Help with sighting suggestions

First topic message reminder :

Good day, new here and new to bulls eye shooting.

I have very bad eyesight, over 20/200 in both eyes uncorrected. I also wear bi-focals. With a good adjustment to my prescription I still can only see one thing at a time. I can either see the sights or I can see the target, not both. I can get a good alignment, but have no idea where I'm aiming. Or, I can see the target, but can't get an alignment. I've checked out some suggestions with making the dominant eye lens for close up and the other for long distance. There are some other suggestions with the glasses set up as well. My problem is I do not have a dominant eye. I can only shoot with one eye open. I've practiced to have both open, but both are fighting for dominance and it throws the image off.

With my typical +0.75 diopter my front sight is in focus. If I allow my eye to shift focus to the rear sight, the rear sight is in focus; but I am slightly straining my eye to keep the focus. So if I focus on one of them, the other is barely out of focus. The target at 25 is blurred, but not excessively. At 50 yds the target is extremely blurred.
Jon

To clarify: I think there are two different issues being discussed.  The first is the focal balance between sights and target that is driven by the ADD value, and I think there is consensus that many shooters settle between about +0.50 and +1.00.

The other issue is degree of total blur in the sight picture, which is driven by pupil size/aperture size.  Since different people have different pupil sizes, and individual pupil sizes vary with ambient lighting conditions at different ranges, it is difficult to show what one individual can see, so I have really photographed one example of how it would look if someone had a 1/4" pupil.  As stated, even this is not perfect, as spacing of cones on the retina varies across people I have seen cone concentrations at the center of the fovea as low as 80,000/mm2, up to 325,000/mm2.

So here is the entire matrix of pictures that I took - you can choose which column represents what you see most closely, so you can scan up/down to see the effect of changing the ADD of the lens you use.

I tried the transparent blinder suggestion using a piece of plastic milk carton. I found it made sighting less stressful on my eyes, so I was able to concentrate on the sights better. The downside was my eyes were still fighting for dominance and the image kept jumping back and forth from the sights to the blinder. I think I'll try a blacked out blinder next. I'll place it on the lens, not the eye, so light can still reach the iris and see how that works.

When I have a chance I'm going to check out the suggestions for the focal adjustments on my glasses. I'll get dedicated wrap-arounds for this. I did notice that with the blinder I could see the distortion the glasses were creating as I tried to focus one-handed and looking out the side of the lens. I'll have to get a correction on that as well.

Most of our bullseye shooters are probably between the ages of 40 to 70 years old. Those younger typically have little problems seeing the front sights. We commonly use millimeters to measure pupil sizes. The following are the typical pupil sizes relating to age.

age:   pupil size(mm):
40      4.0
50      3.5
60      3.0
70      2.5

https://nursekey.com/wp-content/uploads/2016/07/C1-MMU13.gif

https://starreloaders.com/edhall/nwongarts.html

You can easily compare your pupil size by using the chart above.  One can compare the pupil sizes within the cornea.  I included an article on the "Ideal Pupil" that was written many years ago but it always comes in handy during our discussions which arises time and time again.

The majority of the camera illustrations are not indicative to these pupil sizes. I believe it may be difficult to produce the same type of illustrations but showing how the sight pictures would look with these 4 pupil sizes, we can appreciate more accurate illustrations.  Don't be too concern with how the pupils appear under dimmer lighting.  I have 3 mm. pupils and to satisfy my curiosity many years ago, I went to our range to shoot at night while using a +1.25D add at 50 yds and had no problems seeing the bullseye as I was trying the sub six hold.  However, thank you for these illustration.  The 1/4" pupil in the illustration equates to 6.35 mm. which is uncommonly large.

It is true we can quantify lens power along with pupil sizes, however, the missing item of importance is human visual perception. I experienced this all the time while I was in practice. With the same visual acuity, some may have no visual complaints while others have many. This is why I cannot comment on the ideal shooting lens add because everyone is different. Also, I had mention "Optical Infinity" many years ago but was quickly reminded that shooters "see" differently at 25 yards vs 50 yards.  Jon Eulette mentioned this also, the blur is different.

Norman H. Wong, O.D.

Had cataract surgery in both eyes. Now 20/20 and 20/30 for distance uncorrected. (Obviously, no ability to focus.) 

For dots and shotgun, I use off the shelf bifocal safety glasses with the only correction being reading in the bifocal. For irons I use off the shelf safety glasses with appropriate front site/target correction. 

I'm considering buying prescription safety/shooting glasses for dots and shotgun. (i.e. distance correction) I do want a reading correction either as a bifocal or progressive. Thoughts on bifocal vs progressive lenses? Do bifocals have the best correction through a larger area of the lens compared to progressive? I'm comfortable with progressives and bifocals, so that's not a factor.

Bruce

Can you see the difference between 25m focus and infinity?  Yes, but you have to be good.  Very good.  Veryvery good.

Take some numbers: an eye is about 25mm in diameter = 0.025m.  So for a lens to focus on the retina, it needs to be a 40 diopter lens (diopters are the inverse of focal length in meters).

Thin lens equation says that 1/f=1/o +1/i.  An object at 25 meters will therefore have a focal point 24.96mm behind the lens.  That 0.04mm difference means that the blur line (circle of confusion) will be (25/25.04) -1 = 0.0016 of the aperture diameter wide.  Assume the aperture is 4mm, the circle of confusion will be 0.0064mm wide.

