Here is the full frame of the TV-Heligon 50/0.75 on the Z/FX Nikons. The image circle projected is approx. 24mm. The similar Oude Delft 50/0.75 Rayxar projects a slightly larger circle, around 26mm diam., and as its field is slightly flatter probably will be the alternative for future use. That is, when I get my second adapter X-Ray/Z completed.