Roof diopter ring adjustment

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Rogan
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Roof diopter ring adjustment

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Post by Rogan »


I have a pair of Bushnell Legend Ultra HD 10x36 roof binoculars that I greatly value. I love the Legend Ultra HD (I also have 8x36) and find a 36mm objective to be a real sweet spot. I got the 10x collimated (thanks Suddarth Optical) but found that the diopter was all the way to the plus side on the adjustment to get perfect focus balance between right and left barrels. I don’t believe that it was an issue with my eyes as I have not had this issue otherwise. While it was fine I really didn’t like having the setting all the way to the end as there was no further room for future adjustment should my eyes change. Cory Suddarth had said that it would be an easy fix. I filed that away for the future if need be. Then, this weekend, the focus wheel cover came off on a pair of Redfield Rebel 8x32. That got me to looking inside the focus wheel where I saw the ends of the two rods/plungers that move the lenses inside of the barrels to change focus. I was familiar with that mechanism but noted that the brass ends of the rods were slotted which I assumed to be for adjustment. Noting the orientation of the slot I tweaked one side and saw that the focus balance between the two barrels was altered requiring we to tweak the diopter adjustment to achieve focus balance. My thoughts immediately went to the Bushnells.

The first step with the Bushnells was to remove the focus wheel cover which easily popped off. Through the skeletonized face plate I could plainly see the two brass ends of the focus pushrods and they were slotted for adjustment. Again noting the beginning orientation I rotated the rod on the diopter adjustment side. The focus balance was clearly affected and I determined that a clockwise turn of the slot would alter the diopter adjustment back towards “0”. Next I set the diopter ring to a zero adjustment/setting and locked the ring down. I then focused so the left barrel was perfectly in focus. Next I rotated the diopter side slotted pushrod clockwise until perfect focus balance was achieved which required constant visual checks along the way. The result is that now with the diopter adjustment set in the middle on “0” there is perfect focus balance between the two barrels. The binoculars are zeroed for my eyes with equal room for adjustment either way if need be. Now that I think about it I have seen these slotted ends with other roof focuser mechanisms so I’d be confident this fix would be a common one.
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