So I took the lens off my Sony A6000 and replaced it with some tin-foil taped to the camera body. I then got the finest needle I could find and pierced the foil in the centre. Then I altered the settings to allow photos to be taken without a recognised lens being attached.
The first pictures were disappointing:
Very wide angle and very blurry (note have also used a sepia tone filter).
The problem is that the hole has to be very small, particularly if pinhole is close to the sensor, as noted in this Wikipedia article, so maybe further away would be better?
Therefore I attached the Commlite adapter to increase the distance from pinhole to sensor, cut a square of fresh tinfoil (top photo) and tried again. The results were indeed better:
Still not that sharp, but I guess that's why we uses lenses!
However it was an interesting effect and experiment to try out.