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 Post subject: Eyeglass lens
PostPosted: Thu Sep 14, 2017 10:12 am 
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Joined: Fri Aug 28, 2009 8:46 pm
Posts: 4
How should eyeglass lens be ground for ten meter air pistol shooting? Should they just be regular prescription, ground to focus on the front sight, or something else?


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 Post subject: Re: Eyeglass lens
PostPosted: Thu Sep 14, 2017 10:21 am 
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Joined: Mon Mar 01, 2004 12:31 pm
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Location: New Hampshire, USA
Please, let's not reinvent the wheel. There are dozens, maybe hundreds of posts here on this very subject to say nothing of the literature by optical expert Dr. Norman Wong and a very readable article by the late (and greatly missed) competitive pistol guru Don Nygord.


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 Post subject: Re: Eyeglass lens
PostPosted: Thu Sep 14, 2017 10:37 am 
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Joined: Sat Nov 15, 2008 4:20 pm
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Location: Scottsdale AZ
Yes.


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 Post subject: Re: Eyeglass lens
PostPosted: Thu Sep 14, 2017 11:07 am 
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Joined: Fri Aug 28, 2009 8:46 pm
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Where are the articles?


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 Post subject: Re: Eyeglass lens
PostPosted: Thu Sep 14, 2017 11:37 am 
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Joined: Mon Mar 01, 2004 12:31 pm
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Location: New Hampshire, USA
Plenty of information if you use the SEARCH function - above and to the right. There is also a thing called "The Google."


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 Post subject: Re: Eyeglass lens
PostPosted: Thu Sep 14, 2017 12:13 pm 
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Joined: Mon Mar 01, 2004 12:49 pm
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Location: Ruislip, UK
If you're under 40 you might get away with your normal distance prescription with a +0.5 dioptre adjustment.
For most people a +0.75 dioptre adjustment will be right.

If your normal distance prescription is quite strong, e.g. -6.0 dioptre or stronger, the distance between the eye and the lens becomes more important. As shooting frames frequently hold the lens further away from the eye than normal frames you would probably be well advised to take your shooting frames and gun (with permission) to a good shooting optometrist and get your eyes tested properly.


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 Post subject: Re: Eyeglass lens
PostPosted: Thu Sep 14, 2017 10:54 pm 
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Joined: Fri May 18, 2012 9:37 pm
Posts: 250
Location: Cincinnati, OH
The math is very straight forward, and the answer is distance +0.75 diopters for almost all shooters. If you have exceptionally short arms it might change to a +1.00, but that is rare.

I'm an engineer who studied optics, not an eye doctor, so I come at this from the perspective of deriving the solution based on theory and math, rather than the eye doctors who often either try the "A or B" approach, or else just assume they know the answer, when indeed they don't understand the problem.

THe actual optical solution is that youwant to center your eye's depth of field between the rear sight and the target, providing equal focus on the two, with slightly improved focus on the front sight. To do this, you want your eye relaxed focus to fall at the rear sight hyperfocal distance, which is twice the distance from your eye to the rear sight. eg, for my arms, the rear sight is about 24" from my eye, so my hyperfocal distance is 48" away. This is 61cm, so my hyperfocal distance is 1.22 meters. Diopter is the inverse of focal length, so to focus at 1.22 meters I need a 0.82 diopter lens.

You need to round down to the nearest 1/4 value, so +0.75.

Have this value added to your distance vision.

Good point in the above post that if you have a strong prescription, vertex distance plays a role, but even there, tell me your prescription and I can run the math to tell you how much it shifts per inch of distance you move the lens.

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Art Neergaard
ShootingSight LLC
www.shootingsight.com
shootingsight@fioptics.com
513-702-4879


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 Post subject: Re: Eyeglass lens
PostPosted: Fri Sep 15, 2017 2:09 am 
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Joined: Wed Mar 24, 2004 6:43 pm
Posts: 1006
The math's is one way of looking at it, all I know is that I want my relaxed focus about 1m in front of my front sight.
This makes my eye focus on the foresight with the least strain for rapid alignment (for faster shooting).
0.5-0.75 does this and it does vary depending on the day, range conditions, light, wellness, night before etc.
Not really for indoor 10m but tints can play a major part outdoors, yellow/brown for low light and grey for bright.


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 Post subject: Re: Eyeglass lens
PostPosted: Fri Sep 15, 2017 7:47 am 
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Joined: Sat Sep 04, 2004 6:04 pm
Posts: 1473
Location: Massachusetts
ShootingSight wrote:
The math is very straight forward, and the answer is distance +0.75 diopters for almost all shooters. If you have exceptionally short arms it might change to a +1.00, but that is rare.

That is your opinion, but it can vary with the individual, whether your math likes it or not. As I pointed out in a different thread on the same subject, this is completely ignoring the effects of depth of field and lighting:

http://www.targettalk.org/viewtopic.php?f=4&t=55721&p=268993

Also, if you wear corrective lenses, the tolerances on most are only good to +/-0.25D, so the exact additional corrective lens required to actually get +0.75D can vary. If your correction is on the low side (close to +0.5D), and the +0.75D lens you add is also close to the low end (near +0.5D), you can be off by as much as a half diopter.