The retina at its most dense point has up to about 325,000 cells per mm2, based on 7 cadaver examinations, so .00175 mm between cells.  A circle of confusion 0.006mm wide means that 4 cones will see a shade of grey if something is not in 'perfect' focus.  Note that 'perfect' is at least 1 cell wide.  Cells are arranged in a roughly hexagonal pattern on the retina, any straight line, even in perfect focus, will sometines cover a cell at 100%, sometimes at 0%, but most often, somewhere in between.  So a 2 cell wide COF is the BEST your eye/brain can hope for before it detects blur.

Net, 'perfect' focus is a blur line 2 cell or less.  25mm focus is 4 cells of blur for someone with 20/15 vision.  Net, 25m focus is 'almost perfect', but only if you are 20/15 and pay VERY CLOSE attention.

Putting this in perspective, the blur we are talking between the lens options mentioned is in the dozens of pixels wide, so people who can distinguish between target distances and infinity are exceptionally gifted in vision resolution.

All of this is making my brain hurt…and now I can’t focus on the front sight!

My apologies, I think we went off course with my last couple of sentences of my post. I'd be happy to revisit this another time. The point I really wanted to make was out of the 7 illustrations of lens powers and f stops (pupil size), only 2 f stops were within the average shooters' pupils between the ages of 40 to 70 years old. All the others, I believe, will confuse beginning shooters with little sighting experience. When I see through a +1.00 or +1.25D add, I do not see the amount of blur shown in the 3 illustrations on the left. Pupils in the 1 mm range is not common so the 2 illustrations on the right have little value.

3/8"  =  9.525 mm
1/4"  =  6.35 mm
3/16"=  4.762 mm
1/8"  =  3.175 mm ****
3/32" = 2.381 mm  ****
1/16" = 1.588 mm
.045" = 1.143 mm

Norman

No apology necessary....just my feeble attempt at humor. It got very technical, very fast....brain overload! Lol.

I see that the illustrations on the right side represents views through apertures. This brings up an interesting side note to the topic of pupil sizes. Years ago, the eye drop Pilocarpine was popular for the treatment of glaucoma. Modern medicines have replaced Pilocarpine now. One of the side effects was small pupils among other unwanted other problems. The use of Pilocarpine has recently been revived with the FDA approved Vuity. The primary use of this eye drop is to "treat presbyopia" which allow one to see near without eyeglasses and without affecting distance vision. Are there any shooters out there using Vuity or know of any friends or relatives using it and care to comment?

Norman

Yes, I labeled my examples assuming the smallest human pupil was 1/8" = 3mm.  Thank you for your observations - I will update my labels to reflect your data that pupils can go as small as 3/32 or 2.5mm.  I will also drop the largest pupil sizes from the matrix.  These represent dilated pupils in dark conditions, and I initially included them to allow for indoor ranges with poor lighting.  However 1/4" is likely excessive as no one shoots in near darkness.

The smaller sizes represent apertures like EyePal or Merit Disks.  The extreme 0.045" represents the smallest apertures I see outdoor shooters using.

To Bruce:

Before my cataract surgery, I was highly nearsighted, with my shooting eye needing -10.00D. With my nearsighted prescription, I never experienced side peripheral distortion while using my past progressive lenses.  Now with my plano dist Rx with only the add in the lower progressive zone, I do note significant peripheral distortion to the point that I don't enjoy wearing them. You may or may not experience the same. If you go with bifocals, you can easily simulate the height of the bifocal by placing a piece of scotch tape onto the sample display lens of the frame. Get into your shooting stance and reposition the tape as needed until you get the perfect placement. A mm or two makes a difference. Do not bring your pistol for this unless the staff know in advance.

I would suggest that if you choose a new eyeglass frame, have the technician or doctor adjust the frame first before the scotch tape placement.

Norman H. Wong O.D.

Art, you are a gentleman and a scholar. As I had mentioned with a past post, the bullseye blur is not so problematic when using a center mass hold or sub-6 hold (or deep 6 hold). It does become more difficult while using a 6 O'clock hold.

Norman

The pictures look about right to me.  I have tried various solutions for irons and the .75 clip on top of my prescription glasses is the best I have found.  I absently minded left the clip on when switching to a pistol with a dot and found that it helped with focus.

My struggle with the .75 clip is in lower light (even outside under a roof), it is much easier to focus on the rear sight - very difficult to maintain a clear front sight (even with markings, paint, etc...).

If the +0.75 clip was meant for your front sight but also helped you see the red dot better, a couple of scenarios come to mind. 1. If this is consistent, your eyeglass Rx is not current  2. If this situation fluctuates, you may have unstable vision due to health issues or side effects from medications

ShootingSight’s apertures do something neat.  All of my dots are round (not starbursts or comets), and it’s easier to resolve aligned iron sights under the bull (the bull is less blurred and out of focus, which reduces the reflex to “look at” the bull.

All I'll add is that when I was competing my eyesight needed help as I aged. I ended up with Randolph Ranger shooting glasses with interchangeable lenses. I had lenses for iron sights and different ones for dot sights. They were a very good investment. If you can't see clearly, you can't shoot well. Opticians are usually very accommodating when you tell them what you need to do. As has already been stated, focus on the front sight with irons and either on the dot or target for an electronic red dot sight.