Olympus OM to Minolta SR adapter ring

Question

Is there an adapter ring available to mount Olympus OM lenses to a Minolta SR mount?

Specifically, I'm looking to swap a lens between my OM10 and Minolta X-700.

Answer 1

Is there an adapter ring available to mount Minolta SR lenses to an Olympus OM mount?

The registration distance, sometimes called the flange focal distance, of the Olympus OM mount is 46.00 mm with a throat diameter of 46mm. The registration distance of the Minolta SR mount is 43.5mm with a throat diameter of 44.97mm.

To adapt an Olympus OM lens to a Minolta SR camera, the lens flange needs to be held 2.5mm in front of the camera's flange ring. The big issue here is that the OM lens' deep flange lugs extend 4.5mm behind the the flange contact surface. Since the throat diameter of the OM mount is 46mm and the throat diameter of your SR camera is only 44.97mm, the lugs on the 46mm flange ring of the Olympus lens will not be able to fit through the smaller 44.97mm flange ring of the SR camera. So it is physically impossible to adapt an OM lens to an SR camera without additional optics.

To adapt a Minolta SR lens to an Olympus OM camera the lens flange on the lens would need to protrude 2.5mm inside the camera in order to be able to focus at infinity. The Olympus camera has a throat diameter (the diameter of the hole in the middle of the flange ring) of 46mm. The throat diameter of the SR mount is 44.97mm. The difference of only 1.03mm is not enough to accommodate the bayonet lugs of the SR lens inside an adapter ring and allow the adapter ring to fit into the throat of the Olympus camera. So it is physically impossible to adapt an SR lens to an OM camera without additional optics.

Additional optics have several disadvantages that normally make them not worth considering:

• They reduce the angle of view of the lens when adapting a lens with a shorter registration distance to a camera with a longer one. The magnification needed to allow infinity focus means the focal length of the lens+adapter is longer than the lens without the adapter.
• The magnification also reduces the lens' maximum aperture number, since the f-number is the focal length divided by the entrance pupil diameter. If you increase the focal length with additional magnification but don't increase the size of the entrance pupil, you reduce the f-number. Even 1.4X magnification results in a full one-stop reduction in maximum f-number.
• Cheap adapters tend to have cheap optics that degrade image quality significantly. Producing an adapter with good optics very often would cost more than the lens one wishes to adapt.
• High quality magnifiers placed between a lens and the camera are often called teleconverters or extenders. Good ones cost around $500 or more. Even those are only really effective with the longer focal length lenses for which they are created to be used. When used with shorter focal length lenses, the decrease in image quality is usually too great to make them useful.

For a fuller examination of all of the issues with adapting lenses in one mount to cameras with another mount, please see: Can I use lens brand X on interchangeable lens camera brand Y?