View Full Version : Scope magnificaton, nearsightedness, and getting back what we have lost....I think

Boyd Allen
12-25-2012, 05:47 PM
There are a lot of us out there, nearsighted shooters, who use scopes. Corrective lenses for this condition have negative diopter numbers....which in addition to making it possible to focus on distant objects, make them appear slightly smaller. So, those of us who wear glasses to correct for nearsightedness, are actually getting slightly less scope magnification than someone whose vision does not require correction. At this point you may be thinking, so...what's your point. Hang in there. It's coming. When you stack lenses their diopters are additive. (at least that is what my reading tells me) For example, if you stack lenses of +1 diopter, and +3 diopter, the combined magnification will be the same as a +4 diopter. Now to my point. If I am nearsighted, and have a negative diopter corrective lens in my glasses frame, that I am viewing a scope's image through, and I mount a positive diopter lens to the back of the eyepiece, the magnification of the latter will tend to cancel the image reduction of the former, while maintaining the utility of the corrective lens, when not looking through the scope.

This post is intended to provoke discussion, so if you think that I am full of beans ( on this subject...we will leave the larger issue for another time) , I will certainly understand. If you do, please explain why.

12-25-2012, 09:58 PM
I know nothing about this Boyd so I'll share a totally irrelevant experience as is my wont :)

(Well, it MIGHT be relevant, I just don't know)

I too am myopic. I ordered the Bullseye Pro "booster" lens for my 36X BRD scope. I could not get the crosshairs to clear up. I then tried to booster on several other scopes including a 45X Leupold BR. I couldn't get ANY to clear up. So I called the guy I bought it from (he useta' post here on BRC, not ER Shaw like the BulZeye website....???) and he just sais "well, it's like that for some folks."

Since you seem to be researching this maybe you can explain my situation...... maybe it pertains to the subject at hand......

And then again, I may be speaking avocado in a world of apples and oranges.

Merry Christmas!


John Kielly
12-25-2012, 11:38 PM

Don't know how long ago that happened, but recently, I had to review my boosters when presbyopia buggered up the correction for myopia - went from -4 something to -3 something dioptres & I couldn't clear the crosshairs. When I viewed the Bullseye Pro website, I found that they now offer a recommendation on how much power you can handle depending on the percentage of eyepiece adjustment you use on your scope. I had to drop back from a 4x to a 3x on my Leupold, though I can still j-u-s-t about clear on my NF BR with a 3.5X.

Interestingly, since I had a plastic lens fitted to my master eye a fortnight ago, I've checked & found that the scope adjustments haven't changed for me, so it seems that the outcome of the Bullseye Pro system is dependent on how well your eyes are set up for long distance vision.


Boyd Allen
12-25-2012, 11:41 PM
What you found out was that if your normal eyepiece focus position is too near the front limit of your eyepiece's adjustment range, that you may not have enough room to bring the eyepiece into focus. http://www.bulzeyepro.com/optical-booster-faqs.php
I have no way to know if their magnification numbers correlate to identical plus diopter numbers, but I suspect that they may. I use lenses that are not from that source, that are +2 diopter, and I may not have enough focus range to use anything stronger. Their lowest "magnification" is 2.5X. Which one did you try?

Mike Bryant
12-26-2012, 08:43 AM
I bought a Leupold 45X recently and followed the instructions on Bulls Eye Pro's web site to determine the amount of diopter that I needed. Wound up ordering the 2.5X. Probably could have used a 2X which they don't make as the reticle cleared up with the ocular lens screwed in almost to the limits of the adjustment range. Haven't used the scope yet, though, as I plan to use it on a rail gun that I have ordered from Jay. Unfortunately, my rail will be made on the next run of rail guns he makes.

Mike Bryant
12-26-2012, 08:46 AM
By the way, Red Cornelison had a pair of glasses made up for near vision on his right eye and far vision on his left eye. Said he almost fell on his face a few times walking away from the line. Too many benchrest shooters aren't with us any longer.