Shooting Glasses Monocle Concave?

Oz · Post by Oz » Thu Mar 26, 2009 6:42 pm

I bought a set of Varga shooting glasses from Pilkguns and then went to my sports focused opthamologist. It turns out that my ideal shooting lens is merely -.25 less than my regular prescription. Young enough eyes for now I guess... I got a new set of regular glasses and the monocle for the Varga glasses.

They all came in today. The regular glasses fit and feel great. I put the monocle in and WHOAH! Something is waaay wrong. I can't focus on anything. It felt a bit like I was looking through my glasses backwards. Wait... hold it...

So I flip the monocle around so that the concave surface faces out (rather than what I expected, convex facing out). Voila, I see fine with the monocle.

That doesn't sound right to me. Anyone else shooting with their monocle concave side out?

Oz

David Levene · Post by **David Levene** » Fri Mar 27, 2009 2:16 am

Two questions:-

1) How strong is the lens

2) How far is it away from the eye compared to your regular glasses

Once you start getting to around -6.0 the distance from the eye becomes mor critical.

bruce · Post by **bruce** » Fri Mar 27, 2009 2:22 am

I have seen at least one person shoot with a lens, where the concave surface is away from the eye.

tleddy · Post by **tleddy** » Fri Mar 27, 2009 9:30 am

Having a negative lens from your 20/20 distance Rx for sighting is VERY unusual.

In virtually all cases, one needs help to focus on a nearer object such as the front sight. That requires a + diopter lens.

Questions:

What is your age?

What is the Rx for your distance vision

If you have bifocals to read, what is the Rx for that

What pistol(s) are you shooting and what is the distance from your eye to the front sight on each

Let me know and I can give you my Quack opinion...

Tillman,
Creator of the ClearsighT Optical Sighting Device

David Levene · Post by **David Levene** » Fri Mar 27, 2009 11:05 am

tleddy wrote:Having a negative lens from your 20/20 distance Rx for sighting is VERY unusual.

Oz actually said "-.25 less than my regular prescription". To my mind, that's +0.25 on his regular prescription, which is what you would expect.

Oz · Post by Oz » Fri Mar 27, 2009 12:32 pm

Well, I'll back up and start with the basics.

I'm 37, shooting an LP10. I went in for a standard eye exam to get a new set of glasses. The results for my new glasses:

R | -3.75 SPH | +.75 CYL | 62 Axis
L | -3.75 SPH | +1.00 CYL | 75 Axis

I use my right eye when I shoot.

We next measured my front sight distance. 1.4+ meters as I recall (long arms). My doctor held some fine print at the appropriate distance. Since he was too far away to adjust lenses, he had me adjust the rings and roll it down until the text was the sharpest and darkest (held at the front sight distance). We started from my new prescription.

1 click down was slightly better, 2 clicks it started to go softer. After doing this for a few minutes, taking as much as 5 clicks each direction, 1 click down was the best. He stated that this is exactly what he expected from my 'younger' eyes. He told me that he needs 11 clicks just as an example of older eyes.

With that, the prescription for my shooting lens was:
R | -3.50 SPH | +.75 CYL | 62 Axis

When I put the lens in my Varga shooting glasses, instinctively I put the lens in convex towards the target. It was fuzzy at all distances and made my eye water. On a hunch, I flipped the lens; concave towards the target and the front sight became clean and crisp. The target is ever so slightly less crisp (compared to my new standard glasses), which is okay since I have a bad habit of which I believe you can all guess.

I'm not sure that this is a question so much as just reaffirming that yes, the lens should be set with the concave surface facing the target. From some of the other posts here, it appears that the concave surface facing the target is not unheard of.

Otherwise, there are likely bigger issues at play :)

Oz

David Levene · Post by **David Levene** » Fri Mar 27, 2009 12:59 pm

Oz wrote:I'm not sure that this is a question so much as just reaffirming that yes, the lens should be set with the concave surface facing the target. From some of the other posts here, it appears that the concave surface facing the target is not unheard of.

No, it's not unheard of.

It might be interesting to get someone to try and measure the distance from your eye to the nearest surface of the lens with:-
1) Your normal glasses
2) Your Vargas with the concave surface facing you
3) Your Vargas with the concave surface away from you

If there is a difference between 1 & 2 and a smaller difference between 1 & 3 then that could be your problem.

