I understand that the best pinhole apertures are made from as thin a material as possible usually by thinning the material at the edge of the hole in someway. The use of gold or silver foil may assist with this. I believe the pinhole which was provided in the Bulldog kit is laser cut, since there is no sign of edge relieving, although it is in very thin material supported on thick card. The pinhole being centred over a 5mm hole through the card.
It looks like it is probably 0.5mm diameter, so the “tube effect” may give the vignetting that you propose. I shall make exposures at both 125 and 250mm and compare the negatives today; light permitting.
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