Vignetting test - a lesson learned

Concerned as to the vignetting in the last series of photos I decided to look closely at the camera and found to my horror that the opening made in front of the filter whilst the same size as that in front of the pin hole was not allowing the edge of the paper negative to "see the light".  A little bit of work with a file to make a cone shaped opening and below is the result.

 

This was a 2 hour exposure. There is not a hint of vignetting that I can see. The lack of contrast in the greys is due to the fact that I removed the yellow filter else the exposure would have been 4 hours !!! 

So in the last batch of photos it was mechanical vignetting which occurs when light beams from the object points which are located off the central axis are partially blocked by external objects in this case you could say an "improper lens hood". So nothing to do with the distance between paper negative and pinhole or anything else I might have thought that could cause the vignetting.