Focus shift in the 50mm Sonnar ZM at close range

[eric_cheek]

<p>I have this lens and was concerned about focus shift from net reading and some focusing difficulties. I spoke to Zeiss and they advised that the lens is averaged to minimize the problem.<br />Thereafter I conducted several tripod test at all apertures from 1.5 to f/16 using a statue at close range focusing on the eyes. At all apertures I was unable to find any focus shift even though the images were blown up to 100%. Of course, I would not expect a problem by the time I reached f/4 even if focus shift was a real issue.<br />In practice I take everything at 1.5 - as the bokeh is great and I like a narrow DOF mostly. If I want a slower shutter speed I use an ND filter rather than stopping down to f/2-f/4. Not perfect - but OK.<br />I think the focus shift is a non-issue in practice and apprehend that the problem is more likely camera movement and/or inaccurate focusing. My difficulties were that my M9 has a built in diopter measurement of -5 but I need +1.5. Buying a +2 diopter solved the issue.<br />If anyone is concerned Zeiss will optimize this lens (free of charge in warranty period) to ensure accuracy at 1.5. or or presumably other apertures but this will cause more of a problem where other apertures than that to which the lens has been optimized are used.</p>

[eric_cheek]

<p>I have this lens and was concerned about focus shift from net reading and some focusing difficulties. I spoke to Zeiss and they advised that the lens is averaged to minimize the problem.<br />Thereafter I conducted several tripod test at all apertures from 1.5 to f/16 using a statue at close range focusing on the eyes. At all apertures I was unable to find any focus shift even though the images were blown up to 100%. Of course, I would not expect a problem by the time I reached f/4 even if focus shift was a real issue.<br />In practice I take everything at 1.5 - as the bokeh is great and I like a narrow DOF mostly. If I want a slower shutter speed I use an ND filter rather than stopping down to f/2-f/4. Not perfect - but OK.<br />I think the focus shift is a non-issue in practice and apprehend that the problem is more likely camera movement and/or inaccurate focusing. My difficulties were that my M9 has a built in diopter measurement of -5 but I need +1.5. Buying a +2 diopter solved the issue.<br />If anyone is concerned Zeiss will optimize this lens (free of charge in warranty period) to ensure accuracy at 1.5. or or presumably other apertures but this will cause more of a problem where other apertures than that to which the lens has been optimized are used.</p>