a piece of 1000 lines/mm film, but the DVD+R grating must be rotated at a slightly steeper angle. When the slit-to-grating distance is less than 15 cm, the best angle is between 70 and 75°. There is no difference in best angle between the two orientations of the DVD. However, the curvature of the lines does seem to make a difference to the size of the spectral image. When the angled light approaches the DVD surface from the concave side of the lines the diffraction pattern is taller.
I did not measure the offset of the viewing angle from normal to the grating because I am not sure this affects the sharpness of a photographic image. But in order to center the visible spectrum in a photographic image, the camera would have to point 10° or 15° from perpendicular to the grating. If the near infrared spectrum is also being photographed, pointing the camera normal to the grating would probably work well.