Three dot sights and older eyes?

[shootingsight]

I HAVE THE SOLUTION FOR 'OLD EYES'!

I started a small company that does vision correction for shooters and makes triggers.  I'm a retired engineer who studied some optics, and was an amateur photographer, so when I was in my early 40's and my eyes went and my rifle scores plummeted, I started to look at what was going on.  Once I figured out the parameters to model the human eye as a camera lens, I realized all the photography formulas for calculating exposure and depth of field could be applied to actually calculate what was going on and how to control it.  Funnily enough, photographers get this instantly as soon as you describe the concept.  However eye doctors typically do not, because the human eye is always focusing dynamically, it almost never uses depth of field control.  So while the optical physics of depth of field is something eye doctors will have studied, they never needed to apply it, so it is far from their thoughts.

Shooting is the only human vision activity I have found where you are trying to focus on a near object (your front sight) and a far object (the target) at the same time.  The way your eye used to do this is by focusing between them.  In optical physics, a lens only has one perfect focal distance.  However there is a resolution limit to the photo receptors on your retina (think pixels).  If you take an object that is at the perfect focal length of a lens, and move it slightly further away, it will develop a blur line around it.  However if that blur line is thinner than the distance between two 'pixels' on your retina, you cannot see the blur, so to your brain it is still in perfect focus.  Same is true if you move the object slightly closer than the perfect focal distance.  Bottom line is that your eye does not have one perfect focal distance, but there is some range from slightly closer than your focal point to slightly further than your focal point where everything appears in perfect focus.  This range is referred to as your 'Depth of Field'.

How big that depth of field is, is determined by the aperture size you are looking through.  Smaller apertures give bigger depth of field.  With your eye, the aperture is your pupil.  If you put a smaller hole in front of your pupil, it is the smaller hole that dominates, so this is why merit disks stuck on your glasses for pistol, or peep sights on a rifle work.  This is also why you cannot read the goddam menu in a dim restaurant, because in dim light your pupil expands, and your depth of field diminishes.  If they turn up the lights your pupil constricts and you can focus better.Also the same reason people have trouble driving at night, but not during the day.

Where the depth of field is centered is driven by lens power, which used to be the internal adjustment your eye could make, or else it is the power of the lens in your glasses.

So there are two factors: aperture controls the size of the depth of field range; lens power determines where the depth of field range is centered.

What do you want for shooting?  You want your depth of field range to go from your front sight to your target, so both are in focus.  So you want your lens power to be half way between them, and you want your aperture small.

The problem with the human eye is that as we get older, the lens starts to lose its flexibility, so the internal focusing system loses its adjustment range.  The relaxed human eye will focus at infinity, and you have to exert the ciliary muscle in your eye to pull your focus in close.  As we age and the lens gets hard, the ciliary muscle cannot pull focus in close enough to read, or for intermediate distances it can still focus close, but can only hold the focus close for a few seconds before the muscle fades.  This is why you either cannot see the front sight, or can only see it for a few seconds.

For reading, we have developed the solution of reading glasses and bifocals because the distance to read at is well known at about 18-20", and because there are millions of people who need this, so there is a market.  For shooting, the optical physics and math are exactly the same, but the market was never big enough for the right people to pay attention and solve the formula.  This is where I had my epiphany and applied the photography formulas.

In photography, the point of focus that falls half way between a near object and a distant target is called the HYPERFOCAL distance, and it can be calculated, and from there the required lens power can be calculated.  Without actually going through the math in a post, the answer for a pistol with iron sights is that you want to add +0.75 diopters to your distance vision (which is a few steps less than the weakest reading glasses).  Or if you are 20/20 for distance, you just want a +0.75 lens.  Effectively, adding +0.75 is what your brain/eye used to do when you were young, because the brain just looked for the best overall focus.  Now that you cannot adjust your eye in that close, you can get the same result by adding a supplemental +0.75 lens in your glasses.

You do NOT want to shoot with progressive lenses - get a single vision lens for shooting.  Reason was mentioned briefly above, which is consistency.  Progressive lenses (ie no-line bifocals) have a progressive focal length through the lens, so as the lens shifts on your face, or you tilt your head, your focal point will vary and your point of impact will drift.  If you do want to get a bifocal, get an old fashioned bifocal with a line, and make sure your ADD power is +0.75.