That is why it is good to (A) ignore "the math", (B) experiment, and (C) actually MEASURE your lenses optically. If you blindly lock yourself into the "+0.75" mind set and just go out & buy a lens marked as such, you may not be getting the best results.


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 Post subject: Re: Eyeglass lens
PostPosted: Fri Sep 15, 2017 8:58 am 
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Joined: Fri May 18, 2012 9:37 pm
Posts: 250
Location: Cincinnati, OH
The mathematical solution of +0.75 is derived through optical physics, it is not an 'opinion'. And no, focal point is calculated independently from depth of field, and is not impacted by lighting.

I do grant that it represents a rounding from the actual mathematical solution which I calculated in my post to be 0.82 for my case, and I also agree that it represents an offset from a theoretically perfect distance vision correction which might be incorrect, and I grant that your distance vision correction can change due to hydration and glucose levels through the day.

However, after over 10 years of running a business fitting lenses to hundreds of shooters on an actual shooting range, and seeing that 90-95% fit the +0.75 diopter calculation, I continue to hold the opinion that it is a pretty solid place to start.

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Art Neergaard
ShootingSight LLC
www.shootingsight.com
shootingsight@fioptics.com
513-702-4879


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 Post subject: Re: Eyeglass lens
PostPosted: Fri Sep 15, 2017 12:09 pm 
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Joined: Sat Nov 15, 2008 4:20 pm
Posts: 5094
Location: Scottsdale AZ
I think Dave Levene has it right. I'm old and use a +.50, though.

Really, the thing to do is have your lens setup done by an optometrist in just one lens, focusing on the front sight. Never mind interchangeable setups.

BTW Have your lens "notched" so you can replace it in the frame correctly if you should remove it (or drop it) for some reason.


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 Post subject: Re: Eyeglass lens
PostPosted: Fri Sep 15, 2017 12:32 pm 
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Joined: Sun Jan 16, 2011 6:24 pm
Posts: 358
I have an ophthalmic trial lens set (275 pieces), with lens down to +/- 0.125. (Just an old crazy physician with nothing else to do).

It is not simply +0.75. +0.75 is very good, but that diopter depends on lighting condition, on your accommodation usage over the previous 30 minutes prior to shooting, on how much ciliary muscle spasm you have from watching your iphone video, how dry your eyes are, how anxious you are. A lot can change that optimal front sight clarity.

+0.75 is very good, but might not be good enough for some picky shooters.


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 Post subject: Re: Eyeglass lens
PostPosted: Fri Sep 15, 2017 6:15 pm 
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Joined: Wed Mar 24, 2004 6:43 pm
Posts: 1006
To help clear things up, that +0.5 to +0.75 lens is over and above whatever you distance script is.
If you need distance lens of +1, then your shooting lens would be +1.5 to +1.75.
If your script was -0.5 then your shooting would be 0 to +0.25.
This script may also contain a correction for Astigmatism.
See Dr Wong's article, print it and take it to your Optometrist and if he lets you, with your pistol.


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BULLSEYE SHOOTERS - EyeGuide.doc [36 KiB]
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 Post subject: Re: Eyeglass lens
PostPosted: Sun Sep 17, 2017 11:21 am 
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Joined: Fri May 18, 2012 9:37 pm
Posts: 250
Location: Cincinnati, OH
seamaster wrote:
I have an ophthalmic trial lens set (275 pieces), with lens down to +/- 0.125. (Just an old crazy physician with nothing else to do).

It is not simply +0.75. +0.75 is very good, but that diopter depends on lighting condition, on your accommodation usage over the previous 30 minutes prior to shooting, on how much ciliary muscle spasm you have from watching your iphone video, how dry your eyes are, how anxious you are. A lot can change that optimal front sight clarity.

+0.75 is very good, but might not be good enough for some picky shooters.


Sort of. We may be discussing semantics here, but the +0.75 represents an offset from infinity focus, and that value is calculated based on the distance from your eye to the sight, and does not change. However, to your point, your distance focus might not fall exactly at infinity, but may change based on multiple factors - not lighting conditions, but as you pointed out accomodation usage, ciliary muscle spasms, hydration levels (if you run the math, if your eye diameter changes by 1/100", that is a 0.50 diopter shift), also blood sugar levels, which will impact the glucose levels in the ocular fluid, changing the refractive index.

So while we are both saying that the ideal shooting lens can vary slightly, it is because your distance vision is varying slightly, not because the recommended offset has changed.

Because of this, I do not feel it necessary to take your gun tot he doctor's office. If he does a decent job measuring your distance vision correction, the +0.75 offset is a constant that can be added mathematically. If your eye is 'off' such that he does not measure your distance focus correctly, any measurement made with the gun will also not be correct.

_________________
Art Neergaard
ShootingSight LLC
www.shootingsight.com
shootingsight@fioptics.com
513-702-4879


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