Sigma 50mm f/1.4, MFA, and upgrade from 5D to 5D III

About 1-1,5 year ago or so I have read reports  that the amount of MFA needed depended on focus distance. The difference was such that no MFA setting could be found to cover an acceptable range. With a little search you may be able to find that thread.

Of course that thread was pre- 5D3, but the issue would seem to be lens related. For sure it will show in your tests if your lens has this issue.

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cheers,
Dick