As a cheap start, I had a safety glasses manufacturer make me safety glasses that have +0.75 molded in.  They work great for $25, but the lens quality is your standard molded safety glasses quality.  It works, but you can do better with a decent pair of eyeglasses.  Best I can do on a pair of single vision glasses for someone is about $60 including AR coating, but your local Wal-Mart eye doc can possibly do better.  Just remember, you want single vision glasses with your distance correction with an ADD of +0.75 (that is the eye doc term for adding power to shift your focus close).  I'm happy to consult with anyone that has a prescription and isn't sure how to adjust it - email me at art@shootingsight.com

As an aside, few people know what diopters actuially are, but it is simple and useful to know.  Diopters are the inverse of the lens focal length, in meters (yah, the fact that it is metric makes it confusing).  Here is how it works: a 2.00 diopter lens will focus at 1/2 meters.  A 3 diopter will focus at 1/3 meters.  You can go fractional as well: 1/2 diopter will focus you a 2 meters, and 0.75 diopters (3/4) will focus you at 4/3 meters, or 1.33 meters.

So with a calculator (meters/0.0254 = inches; inches * 0.0254=meters) you can take a task, measure the distance from your eye to the task, and figure out what power reading glasses are ideal.  Reading is 20" from you, that is 0.508 meters away, so 1/2 meter.  That means for reading you want +2.00 diopter lenses, or if it is 18" it works out to +2.25.  Working on small stuff right in front of my nose is about 12" away, which is 1/3 meter, so +3.00 diopters.  Watching TV across the room is 8 feet away, about 2 meters, so I need 1/2 diopter - +0.50.  Working on my lathe is about 1 meter away, +1.00 diopter.  My computer monitor is 24" away - 1.65 diopters, so I could go +1.50 or +1.75.  Usually, you round down, because your eye muscle can add power.

The benefit of this is that by using the correct glasses your eye muscle stays relaxed and does not fatigue.

Bottom line: for irons on pistol and carbines, like the AR, you add +0.75, for long rifles, like M1, M14, likely for trap guns, you only add +0.50.

Also, I take self adhesive aluminum tabs and drill 1/16" holes in them.  You can stick one on your glasses and you will be amazed at the improvement in focus, just because your depth of field is increased.  You ideally want both an increase of DoF, and a lens to get it properly centered, but if you do just one or the other it will still help.  So these patches are one step, not a complete solution.  Anyhow, I give these things away for free.  If anyone wants one, email me with your mailing address and I'll drop one in an envelope for you.

Art Neergaard
ShootingSight.com

[Rmach]

I HAVE THE SOLUTION FOR 'OLD EYES'!

I started a small company that does vision correction for shooters and makes triggers.  I'm a retired engineer who studied some optics, and was an amateur photographer, so when I was in my early 40's and my eyes went and my rifle scores plummeted, I started to look at what was going on.  Once I figured out the parameters to model the human eye as a camera lens, I realized all the photography formulas for calculating exposure and depth of field could be applied to actually calculate what was going on and how to control it.  Funnily enough, photographers get this instantly as soon as you describe the concept.  However eye doctors typically do not, because the human eye is always focusing dynamically, it almost never uses depth of field control.  So while the optical physics of depth of field is something eye doctors will have studied, they never needed to apply it, so it is far from their thoughts.

Shooting is the only human vision activity I have found where you are trying to focus on a near object (your front sight) and a far object (the target) at the same time.  The way your eye used to do this is by focusing between them.  In optical physics, a lens only has one perfect focal distance.  However there is a resolution limit to the photo receptors on your retina (think pixels).  If you take an object that is at the perfect focal length of a lens, and move it slightly further away, it will develop a blur line around it.  However if that blur line is thinner than the distance between two 'pixels' on your retina, you cannot see the blur, so to your brain it is still in perfect focus.  Same is true if you move the object slightly closer than the perfect focal distance.  Bottom line is that your eye does not have one perfect focal distance, but there is some range from slightly closer than your focal point to slightly further than your focal point where everything appears in perfect focus.  This range is referred to as your 'Depth of Field'.

How big that depth of field is, is determined by the aperture size you are looking through.  Smaller apertures give bigger depth of field.  With your eye, the aperture is your pupil.  If you put a smaller hole in front of your pupil, it is the smaller hole that dominates, so this is why merit disks stuck on your glasses for pistol, or peep sights on a rifle work.  This is also why you cannot read the goddam menu in a dim restaurant, because in dim light your pupil expands, and your depth of field diminishes.  If they turn up the lights your pupil constricts and you can focus better.Also the same reason people have trouble driving at night, but not during the day.

Where the depth of field is centered is driven by lens power, which used to be the internal adjustment your eye could make, or else it is the power of the lens in your glasses.

So there are two factors: aperture controls the size of the depth of field range; lens power determines where the depth of field range is centered.

