Stacking mamiya 645 35mm with 80mm macro: Fail!!!

austrokiwi1 · Post by **austrokiwi1** » Tue Mar 24, 2015 5:41 am

In my collection of lenses I have two Mamiya medium format(645) lenses; a Sekor C 80 mm macro( not "N") and a 35mm F3.5 N. I thought I would try stacking them. Reversing the 35mm and mounting it on the 80mm in theory gives a magnification of 2.28. I obtained at minimal price the requisite coupling ring...... set it all up took one look in the camera's LCD screen and disassembled it all. It did look as if I gained the theoretical magnification but the image circle was tiny on the full frame sensor. The image looked very much like that I would anticipate if I had mounted a MFT lens on my FF camera. My FF 7.5 mm fish eye produces a larger image circle than what I saw today!

So for those of you who have lain awake wondering whether you should go out and stack a 35mm Medium Format lens on an 80mm Medium format lens and then mount it all on a 35mm camera.....you can now sleep easy....It doesn't work!!!!

rjlittlefield · Post by **rjlittlefield** » Tue Mar 24, 2015 8:14 am

This sort of vignetting is always made worse when both lenses are stopped down. Did you for sure have the rear lens wide open when you made your test?

--Rik

austrokiwi1 · Post by **austrokiwi1** » Tue Mar 24, 2015 8:50 am

I was pretty sure I had tried both lenses wide open. But as a check I went back and tried again with both wide open. I then switched the camera to APSc capture mode....there was still vignetting but it almost filled the APSc sensor area. The 35mm lens is a wide angle it has a very small exit pupil is that the problem? Heres what the stacked lenses produce in APSc mode. The photo is pretty bad as it was taken hand held

rjlittlefield · Post by **rjlittlefield** » Tue Mar 24, 2015 10:57 am

This sort of vignetting is caused by a mismatch between the exit pupil of the front lens and the entrance pupil of the second lens. Light rays from the edges of the field get through the front lens OK, but by the time they get to the aperture plane of the rear lens they're too far off center to get through the hole. That's why closing the rear aperture makes the problem worse.

So, the problem is not so much that the 35's pupil is small, but that it's far in front of the 80's pupil.

--Rik