The black border around the image projected by your Nebula projector is the normal pond of mirrors (POM) of a digital micromirror device (DMD), which exists in all DLP projectors. The black border is relatively small when you have not zoomed out or keystone corrected the projected image. 

However, the black border will become larger when the image projected by your Nebula is adjusted through keystone correction or reduced by the zoom out function. As in the case of a certain projection distance, the light emitted by the projector is a fixed size area, and the display pixels analyzed by SOC will project the pixels to the above display area one by one. When the picture is adjusted through keystone correction or reduced by zooming out, the only thing that is adjusted or reduced is pixels resolved by SOC but not the light emitting area of the projector. Thus, the black border will become larger.

This is a normal phenomenon but not a quality-related issue. To avoid a larger black border around the image, please:

1) Move the projector closer to the screen to get a smaller projected image instead of projecting a zoomed out image;

2) Do not use keystone correction but try to adjust the position of your Nebula to a proper angle to get a rectangular projected image.

If you have additional questions, please contact us for further assistance.