Diffraction experiment not h/w question

[indie452]

I'm doing a project which involves the need to find the diffraction pattern of the sodium d lines from a sodium lamp using a telescope (focal point 3.39m) and a lens that causes the light 'rays' that hit the diffraction grating to be parallel to each other.
the diffraction grating follows the littrow condition so a=B as the input and output are along the same axis.

The diffraction grating for sodium wavelength we found the 20.37degrees for 1st order

So we have taken a ccd image of the diffraction pattern and we are getting 2 dots one above the other instead of 2 vertical lines parallel to each other

Does anyone know anything that might help us explain this?

We don't need to rotate the camera as it gave us a vertical line when we used a mirror in place of the grating to find the focal point.

 

[Gokul43201]

Could those just be the 0th order peaks you are looking at, and for some reason, related to your collimation arrangement, they are vertically separated?

 

[indie452]

not really our grating is blazed and so should give a very distinct result at 20 degrees (first order from the diffrection grating)

also the set up is as such that the lines of the grating are in the same axis as the slit