Here are two photos of an inexpensive lens I bought. I have a project of sorts I would like to try using something old and "unsharp." I have figured that it focuses at infinity at about 5.5 inches. So do I measure the lens diameter to determine f stop? And seeing that the shutter is in front of the lens, do I measure the rear element? Also, the f-stops are notated as 1, 2, 3, and 4. If I can get the opening figured out, would each f-stop be one stop down? Any help is appreciated. Jim
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