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Focus beyond infinity

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#1 Jon Isaacs

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Posted 06 January 2013 - 10:10 AM

A friend and I were comparing binoculars last night and I discovered that he is very near sighted, 8 diopters in one eye, 8.4 in the other. Apparenty though he has very little astigmatism so he would like to try observing without his glasses.

We were comparing three 10x50s, the NIKON Actions, the NIKON Action Extremes and a pair of Celestron Regal Roofs. There was insufficient focus beyond infinity for him to reach focus with either of the Nikons, he could reach focus with the Regals but only at the very limit.

Is there a specification for focus beyond infinity or any recommendations of particular models that are good in this regard?

Best wishes... Clear skies ahead. :jump:

Jon

#2 BillC

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Posted 06 January 2013 - 10:44 AM

Recess the objectives; a little dab'll do ya.

BillC

#3 Brent

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Posted 06 January 2013 - 10:53 AM

Hi Jon,

I don't have any recommendations of any particular models, nor do I know what specs are used by various manufacturers. However, I thought it might be worth sharing the following information. I too am nearsighted (though not severely so), and several years ago I purchased a new pair of Trinovid 10X50 BNs, through which I could just reach infinity focus without glasses. I called Leica and asked if the focus beyond infinity could be extended (since I wasn't expecting to get less near sighted as I age), and they said "no problem," and gave me a few more diopters free of charge.

Again, I don't know what the limits are regarding how far beyond infinity focus any given brand may be adjusted. But whether such adjustment is possible for a given brand might be worth checking into. I realize that's not what you were asking for, but I offer it in hopes it might be of some help to your friend.

best,

Brent

#4 Rich V.

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Posted 06 January 2013 - 10:55 AM

Usually the best bet for nearsighted users are IF binoculars; they give equal +/- diopter correction.

CF binos seem to push this +/- balance into the + side to attain better close focus capabilities.

The problem for your friend is that even most IF binos are approaching their limit at +/- 8 diopters. I'm just the opposite of your friend; I'm +8 diopters farsighted. My Fujinon IF binos didn't give enough range (about +/- 7d) for me so I had Cory Suddarth extend the + range of the eyepieces a bit at the sacrifice of the -. My WO 22x70s (KUO BA8 platform), however, give me just enough diopter range to focus for me without my corrective lenses. Perhaps other sizes in this binocular line have a similar diopter adjustment range.

I suggest your friend try several IF 10x50s; perhaps he'll get lucky and find one that just reaches the focus he requires. The modification option like I had done is always there.

I don't recall seeing any tabulation that shows what specific models of binos have the most in-focus range for nearsighted users. Perhaps EdZ has some notes he's made, though. He, if anyone, would have noted this kind of info.

Good luck,

Rich






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