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target clarity

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john bickar
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Post by valbern67 6/17/2019, 8:09 am

How clearly should one see the targets at 50 and 25 yards?  What is a reasonable expectation of focus, especially at the center or X-ring? I'm trying to figure out if my regular contact lenses are sufficient, or if I should get glasses with sharper distance?

I'm currently weraing monovision contacts, and my dominant eye has the distance lens but my targets are blurry at 50 yds and less so at 25 yards.  Been thinking about getting prescription shooting glasses, but they tend to be really expensive. Is there an extra lens for extra magnification I could wear over the right eye over my normal glasses?

Thanks!

Val

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Post by mikemyers 6/17/2019, 8:53 am

Red dot sights, or steel?
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Post by valbern67 6/17/2019, 9:14 am

Either, really. But I shoot more red dot.
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Post by willnewton 6/17/2019, 9:30 am

Dot should be, round, sharp, and just one dot.

Front sight should be sharp and in focus.

Target should be blurry.

You don’t get prescriptions to bring the target into focus.  You get one to bring the pistol sights/dot into focus.

If you have the target in focus then you aren’t looking at your sights.

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Post by valbern67 6/17/2019, 9:33 am

👍
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Post by shootingsight 7/2/2019, 12:26 pm

Since the distance between your sights is much smaller than the distance between your sights and the target, sight alignment is MUCH more critical than alignment with the target.  This is why people want SOME amount of blur on the target, and sharper sights.

Typically, a good starting point for focus is to use +0.75 diopters added to your distance prescription.  This will place your relaxed focal point between your rear sight and the target, so you get similar rear and target focus, and your front sight is a little sharper than the others.

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Post by mikemyers 7/2/2019, 2:34 pm

This may sound like a silly question.....    I had cataracts, and vision issues, so I started using red dot sights.  Then I got the cataracts corrected, and at the eye hospital I volunteer at in India, I had three pair of glasses made for three specific distances:

  • 24" eye to steel front sight, two hand shooting
  • 30" eye to steel front sight, one hand shooting, and
  • infinity. distance prescription, targets, red dots, the moon, etc.


For a test, I went to the range with my Les Baer Premiere II, steel sights, and shot it at sub-6o'clock hold as I learned from people here.  This was two-handed shooting, as when I tried one-handed, the gun felt too heavy for me to keep steady.  Need more practice.  It was a bright sunny day, outdoors, and probably close to 100 degrees.

Everything went better than expected, and once I got to do things correctly, the results are about equal to my ability to hold.  I think I can improve on this with practice, but that's not what I'm asking about here.


Now, on to my question.  While the front sight at 24" was perfectly sharp, the target was still so sharp I found it distracting.  If I think of this in terms of photography, I could get a pair of glasses wit a prescription closer than 24", and hopefully the front sight will still be crisp, but the target will be a blur.  


Or, put more simply, how does one get a sharp front sight at 24", and make the target a blur at 25 yards?  I suppose I could change to 50 yards, if there isn't a good way to do this at 25.
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Post by Jack H 7/2/2019, 3:40 pm

The bull usually blurs.  But it does not have to as long as the front is really clear, and you really keep your eye on it.  Increased depth of field might be something about your cat surgery and Rx in combination.
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Post by shootingsight 7/2/2019, 5:22 pm

Diopters, as in lens strength, are the inverse of focal length in meters, so 2 diopter added to your distance vision will focus you at 1/2 meter, 3 diopter at 1/3 meter, and so on.  1/2 diopter will focus you at 2 meters.

If you add 0 diopters, you are focused on the target.  If you add +1.50 diopters, you are focused at 66cm (26 in)  this is square ON the sights (actually between the rear and the front for most people.  But it is WAY too strong.  It gives you fantastic sights, but much too fuzzy target.

For most people, the half-way power of +0.75 is the best solution.  3/4 diopter means you are focused at 4/3 meter or 1.33.  Optically, this is the half way point.  People have experimented with going to +1.00.  This will blur the target, but if you have adequate light such that you can reduce your aperture slightly, it can restore sufficient target clarity, and you will see very nice sights.  I think the next step of +1.25 is possible, but only if you are shooting outdoors in bright light, so you can use a really small aperture.

