Though it does make sense that there would be a crop and aperture issue when using MF lenses on the 5DII, I have not noticed any issues in the slightest. See my examples below:

This one is shot with the Mamiya 80mm at f2.8, shutter speed 120, and ISO 100-
http://www.rpmproductions.info/pics/mamyia_80mm.jpg

This one with the 50mm Canon from the same exact location at f2.8, shutter 120, and ISO 100-
http://www.rpmproductions.info/pics/canon_50mm.jpg

and this one was shot closer to the subject to the subject to compensate for focal distance. It was shot at f2.8, shutter 120, and ISO 100-
http://www.rpmproductions.info/pics/...0mm_closer.jpg

From what I can tell there doesn't appear to be a crop factor or a relating effect on aperture. Maybe someone that is more experienced than I with dslrs can see something that I am not.

The "crop factor" does not change physical properties of a lens. All 50mm f/2.8 lenses will have the same angle of view a Four Thirds camera, no matter what system they were made for: Four Thirds, APS-C, 35mm, or Medium Format. For example, these all have the same exact angle of view, depth of field, and diffraction:

• Olympus 50mm f/2.8 on a Four Thirds Camera
• Canon EF-S 50mm f/2.8 on a Four Thirds Camera
• Canon EF 50mm f/2.8 on a Four Thirds Camera
• Mamiya 50mm f/2.8 on a Four Thirds Camera

Even if the lens was made for Medium Format (e.g. 645), when you put it on a smaller format (e.g. Four Thirds), the focal length and f-number do not change.

So even though a lens does not change when it used on different formats, the resulting picture does. And it helps to understand when the resulting picture is equivalent. That is where crop factor comes in.

[QUOTE=Ryan Mueller;1277645]The 150mm is minimal while the 80mm is pretty moderate. QUOTE]

Many thanks. Both seem to have significant breathing issues. The search continues.