What do you want for shooting?  You want your depth of field range to go from your front sight to your target, so both are in focus.  So you want your lens power to be half way between them, and you want your aperture small.

The problem with the human eye is that as we get older, the lens starts to lose its flexibility, so the internal focusing system loses its adjustment range.  The relaxed human eye will focus at infinity, and you have to exert the ciliary muscle in your eye to pull your focus in close.  As we age and the lens gets hard, the ciliary muscle cannot pull focus in close enough to read, or for intermediate distances it can still focus close, but can only hold the focus close for a few seconds before the muscle fades.  This is why you either cannot see the front sight, or can only see it for a few seconds.

For reading, we have developed the solution of reading glasses and bifocals because the distance to read at is well known at about 18-20", and because there are millions of people who need this, so there is a market.  For shooting, the optical physics and math are exactly the same, but the market was never big enough for the right people to pay attention and solve the formula.  This is where I had my epiphany and applied the photography formulas.

In photography, the point of focus that falls half way between a near object and a distant target is called the HYPERFOCAL distance, and it can be calculated, and from there the required lens power can be calculated.  Without actually going through the math in a post, the answer for a pistol with iron sights is that you want to add +0.75 diopters to your distance vision (which is a few steps less than the weakest reading glasses).  Or if you are 20/20 for distance, you just want a +0.75 lens.  Effectively, adding +0.75 is what your brain/eye used to do when you were young, because the brain just looked for the best overall focus.  Now that you cannot adjust your eye in that close, you can get the same result by adding a supplemental +0.75 lens in your glasses.

You do NOT want to shoot with progressive lenses - get a single vision lens for shooting.  Reason was mentioned briefly above, which is consistency.  Progressive lenses (ie no-line bifocals) have a progressive focal length through the lens, so as the lens shifts on your face, or you tilt your head, your focal point will vary and your point of impact will drift.  If you do want to get a bifocal, get an old fashioned bifocal with a line, and make sure your ADD power is +0.75.

As a cheap start, I had a safety glasses manufacturer make me safety glasses that have +0.75 molded in.  They work great for $25, but the lens quality is your standard molded safety glasses quality.  It works, but you can do better with a decent pair of eyeglasses.  Best I can do on a pair of single vision glasses for someone is about $60 including AR coating, but your local Wal-Mart eye doc can possibly do better.  Just remember, you want single vision glasses with your distance correction with an ADD of +0.75 (that is the eye doc term for adding power to shift your focus close).  I'm happy to consult with anyone that has a prescription and isn't sure how to adjust it - email me at art@shootingsight.com

As an aside, few people know what diopters actuially are, but it is simple and useful to know.  Diopters are the inverse of the lens focal length, in meters (yah, the fact that it is metric makes it confusing).  Here is how it works: a 2.00 diopter lens will focus at 1/2 meters.  A 3 diopter will focus at 1/3 meters.  You can go fractional as well: 1/2 diopter will focus you a 2 meters, and 0.75 diopters (3/4) will focus you at 4/3 meters, or 1.33 meters.

So with a calculator (meters/0.0254 = inches; inches * 0.0254=meters) you can take a task, measure the distance from your eye to the task, and figure out what power reading glasses are ideal.  Reading is 20" from you, that is 0.508 meters away, so 1/2 meter.  That means for reading you want +2.00 diopter lenses, or if it is 18" it works out to +2.25.  Working on small stuff right in front of my nose is about 12" away, which is 1/3 meter, so +3.00 diopters.  Watching TV across the room is 8 feet away, about 2 meters, so I need 1/2 diopter - +0.50.  Working on my lathe is about 1 meter away, +1.00 diopter.  My computer monitor is 24" away - 1.65 diopters, so I could go +1.50 or +1.75.  Usually, you round down, because your eye muscle can add power.

The benefit of this is that by using the correct glasses your eye muscle stays relaxed and does not fatigue.

Bottom line: for irons on pistol and carbines, like the AR, you add +0.75, for long rifles, like M1, M14, likely for trap guns, you only add +0.50.

Also, I take self adhesive aluminum tabs and drill 1/16" holes in them.  You can stick one on your glasses and you will be amazed at the improvement in focus, just because your depth of field is increased.  You ideally want both an increase of DoF, and a lens to get it properly centered, but if you do just one or the other it will still help.  So these patches are one step, not a complete solution.  Anyhow, I give these things away for free.  If anyone wants one, email me with your mailing address and I'll drop one in an envelope for you.

Art Neergaard
ShootingSight.com

Very interesting, thank you! The focus on my progressive lens does drift while firing repeatedly, especially when my head is tilted back. I found an old pair of reading glasses that work well for that front sight focus. I will try them out on my next range visit.