In photography, this concept of focusing half way between two objects is called the hyperfocal distance.

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Post by bruce martindale 7/2/2019, 5:33 pm

But....we really WANT to look at the target, and it's the wrong thing to do.Especially after the 6 fairy visits the visible regions.

The only issue I have with Wills picture is it isn't a sub six. That tangent hold promotes "measuring" to get it just right. And that causes trigger inhibition. As an extensive user of iron sights, l am looking for a bar of white on top of the sights that is as wide as the side bars. This lets me focus on sight alighnment during the pull and l avoid making it perfect. Good enough trumps perfect.

Also center holds are good because you really need to focus on sights, yes there is enought contrast between target background and sights. Floating in and out of the black edge give me distortion.

Regards

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Post by DA/SA 7/2/2019, 5:49 pm

I've been fighting the vision thing since I started this Bullseye stuff.

I just switched to using +2.50 to get a clear, round dot, and the target is pretty fuzzy, but doable at 25 yds., which is kind of a good thing. This would be +1.25 added to my distance vision. The big issue now is that I see a clear reflection of myself in the scope! Also I'm using a polarizing filter and now see every little defect in it as well as any dust particles on the scope lens. It's kind of distracting...

Any less than +2.50 and the dot is a big amoeba.

As for iron sights, anything less than +2.50 and the sights are just a blob. With the +2.50 the front sight is perfectly clear but the target is nearly indistinguishable.

Any suggestions there would be very welcome! My Ophthalmologist isn't a gun guy at all...

I'm also 6'5" and my front sight with irons is 36" from my eye, with a dot scope being about 30"...


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Post by mikemyers 7/2/2019, 6:46 pm

shootingsight wrote:Diopters, as in lens strength, are the inverse of focal length in meters, so 2 diopter added to your distance vision will focus you at 1/2 meter, 3 diopter at 1/3 meter, and so on.  1/2 diopter will focus you at 2 meters.

If you add 0 diopters, you are focused on the target.  If you add +1.50 diopters, you are focused at 66cm (26 in)  this is square ON the sights (actually between the rear and the front for most people.  But it is WAY too strong.  It gives you fantastic sights, but much too fuzzy target.

For most people, the half-way power of +0.75 is the best solution.  3/4 diopter means you are focused at 4/3 meter or 1.33.  Optically, this is the half way point.  People have experimented with going to +1.00.  This will blur the target, but if you have adequate light such that you can reduce your aperture slightly, it can restore sufficient target clarity, and you will see very nice sights.  I think the next step of +1.25 is possible, but only if you are shooting outdoors in bright light, so you can use a really small aperture.

In photography, this concept of focusing half way between two objects is called the hyperfocal distance.

  • Maybe you, or someone who understands diopters, could translate this prescription into bullseye information.
  • My right eye has been corrected to close to perfect distance vision.
  • This prescription was carefully prepared by my reading a card held 24" in front of me, the distance to my front sight on a 1911.
  • It works exactly as I expected - the front sight is perfect.
  • I would prefer the target to be more blurry, but without losing clarity for the front sight.
  • What prescription would be better for bullseye, for me, front sight sharp, but preferably target blurry.
  • I have an IOL in my eye, so it does not focus at all; it's fixed.
  • (For the left eye, I got a prescription that allows me to see what I'm doing on the workbench, without needing to change glasses.)
  • (I would love to know how you started with this, and translated it into something an ordinary person would understand, but what I need the most is the actual prescription so the next pair of glasses will be correct.)


