I have a small 'pillbox' type lens with a doublet and front mounted washer stops. Its performance is much better close up, and even down to 1:1 than it is at infinity. I believe this is probably as a result of the fixed position of the washer stop. Am I correct in thinking that the washer stop has a specific optimum position relative to the lens itself? Does this actaully vary depending on the focused distance? Is there any useful formula which will help to position the washer stop at any given focus distance? Any other comments?
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