[shootingsight]

Sorry I wasn't more clear.

As you go up in diopter power, your focal point moves closer.  As you go down, it moves further away.

Typically, your front sight is maybe 24" from you, so using my formula, 24*.0254 = 0.61 meters, so you would use a 1.5 diopter lens to see a perfect front sight.  Good news is that this is in the range of dime store reading glasses, so you can actually give it a try as an experiment.  It will give you a FANTASATIC front sight, and this is typically the answer people get if they go to the eye doctor.

The bad news is that your target will be so blurry, you cannot see it.

Exactly the magic of what I have discovered is that to see the target and the sight together at the same time, it is critical that your eye is focused at a point half way between the two.  If you go stronger, you'll get a better front sight but the target blurs.  If you go weaker, you get a better target, but the front sight blurs.  Indeed, from before I figured out the math, I sell test frames that have 5 different power lenses in them, from 0.25 to 1.25 in 1/4 power steps, and you can aim your pistol and hold these lenses in front of your eye and run the power up/down and see the focal point change.  Some people still buy them to see the effect.

So the +0.75 is pretty well exact in optical physics.  If you own old reading glasses, you can try it to see, but just don't get disappointed if the result is less than ideal.

[Beak Boater]

Very interesting, my situation was the same as most. Front sight blurry, target clear. I could still shoot well but I wondered if I would shoot better if the front sight was clear and the target a little fuzzy. Went with a 1.25 which gave me a crystal clear front sight, but a very fuzzy target picture especially at longer distances. Also in low light situations. While shooting at the range I will experience eye fatigue. Would going down to 1.0 or .75 help with eye fatigue? I know I will give up a little clarity of the front sight, and the target will be in better focus. But I guess the only way to know is to experiment. Thanks for the insight.

[shootingsight]

You should not get eye fatigue from using overly strong glasses, only from too low power.

The eye muscle is a 1-way muscle that acts against the elastic lens in your eye.  You exert the muscle to bring your focus in, and when you relax the muscle, the elastic nature of the lens pulls the focus back out.  As you get older, the lens loses its elasticity, and the muscle has to work harder to pull your focus in.  So if you spend a day at a desk. or even a few minutes staring at a sight, the eye muscle will fatigue from holding the lens in a tensed position.

Conversely, if you go too strong, the target will be blurred, but your eye will be fully relaxed because your brain is trying to move your focus out further than the elasticity of the lens will take it.

I think being too strong is probably better for you.  What you are after above all is consistency, as with much else in shooting.  If your eye muscle is straining, you will get one focal point for the first few seconds after you aim, but the muscle is fatigued, so it will fade, and your focal point will drift both in the time to take a single shot, and across the time it takes to shoot a match.  The problem with drifting focus is that as the width of the blur line around the front sight changes, the post appears bigger/smaller.  You can still rely on the symmetry of centering the bull over the post, regardless of focus, so not so much impact on windage estimation, but you only have one top/horizontal edge to judge elevation, and that gets messed up.  Typically, symptom of a shooter struggling with vision in metallic sights is that they string their shotgroups vertically due to drifting focus.

If you want to go with the cheap solution, I sell safety glasses that have +0.50, +0.75, and +1.00 molded in for $25.  So the utility of the +1.25 reading glasses experiment is really to demonstrate the validity of the optical theories I am describing.

[Psyop96]

Typically, symptom of a shooter struggling with vision in metallic sights is that they string their shotgroups vertically due to drifting focus.

I get your drift! I have a fair amount of strings like these. Great discussion here. I think I have discovered some of these principles by trial and error without knowing the more technical aspects presented here.

[dominic135]

I'm sorry but I just can't see the point of upside down glasses. Maybe my eyes aren't bad enough but my problem is, I can see the front sight with the reading lens, but not the target. I can see the target with my distant lens... but not the front sight! I wrote about the Merit Optical peep sight above. When using it, I can see both distances with equal clarity. Isn't that the real problem? Isn't that the reason peep sights are used on military rifles? I mean even if your vision is perfect, you have to deal with your lens adjusting back and forth when sighting a target? The peep sight relieves the shooter of the constantly refocusing eye.

[shootingsight]

The point of upside down glasses is to get to see the front sight without having to tilt your head.  However, as you pointed out, with regular reading power bifocals, you get a great front sight, but your target is too blurry.  You need to dial in the correct lens power.

For the merit disk, as I pointed out in my first post, there are two factors.