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Post by shootingsight 7/2/2019, 11:12 pm

If +2.0 is perfect for clarity at 24", it means the lens you are looking through is about 1.50 diopters stronger than your distance vision needs. (24" = 0.61m; 1/0.61 = 1.64 diopters), so your distance prescription is about a +0.50.  Very good news for you is that with no astigmatism, and relatively mild correction, your correct shooting lens falls square in the middle of the range of inexpensive reading glasses that you can buy (ie about 1.25 to 3.00 range).  If you want more fuzz on the target, I'd go to a +2.25.  This will bring your focal point back to 22.5", so between the front and rear sight, so they will still be very good, and it will fuzz the target slightly.  If you want to be bold, a +2.50 will bring your focus to 20" and will fuzz the target even more.

As I said, these powers are inexpensive and commonly available to test.  They are not impact resistant, so be cautious about actually shooting with them, but they will let you experiment.

Note that this optical math is calculated for iron sights, not for red dots.


Last edited by shootingsight on 7/2/2019, 11:30 pm; edited 1 time in total

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Post by shootingsight 7/2/2019, 11:14 pm

+1 on the polycarbonate lens - PC is impact resistant and naturally filters out UV.

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Post by mikemyers 7/2/2019, 11:42 pm

This is slowly starting to make sense to me.  So I should go to the local drugstore and get reading glasses  for +2.50. and +2.25, and see if they give me a sharp front sight in front of a blurry target?   I won't shoot obviously.

Thank you - big help!   I sent a copy of what you wrote to my eye doctor back in India.
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Post by shootingsight 7/2/2019, 11:49 pm

Yes, get the drugstore glasses.

Tell your eye doctor that the typical goal is to focus at the hyperfocal distance of the rear sight, that is a point that is optically at the average of the rear sight and the target, so your eye's natural depth of field is evenly split between the target at optical infinity, and the rear sight.  This is usually a good starting point for shooters.

Now, the needs you describe are outside the norm.  You claim you are focusing at 24", right ON the front sight, and you still feel the target is too sharp.  So since this departs from the norm of hyperfocal focus, I recommend that you experiment, but as stated you are lucky enough that cheap reading glasses will get you information to figure out what you like.

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Post by mikemyers 7/3/2019, 1:00 am

You gave me lots of good ideas to work with.  I have one pair of inexpensive reading glasses (the other two pair I had I gave away).  Tried them but I didn't like the effect.  So, I got my own reading glasses and put them on.  This is indoors, so it's not a fair test, but the front sight was still quite clear, and the "background" (my room an big screen TV) were nicely blurred.  

I'm not really sure how "sharp" the rear sight was - all I was looking at was the gaps on either side, and that the three sight tops were in line.  

If I get to the range tomorrow, as I hope to, I'll test the reading glasses, just for vision, not for shooting.

(All of what I'm describing is with open sights.  The OP said he's mostly using red dot.  I don't understand the question, as my distance prescription makes both the dot and the targets sharp.  I have to pick which one to concentrate on.  Lately I'm trying to concentrate on the target, and center the "blur" of the red dot centered over the target as best I can.)
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Post by Dr.Don 7/3/2019, 9:36 am

Don't forget that depth of field (or depth of focus at the retina or film plane) is dependent upon the aperture.  In bright sunlight your pupil "stops down" to a small aperture and depth of field is increased, so the target will look less blurry in this case.  On a marginally lit indoor range the pupil will open wide and the target appears more blurry.

Since you cannot control the aperture (pupil size) directly, you really can't adjust this depth of field issue.
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Post by shootingsight 7/3/2019, 11:19 am

On the contrary, you CAN control aperture size.  I make little aluminum foil stickers with holes in them that you can stick on your shooting glasses.  As long as the hole is smaller than your pupil, it will improve your depth of field, and importantly make it constant, so your depth of field is unchanging.

I'm working on a hypothesis that if you use +1.5 added to your distance prescription, it will put your focus between the front and rear sights, so within the resolving ability of your eye, they will look perfect, then step down your aperture to get the desired target clarity (no aperture with +1.50 add is likely too blurry).

THe limit of his concept is if the range is bright enough, because small apertures let through less light.

