I expect the other tubes are flocked, and I can see a rough edge on the vignette consistent with flocking.Ultima_Gaina wrote:The 10mm segment has no flocking and the same diameter as the other tubes. I remember having tried the FF camera before (with the 10mm segment included) and there was no vignetting.
It is the absence of flocking on the 10mm tube, leaving a larger clear diameter, that makes the vignette go away. The extra extension does give some more magnification, but if the extension were flocked also, giving a smaller clear diameter, the vignette would still be there.
If I had this problem and I wanted to work at large NA where the extra extension could be problematic, then I would remove a 10 mm strip of flocking around the end of the 50mm tube, and omit the extra extension.