1.  Size of your depth of field, which is driven by aperture size.  This is what the merit disk helps.
2.  Lens power, which determines where your depth of field is centered.  If you are young, the eye muscle can do this.  If you have presbiopia (old eyes) you need a supplemental lens to help.

Doing just one or the other of the above will help versus just using your eye.  But they are independent of each other, so ideal is to optimize both.  The fact that you can see the target with your distance lens, but not the front sight, means your eye cannot adjust to the hyperfocal distance.  You might be able to get part way there, such that the added depth of field makes it look acceptable, but ideally you want to adjust your focus in, without having to strain the eye muscle.

[Rmach]

I went to the range Friday and fired my Henry .357 Big Boy for the first time. I wore my progressive lens glasses that I use for pistol shooting.  These are the glasses that I have to tilt my head back for pistol aiming. Anyway, the Henry has a barrel mounted Skinner peep sight that I installed before firing it for the first time because my old eyes won't work well with a factory buckhorn rear sight. The peep sight worked fairly well for me since I haven't fired a rifle in over 40 years. Standing position with target set at 25yds:

[WilburWildcat]

I have learned the same lessons described by ShootingSight.
My 60 year old eyes require +1.75 for basic reading.
That is way too strong for the front sight at arm's length. 
For me, +1.00 gives a perfectly sharp focused front sight; but a blurry target.  Until reading the link above for SSP eyewear, I had not found a tinted +1.00 for use outdoors.
I would be interested in trying the +0.75 for improved focus of both the front sight and the target.  Shootingsight, How do I order a pair?

[shootingsight]

www.shootingsight.com

https://shootingsight.com/product/safety-shooting-glasses/

[1SOW]

Interesting. 
For my 71 year old eyes the VA Optometrist (a shooter)  tests were done with my arms extended holding a pencil out to front sight distance as the first "in focus" point with the primary lens and then tested for focus at 20 yards +/-.  She put in a very small and low reading lens (with the line)  and the rest of the glass will focus on both the front sight and the target at about 20 yards.  I needed the reading portion to sign up and/or study the stage descriptions at the matches.
 These glasses are awkward around the house but work really well at the range.   She also gave me a prescription for "regula"r glasses so I don't have to tip my head UP to read at closer distances
They seem to meet your findings.

P.S.  the shooting glasses also work best with a P.C..  I'm wearing them now. "I can see clearly now". 

[Vinny]

Fascinating stuff. I've been experimenting similarly. 67 year-old eyes.

However, for defensive purposes my instructor recommended I try a red dot reflex optic. WOW!  Bulls-eyes again at 20 yards with only non-script safety glasses! It does take some getting used to looking through the optic lens with both eyes open and just focusing on the target. But the red dot appears brightly at POA. And of course you need a good red dot $200+ to withstand the high G forces of a moving slide so first I tried a $40 Browning reflex on my 22's (SW Victory and Ruger MK IV) where the optic mounts to the non-moving receiver. That convinced me I was on the right track. 

The lower the optic mounts, the easier it is to bring the gun naturally up to POA. That's the concept in milling the slide to get the optic lower. However, that adds even more cost.

Because I have several CZ 75 SP-01's I don't want to spend that much $$. So, I've combined a JPoint from JE Enterprises (~$250) with a Leupold CZ 75 Mount p/n 170903 (~$25) that also fits the JPoint . Some guys like the Burris Fast-Fire 3 or Vortex models and there's others, but what I like about the JPoint is it's ultra-low profile and co-witness sight notch and with the mount it sits only ~ .375 above the slide. No costly milling required. Now...all I need to complete this is the right height taller Dawson FO front sight to co-witness and I'll be in for just over $300.

IMHO..For a defensive gun, shooting with both eyes open without the need for special lenses is a huge advantage in putting rounds on target (possibly multiple targets) quickly. Just presenting another option for Older Eyes. Note how low the optic sits on the slide with this combo:

 

[David0408]

I'm 46 and my eyes are starting to go too. I have to use +125 to read anything.
My question is, what happens if you are in a situation and you don't have your shooting glasses on?

[delphidoc]

I'm 46 and my eyes are starting to go too. I have to use +125 to read anything.
My question is, what happens if you are in a situation and you don't have your shooting glasses on?

My goal would be to avoid the situation in the first place, if possible. Option 2 would be to leave that situation, if possible.

If Option 2 isn't feasible it would probably be because your threat is so close there's no way to get away without confrontation. If it's that close you don't need to aim. I posted somewhere above that I recently tried pointing a gun at a target at 6-7 yards without aiming. I was pleasantly surprised how accurate I was with just pointing.

Cliff's Notes version of above: just point the gun and empty the mag. You'll hit it anyway.