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Post by Dr.Don 7/3/2019, 1:11 pm

You can indeed use an external aperture, aluminum foil or otherwise.  But your internal aperture (pupil) opens because your eye wants/needs more light.  So using an external aperture in a low light situation like a marginal indoor range makes things darker and arguably increases eye strain.  You rightly noted that in your bottom line regarding "bright enough".  I have no argument against external apertures and have used them successfully in the past.  Your approach with the aluminum stick-ons is one I have not encountered before.
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Post by DA/SA 7/3/2019, 1:17 pm

I've made many of them from black plastic static cling film. Easily moved around, or to different glasses.

Haven't hit on the right strength glasses to use with one for Bullseye yet though.
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Post by shootingsight 7/3/2019, 2:43 pm

You are correct - availability of light is the ultimate factor.  However my theory is that you have some lattitude.  I believe your pupil dilates based on the average brightness.  So in a dark range where there is a bright spot light on the target, your pupil will be oversized for the target as it averages in the unlit area.

Also, be aware that if you use an opaque blinder for your non-shooting eye, your pupils will over dilate.  Your two eyes dilate together, based on the average they see, so if one eye sees light, and the other dark, they will both dilate half-way.  You can actually stand in front of a mirror and cover one eye with your hand.  As you cover/uncover the one eye, you will see the pupil in the other eye dilate and constrict.

Bottom line, I think you can usually step your aperture down from what your eye naturally sees - how far is likely a shooter preference.

If anyone is interested, I developed an excel spreadsheet that calculates the theoretical 'circle of confusion' or the width of blur line on your retina, so you can input sight radius, lens strength, and aperture size, and it will plot out blur line on target, front sight,and rear sight.  If anyone is interested, email me: art at shootingsight.com

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Post by mikemyers 7/3/2019, 4:45 pm

I'll send you an email later this evening - would like to check it out.

I have no reason to want "more" depth of field - I want less.  I want the target to be a blur, and the rear sight to be razed sharp.  Your earlier suggestion most likely solved that for me.  I also prefer that everything be bright.  I try to do all my shooting outdoors, now that I can.
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Post by shootingsight 7/6/2019, 4:18 pm

People like brightness, as it helps you focus better.  Unfortunately, your brain does not understand why, so it reacts incorrectly.

When you learn that you can read the menu better in a dim restaurant if you add more light, your brain thinks it is the increased light that does it, so a lot of rifle shooters I know want to go drilling out their apertures to let in more light, so they can focus better.  Indeed, it is the other way around.

What is REALLY happening in that dim restaurant is that adding more light makes your pupils constrict, improving your depth of field, so when you can't quite focus at arm's length, the improved depth of field lets you focus well enough.  So the real solution for shooting is exactly to make the aperture smaller, and not go for the brightness.  Obviously there is a limit, but for the most part, a smaller aperture is better.

Two other restaurant tricks: if you forgot your reading glasses, ask the waiter.  The hostess desk always has a box of assorted reading glasses that people forgot on the table, so you can just dig through the lost/found box to get a set you need.

Also, if your glasses are dirty, ask for a napkin with a few drops of vodka on it.  Vodka is as close to water and alcohol as you will find, so it is a really good glass cleaner if you are willing to waste it on that.

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Post by mikemyers 7/6/2019, 4:43 pm

Maybe my eyes are strange, but regardless of whether I'm at a restaurant or the range, if I'm wearing the appropriate glasses, everything at the appropriate distance is sharp.  Adding more light makes it easier, but I always thought this was due to more contrast.  Never really thought about it.

When I dry-fire, and look at my perfectly sharp front sight in front of a medium gray wall, it is difficult.  When I move a little bit, so the front sight is in front of a lighter area, everything is so much easier.   When I try to line up my steel sights in front of a bullseye, it's difficult, but when I shift to sub-6 hold it is so much easier.  

I had my cataracts removed, so my eyes can not focus.  I think what you're saying would work as you describe for people with normal eyes, that can and do focus.


As of this afternoon, I'm using this concept on purpose for dry firing.  I deliberately place my front sight in front of things that vary as to how light they are.  I would like to be able to adjust the sights correctly even when there isn't much light.
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