OzzieM · Post by **OzzieM** » Fri Mar 27, 2009 2:53 pm

We next measured my front sight distance. 1.4+ meters as I recall (long arms).

Hmmm...either you are a knuckle dragger, or your recollection is faulty, or this is a typo, or this may be the explanation: Eye to front sight distance was more likely 1.04 m, rather than 1.40 m. I am 6'-4" tall with long arms, my viewing distance is approximately 1.02 m (I also shoot an LP10). If this kind of mistake was made when you got your prescription, perhaps that explains your problem.

OzzieM

tleddy · Post by **tleddy** » Fri Mar 27, 2009 3:05 pm

Mr. Levene interpreted the measurement correctly - I did not.

That being said, a 1/4 diopter net plus is a very minor correction, but should be of some help.

In my experience, the manufacturing tolerance on regular lenses can easily be +/- 0.125 diopters. Did the optometrist confirm the prescription on the measurement device to confirm Rx?

I will also note that competition shooters are some of the few people that can discriminate a 0.25 diopter difference.

OzzieM makes a good point also, unless you have a huge extension on the front sight :-)

Tillman

tleddy · Post by **tleddy** » Fri Mar 27, 2009 3:11 pm

One more thing... you have an astigmatic correction in the lens.

Depending on the way things are marked, you must have the vertical axis of the lens properly aligned. Hopefully there is a mark on the lens that is at 12:00 noon - that should be at 12:00 noon in the frames as well - otherwise you will have distortion due to the axis being off the 62 axis.

Please let me know how the lens is marked.

Tillman

David Levene · Post by **David Levene** » Fri Mar 27, 2009 4:38 pm

tleddy wrote:I will also note that competition shooters are some of the few people that can discriminate a 0.25 diopter difference.

I went to a new optician last year for normal glasses. In his instructions to the lens makers he made special note that I am a pistol shooter so the lenses had to be spot on. He'd had trouble with shooters before.

David Levene · Post by **David Levene** » Fri Mar 27, 2009 4:44 pm

tleddy wrote:Depending on the way things are marked, you must have the vertical axis of the lens properly aligned. Hopefully there is a mark on the lens that is at 12:00 noon - that should be at 12:00 noon in the frames as well - otherwise you will have distortion due to the axis being off the 62 axis.

I admit that I am no expert on lenses, which is probably why I am confused.

If you pivot the lens around the vertical axis, doesn't that throw the astigmatism correction angle the wrong way.

tleddy · Post by **tleddy** » Fri Mar 27, 2009 5:21 pm

David-

You are correct... the lens must be in the proper orientation in the frame. Rotation of the lens off axis will result in distortion.

That is why I inquired about the markings. Some makers put the orientation mark at the top; for some reason, others put marks at the 90 and 270 degree points on the lens.

One of the puzzles in my mind concerns the orientation of the convex vs. concave position. If the 62 axis is properly oriented, I am fairly certain that the convex surface should be towards the sights.

If the axis is rotated on the vertical center the correction axis is off by 180 degrees and the vision will be blurred... essentially doubling the astigmatism.

Tillman

David Levene · Post by **David Levene** » Sat Mar 28, 2009 4:37 am

tleddy wrote: You are correct... the lens must be in the proper orientation in the frame. Rotation of the lens off axis will result in distortion.

Maybe I didn't explain myself properly Tillman, or more likely did not understand your answer.

My point was, if you reverse the concave and convex surfaces while leaving the top of the lens still at the top, doesn't the 62 degree astigmatism correction angle become 118 degree.

tleddy · Post by **tleddy** » Sat Mar 28, 2009 9:17 am

David-

We are saying the same thing in different ways... I do not know how to convert the 62 to the other degree based on rotation of the lens and get the number of degrees.

It would seem to me that you are correct - the 0 to 180 for the cylinder is mirrored on the rotation, so 180 - 62 would give 118 degrees.

We certainly agree that if the lens were improperly mounted, the distortion would be exaggerated.

Tillman in Florida

FredB · Post by **FredB** » Sat Mar 28, 2009 5:12 pm

IIRC, the Cylinder correction on lenses is symmetrical, i.e. a correction of a certain amount at X degrees will be identical at X+180 degrees. If that's the case, then rotating the lens on its vertical axis as was described would not alter the Cylinder correction (as long as the rotational orientation of the lens stayed the same).

