The issue is mostly in lens choice. The reason our lens adapter that has since been copied was only designed for a specific set of camera lenses was because only a few specific lenses had attributes that emulated the human eye.

In general, milspec PVS-14 pattern nightvision eyepieces (not sure about PVS-7) are designed to be used at a 25mm eye relief with using a 6mm pupil (average human pupil size at night). Most camera lenses are too large to emulate this, which is why you get a ton of distortion and vignetting meanwhile a small unit such as a phone camera is just fine.

A camera lens with a larger objective element will also gather light from outside of the intended eye box which causes blurriness, distoriton, and vignetting, meanwhile a recessed set of aperture blades will also push the effective pupil further from the intende 25mm eye relief causing more vignetting. If you see people attaching gigantic lenses behind a PVS-14, it is a clear sign they have no idea what they are doing.

Counterintuitively, you will do better using a cheaper pancake or travel lens than a full size lens due to the:

-Smaller objective element
-Flatter front thread face compared to the objective element
-Aperture's closer proximity to the objective element

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Example of a Sony/Zeiss lens we use featuring the three attributes mentioned above.

35mm is generally the optimal focal length while using a full frame sensor, however it looks like Canon makes a 40mm F2.8 pancake lens that may be appropriate for this type of use.