Last Friday, I received the step-down ring I ordered (bought here
) to test the GT1 lens with GRDIII. It's made from metal, and looks well finished and durable.
The result is exactly what I expected it will be. There is some vignetting and it looks worse in JPEG than in DNG. I think its just the additional contrast and other JPEG processing that makes it worse. Another problem is, that the step-down ring I got is too thick (the thickness of outer part is 4mm, total thickness of ring is 6.5mm). I think it's a problem of most of step-down rings? There are some thinner rings, but they are hard to find. What we need is really thin ring that reduces the vignetting to it's bare minimum. The problem is, that there may be a problem with durability of too thin ring.
In any case, the vignetting with step-down ring is much noticeable in 4:3 and 3:2 and it's almost invisible in 1:1. Next time I will try also the sharpness
Here you can see how the GT1 vignetting looks in various aspect ratios:
Two real-world examples:full resolution filefull resolution file