TargetTalk

I can make them.

I sell clip-on lenses at Camp Perry, but had never put them on my website, so I'll get that fixed in the next days. Cost is $55. I normally make +0.50 and +0.75, but can make a +0.25 as well.

www.shootingsight.com

i was today at the eye doctor. she made me understand that there are 2 kinds of "diopters". spherical deformation and cylindrical deformation
i have +0.25 on sph and -0.50 on cyl (ax 99).

so the +0.50 or +0.75 that is talked about in this thread is applied to the spherical deformation number. the cylindrical deformation is the same no matter if it;s close reading glasses (+) or distance glasses (-)

i tested with different lenses and the best was +0.75 sph , -0.50 cyl

so the +0.50 or +0.75 that is talked about in this thread is applied to the spherical deformation number

Yes

Cylinder is the amount of astigmatism and is the same for distance and near.

got now the lens in the glasses...and i cannot see anything. the front sight is REALLY blurry :(
could it be that it's installed incorrectly in the glasses?

Is the lens round? If so, you may need to rotate it, because of the cylinder.
ShootingSight sent me instructions when they made me a lens for my Varga frames (BTW, if you have the prescription I STRONGLY suggest their services, no idea if they can work internationally though)

gimgim wrote: ↑Tue Sep 03, 2019 5:35 pm Is the lens round? If so, you may need to rotate it, because of the cylinder.
ShootingSight sent me instructions when they made me a lens for my Varga frames (BTW, if you have the prescription I STRONGLY suggest their services, no idea if they can work internationally though)

the lens is rounds. and the ax for the cylinder is marked. it is in the correct position..
but anyway, i rotated and it;s almost the same in any position. i don;t think the blurriness comes from the cylinder

i don;t think remote optometrist would work in the case. i need troubleshooting... :)

I'd take it back or to a local optometrist and ask them to measure the lens. Sometimes they don't set the grinder up right, and things can be way off. There can also be some confusion with the way the axis is specified for astigmatism between doctors & the lens folks. I had a bunch of lenses that were off by exactly 90 degrees, so a little rotation might not have been enough.

Several things:

1. Yes, I work internationally.
2. Greg nailed it. A lens with a cylinder correction needs to be oriented.
3. I forget the history, but eye doctors and opticians operate using different units of measure. One uses positive cylinder values, the other uses negatives. The cylinder value is an incremental value, because the lens has one diopter in one direction, and another diopter in another. So prescriptions in one case are written with the sphere being the lesser of the two, and the cylinder being a positive number that is added to get the other. The other system gives the highest value for the sphere, and has a negative cylinder value that is subtracted. Both do the same thing, but it is easy to get them confused or forget to do the conversion from one to the other, so you end up with a wrong lens.

Net, a lens that is +1 diopter in one axis, and +2 in the other could be notated as +1 Sphere, +1 Cylinder, or +2 Sphere, -1 cylinder.

In your case, the +0.25S, -0.50C that is your prescription means that your lens is +0.25 in one direction, and -0.25 in the other, so the +0.25S, -0.50C could also be written as -0.25S, +0.50C.

Per what others recommended, take the lens to an optician, and ask them to measure it. It sounds like someone just made the wrong lens.

Gwhite wrote: ↑Wed Sep 04, 2019 7:52 am I'd take it back or to a local optometrist and ask them to measure the lens. Sometimes they don't set the grinder up right, and things can be way off. There can also be some confusion with the way the axis is specified for astigmatism between doctors & the lens folks. I had a bunch of lenses that were off by exactly 90 degrees, so a little rotation might not have been enough.

you were right!
i went back to the eye doctor and the lens was rotated 90 degrees. very weird. the lens folks used what looked to me the exact same device, but the results were different.
now it;s ok. front sight clear, bullseye blurry

If lens is round, just be careful with the astigmatisms angle marker.

0 degree is at 3 o’clock facing you, not at the 12 o’clock position

So make sure your marker at lens edge line up at 3 o’clock position.

Lenses do not come with a 0 axis mark from the factory, if for no other reason than that '0' for someone measuring using a '+ cylinder' instrument will be 90 degrees offset for someone using a '- cylinder' instrument. Further, lenses are made in a big diameter, about 3" across, and cut down to the size and shape needed for the frames, so any mark on the edge would be cut away.

Any markings for astigmatism orientation are added by the lens lab after the cut, and are usually put at 12 o'clock for the patient. The exception, obviously is if someone misread the prescription, as seems to have happened here, so the correct lens power was produced, but the lens was misoriented by 90 degrees in the lensometer, so the 12 o'clock mark accidentally ended up at 3 o'clock.

Why the optical industry cannot come together and agree on a common terminology for lenses is beyond me. The math to convert from one notation to the other is noit difficult, but it does lead to errors when misread.