Some time ago, curious, but not a hundred and some odd dollar curious, about how the BulzEye Pro folks had come up with the proper lens design for their products, while working on another project, I positioned a positive diopter lens, that was part of a closeup lens set that a friend had lent me, so that it was just behind the ocular of an unmounted scope, and looked through the combination, at the house across the street. What I saw, answered my question. The whole circle of the field of view was magnified, including the reticule, which was at that point out of focus. (It had not been before.) At that point, I measured the OD of the threads of the eyepiece lens cap of one of my 36X B&L scopes, which turned out to be 36mm. Then I looked to see what sizes closeup lenses were commonly found in, discovered that the list included 37mm, and found a set of new old stock closeup lenses that had probably been originally made for 35mm cameras, on Ebay, for about $20. Figuring that this was one of those experiments that I could afford to take a risk on. I ordered the set. The threads worked on my scope, at least after a fashion, and later I found that they worked on at least one of a friend's March scopes, a variable I think, perhaps the 10-60. In any case, as has been mentioned. Starting with the +1 lens I found that I had to screw the eyepiece in quite a bit to refocus on the cross hairs, and lost some eye relief as well. Because my normal eyepiece adjustment is forward of center, no doubt due to my nearsigntedness, I was limited to the +2 diopter which resulted in a loss of eye relief of about a half inch, and perhaps a 20% increase in magnification (obviously a guess). Since then I have equipped my other B&L with an identical lens, and friends have made adapters from flip open lens caps to mount them on Leupold 36s, that they continue to use that way. The original experiment that led to this was a success. I found a very hard to find, larger diameter close up lens (+ 1/4 diopter) that (when mounted with painters tape, in front of the objective) allows me to focus my scopes, parallax free, at about 12 1/2 feet, so that I can do some of the mounting chores in my garage that used to require a trip to the range, because of the close proximity of our neighbors, and not wanting to scare anyone by being seen sighting a rifle across or down the street.
