I have an application where I need as large a physical aperture as possible. By physical, I mean actual aperture in mm, not as an f-number. I also need this lens to focus to about 0.5m. I have the 85mm Nikkor f/1.4, which has a diameter of about 60mm, but doesn't focus close enough for me. Sigma have a 180mm f/2.8 macro which should be about 64mm diameter. Is there anything commercially available that is larger?
Since people in the comments have requested why I'd like to have a large diameter, I have added this diagram to explain what I am trying to do. My goal is to maximize the angle, theta, which represents the proportion of scattered light that reaches my lens. For a fixed focal distance, that means maximizing the diameter of my lens.
Answer
The 180mm F/2.8 EX DG OS HSM APO Macro has in fact the largest diameter among lenses which focus at 50cm or less. 64mm as you suggested.
This search was done internally on my database at Neocamera which includes all consumer lenses currently available, so over 1200 lenses. To find other options you may have to look at lenses for large format film cameras.
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