Aperture Control With Reversed Tamron (& Other) Lenses

[Harold Gough]

This arises for a discussion in the FM Macro World forum.

Someone wanted to use a Tamron Adaptall-2 17mm prime lens reversed. I knew that, with my Olympus OM or Canon FD adapters, I could not hold the selected aperture on a reversed Tamron lens.

A few years ago I obtained a Nikon N/AI adapter, attached to a second-hand 200-500mm lens, and yesterday, by coincidence, a Pentax K adapter arrived, attached to a 350mm f5.6 mirror lens. I checked and, as suggested by the poster of the FM topic for the Nikon, both maintain the selected aperture on the lens when detached from the camera. The same will apply to fixed-adapter copies on any Tamron or other make of lens.

I have come across this difference in hold-open vs hold-close of different camera systems in this forum but a quick search did not find it.

Harold