Just a guess, but I suspect that Oz, purely by chance had the rotational orientation off by around 90 degrees when he had the concave side facing his eye, and again by chance got the rotation closer to the correct angle when he turned the lens around. Normally the concave side should face the eye.

I have found that, even when the lens is left unmarked for its correct position regarding Cylinder correction, it's not that difficult to try rotating it 5 or 10 degrees at a time to different orientations until you find the "sweet spot". I'd suggest that Oz place the concave side facing his eye, and rotate the lens until the image is optimal. If the lens does have a notch or other mark on it, I would try placing it at 0 and 90 degrees to see which is better.

HTH,
FredB

David Levene · Post by **David Levene** » Sun Mar 29, 2009 3:40 am

FredB wrote:IIRC, the Cylinder correction on lenses is symmetrical, i.e. a correction of a certain amount at X degrees will be identical at X+180 degrees. If that's the case, then rotating the lens on its vertical axis as was described would not alter the Cylinder correction (as long as the rotational orientation of the lens stayed the same).

I don't agree Fred.

As an example, consider a lens with cylindrical correction at 62 degrees clockwise from vertical. If you then rotate the lens around its verticle axis, i.e. swap the concave and convex faces while leaving the top of the lens at the top, the cylindrical correction will then be 62 degrees counter-clockwise from vertical. That is the same as 298 degrees clockwise from vertical and, as you say with a symmetrical axis, that is the same as 118 degrees clockwise from vertical. The cylindrical correction will therefore be 56 degrees out.

tenex · Post by **tenex** » Sun Mar 29, 2009 9:17 am

Hi Oz,
Very simple science project. Take the lens holder out of your glasses and just hold the lens over your eye and look at the same newspaper. Now rotate the lens and see what happens. I'm sure you'll find that you can find an orientation that works great with the lens either concave side in or out. It just won't be the same orientation.

I think if you brought everything to your eye doctor he'd have you straightened out in about 5 minutes.

Steve.

P.S. I don't know how they mark the axis correction on a round lens, but they must do something. Your lens is just rotated to the wrong angle (or your eye doctor wants you to use the lens concave side out, I'd ask).

FredB · Post by **FredB** » Sun Mar 29, 2009 11:26 am

David Levene wrote:
FredB wrote:IIRC, the Cylinder correction on lenses is symmetrical, i.e. a correction of a certain amount at X degrees will be identical at X+180 degrees. If that's the case, then rotating the lens on its vertical axis as was described would not alter the Cylinder correction (as long as the rotational orientation of the lens stayed the same).
I don't agree Fred.

As an example, consider a lens with cylindrical correction at 62 degrees clockwise from vertical. If you then rotate the lens around its verticle axis, i.e. swap the concave and convex faces while leaving the top of the lens at the top, the cylindrical correction will then be 62 degrees counter-clockwise from vertical. That is the same as 298 degrees clockwise from vertical and, as you say with a symmetrical axis, that is the same as 118 degrees clockwise from vertical. The cylindrical correction will therefore be 56 degrees out.

David,

As soon as I visualized what you described, I realized that you are absolutely correct (except for the unlikely case when the cylinder correction happens to be exactly at 90 degrees at the start). A bit of sloppy thinking on my part! Still, I think the remainder of what I said is correct?

FredB

Oz · Post by Oz » Mon Mar 30, 2009 12:54 am

I very much appreciate everyone's input. I spent about 20 minutes staring at a target, holding my monocle in my hand and spinning it around.

Sure enough! The lens is almost exactly 45 degrees off axis. If I put the lens convex towards target (as I assumed it should have been in the beginning) as mounted, it is awful. During my tests the image magically clears up and is actually QUITE sharp and pleasant at 45 degrees rotation.

Apparently when I flipped the lens over (concave towards target) it put the off axis astigmatism in a position that was simply more tolerable.

As the lens is mounted, I see no marks. But it's pretty obvious where the correct position is and I would probably spin in myself. I'm just not sure how forgiving the 'roundness' (or lack thereof from this monocle) will be in clamping on the lens in a different position. I will soon find out!

Thanks again everyone!

Oz

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