If we take the circle of confusion as 30 micron, the near and far limits of acceptable sharpness will be 0.42m and 0.61m, respectively. Therefore, an object at 0.4m is out of the "depth-of-field" at f/8. In order to achieve acceptable sharpness at 0.4m, you need to stop down to f/11. At this aperture, the depth-of-field is within 0.4m and 0.67m.
This calculation is based on a 25mm lens. Sometimes the nominal focal length and the actual focal length of a lens can differ quite a bit. As we all know, the Contax 25mm Distagon has a focal length of 25.9mm. I would have called it 26mm, but Zeiss decided to round it down to 25mm. The current information from the Zeiss Ikon web site has the nominal focal length only, so the calculation here might be a tiny bit off. However, in any case 0.4m is out of the depth-of-field at f/8 when the lens is set at its minimum focusing distance of 0.5m. A 22mm lens at f/8 would cover 0.4m to 0.66m, but I doubt Zeiss will sell it as 25mm.
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