Little notch on the edge of the lens in my Champion Olympic frames.

[Sir_SwampThing]

I had my eyes tested and my prescription (it turns out) includes correction for slight astigmatism. The optician never mentioned this at the time.
When the lens holder was returned with the lens fitted, I just collected it and went home. Only then did I realize that the lens was in backwards, so I just loosened the screw and flipped the lens over.
For three weeks now my shooting has been awful. I have centred and recentered the lens, tweaked this that and the other, with my adjustable iris and without but no improvement. My focus on the front sight is spot on, with the iris it brings the rear sight clearer and the target is improved but I began to notice that the black of the target had a ghost to the left, about half width again. If if moved my eye (not my head) ever so slightly to the right the ghost disappeared but I guess this was introducing parallax error plus it was uncomfortable. This got me into thinking about astigmatism and when I read my prescription, there it was +1.50/-0.25/10.
I remember reading something about the notch on the lens being there to indicate the correct rotation of the lens in the holder to achieve the correct axis for correction but I cannot find it online now. I am of a mind that I have rotated the lens when I reversed it (effectively increasing my astigmatism) but now I don't know where the notch should be. I have spoken with the optician and they have not got a clue, I tried to speak to the glazing department but they refused to give me any advice/info, all they did was ring the optician and give them a rollicking for giving me their number!
After my ramble, can the collective help, please?
Is there any standard/norm? I am guessing that the notch should be either 12/3/6/9 o'clock?
Thanks in advance.

Atb
Chris

[thirdwheel]

Simple really, put some news print on the wall and sit the correct distance from it to get it in focus and then rotate the lens in your fingers until you get the best picture and the least distortion. Then have a look at where the notch is and use that to help you put it in the holder, my guess the notch is at the zero meridian to allow the optician put it in the frame at the correct angle but the way to do it above works too and you will be surprised how often lenses get put in glasses incorrectly at the slightly wrong angle. You may even be able to rotate the lens while it is in the holder which makes it even simpler to do. If you cannot suss out the best place using print draw some circles and use them and when they are the roundest and not distorted you have found your point.

On another note regarding your iris and the use of it, don't use it to help you focus and increase the depth of field eg. bringing the target, front sight and back sight into focus, you are better without it at all, you really do not want to see the target that should be a fuzzy blob, the back sight should just be out of focus and you should be able to see the molecular structure of the front sight as clear as day. Why do some people use them? at different ranges there are different ambient light levels and they use them to get a controlled amount of light going into their eye and not to help focus, the aperture used is large, leave it in the box, your balance will be better too.

[silvershooter]

Hi Chris

If your astigmatism is only -0.25, they will not have put that prescription in the lens as it is considered too small, an error in the manufacture could be more than that.

This is an article about contact lenses but it applies

https://www.quora.com/Are-there-cont...25-astigmatism

Dave

[RobinC]

Thirdwheel is spot on, and his set up technique is the best way to be sure its correct, usually the notch or mark is on 12 o'clock, but that can be out a tad.

I also agree on iris's, old tech that people cling to, they just mess up the focus, draw the focus to the aiming mark, and reduce light, and the more light on the eye the better. Get the non aiming eye blinder as small as possible, just enough to blank the sight picture and no more, also to gather as much light as possible, and have it in a translucent material.

Have Fun
Robin

[thirdwheel]

On hard lenses used for glasses 0.25 cyl is available but the correction is only minor, if the lab could not work to way under a tolerance of 0.25 cyl on hard lenses they would go bust very quickly. I do have issues with lens accuracy and that is why I bought a Lensometer to test the lenses I get, here is why - Opticians rely on you moving your head to get stuff in focus when reading etc. or allowing for some accommodation you may still have, and we do it without thinking when reading and the nearer you get towards your nose the shorter the sweet spot is (depth of focus). Here lies the problem, holding out a pistol at arms length and looking at the front sight it is a complete no no to move your head backwards and forwards to get the focus of the front sight correct, and if you are going to start forcing the focus with your eyes you are going to tire quickly in a match. The lens has to be perfect match to your requirements and the rule of thumb of + 75 D from the distance prescription may be ok for some but it does not suit everyone. I've short arms and the rule of thumb does not work for me if the lens is worked out mathematically. Now chuck into the mix the tolerance the lens makers work to (they are usually very good) and your shooting lens may just be not good enough. After having a run of lenses that did not seem to work I bought the Lensometer to measure what I had and found them all just a tad out, and one set at the wrong Axis but easy to put right. I also then learnt how to refract and bought a set of test lenses to get my lens prescription perfect. If you look up the writings on shooting vision of Don Nygould the ex world champion and long time member of the American Olympic Squad all will become clear.

Looking at the prescription above there is no way of telling if that is the distance prescription or the prescription for the shooting lens but my guess it is the distance prescription but there is a puzzle with the maths which I will not go into here but involves the Add D you need to put on the sph lens for the amount of minus Cyl prescribed.

The only way to get a correct lens is to take your pistol to the opticians and turn all of the lights on, point at a white wall, use a translucent blinder to let your Iris work correctly, relax your eyes and use the old fashioned trial frame and lenses and not a Phoropter. Getting an optician to do this may be the biggest problem.

[silvershooter]

Well, I am also Cyl -0.25, in my L eye. I have prescription reading glasses, I rotated the lens through 180 deg,it did not make any difference to visual acuity in my L eye.
My R eye is Cyl -1.00, it did make a big difference rotating the lens through 180 deg.
My optician has definitely ignored the -0.25 astigmatism in my L eye. I will ask about this next time I go in.

[RobinC]

I was always told 0.1 dioptre was the tolerance on hard lenses.

The correct eye sight correction is critical in all target shooting, rifle and pistol, if you can't see properly, you can't shoot properly

Have Fun
Robin

[Sir_SwampThing]

Thank you all.
The lens is definitely +1.5/-0.25, two other opticians have measured it now and confirmed it.
Tonight I intend to re-centre and begin tweaking the rotation until the problem is solved (hopefully).

Cheers
Chris

[BigEars]

When i had my lens made, the optician asked where i wanted the orientation Mark. Did yours not mention this?

[Sir_SwampThing]

When i had my lens made, the optician asked where i wanted the orientation Mark. Did yours not mention this?

No, nothing at all. And when I subsequently enquired as to where the notch should be, I may aswell have been speaking double Dutch.

Atb
Chris