Prescription lenses for shooting glassea

[derekm]

Rob, up to you to decide the sphere value for a good foresight. If you don't have astig. or prism problems, try out some ready readers to get what will usually be a +ve value. If you have a negative prescription you'll have to estimate from the "near" or "reading" value. If you have astig. you'll have to estimate the sphere from the near value on your prescription. A pistol shooting lens will be weaker than reading, stronger than distance.

Until my astig. became noticeable (and before the Knobloch frames came along at a giveaway price!) I used a ready reader frame with a lens made by an internet Co. like reglaze.

[RobF]

Rob, up to you to decide the sphere value for a good foresight. If you don't have astig. or prism problems, try out some ready readers to get what will usually be a +ve value. If you have a negative prescription you'll have to estimate from the "near" or "reading" value. If you have astig. you'll have to estimate the sphere from the near value on your prescription. A pistol shooting lens will be weaker than reading, stronger than distance.

Until my astig. became noticeable (and before the Knobloch frames came along at a giveaway price!) I used a ready reader frame with a lens made by an internet Co. like reglaze.

Hi Derek,

Ah I get it, so the sphere is just the focal length adjustment on top of your prescription? ... so say my right eye is +1.25 to start with, then to focus at the foresight say at 1m, then I just add 1D. If it was at 2m away i'd add 1/2m = 0.5D If I want to focus at 0.5m then it would be 1/0.5m which is 2D.

Does that sound right?

I've got an astigmatism. Trouble is some opticians round the angle up to 5 degrees. Mine is actually 92... some write it as 95. But at least with shooting glasses you can fix it easily by rotating the lens.

[derekm]

Rob, you're getting near. The sphere is the main part of your prescription, the magnification if you like. Base your shooting estimation on the "near" or "near/reading addition" of the prescription and make your estimation from that.

My right eye sphere is +0.25 and the near addition is +2.25 (near sphere = +2.5). I ordered lenses to +1.0 and +1.25. with the astig cylinder as prescription. At the moment, the +1.0 is correct.

My last pair of lenses from 2 years back were +0.5 and +0.75. As my eyes degraded I went from the former to the latter.

Whatever your own figures, your shooting lenses will be less strong than your reading lenses and stronger than your distance.

Sorry if I can't put it into better words!

[RobF]

Rob, you're getting near. The sphere is the main part of your prescription, the magnification if you like. Base your shooting estimation on the "near" or "near/reading addition" of the prescription and make your estimation from that.

My right eye sphere is +0.25 and the near addition is +2.25 (near sphere = +2.5). I ordered lenses to +1.0 and +1.25. with the astig cylinder as prescription. At the moment, the +1.0 is correct.

My last pair of lenses from 2 years back were +0.5 and +0.75. As my eyes degraded I went from the former to the latter.

Whatever your own figures, your shooting lenses will be less strong than your reading lenses and stronger than your distance.

Sorry if I can't put it into better words!

No, that makes perfect sense thanks. I never quite twigged the near sphere just altered the distance. That makes sense.

[derekm]

The sphere is the degree of magnification, whether near or distance. Less is required for distance focussing, more for reading and somewhere between for pistol, desktop computer etc..

If you have astigmatism, your eyes produce a "squerged" image, (a square becomes a parallelogram), but for mild cases, the brain corrects this. The cylinder, tilted at an angle, feeds a corrected image to the brain and this correction is the same for both close-up or distance. When you first get astig. corrected glasses, because they over-ride your brain, you tend initially to get a squerged image and may, like me, take the glasses back saying they are wrong! After a couple of days, your brain re-adjusts to the now correct image it is receiving.

Prism, I do not really understand, but I think it is correction for cross-eyes.

[vbull]

So, for shooting purposes what difference does it make where the datum is, whether at 9 or 12 o'clock ?

[Sir_SwampThing]

So, for shooting purposes what difference does it make where the datum is, whether at 9 or 12 o'clock ?

I image that the rotation of the lens affects the amount of correction? If the lens is mounted with the datum point in the wrong position, it would possibly increase the astigmatism instead of correcting it?
Or am I way off?

Cheers
Chris

[derekm]

So, for shooting purposes what difference does it make where the datum is, whether at 9 or 12 o'clock ?

It doesn't per se. Nothing to do with shooting purposes, it is aligning the cylindrical form built into the lens to your eye. The datum, reference point or whatever you want to call it lets you turn the lens to the correct position. If the lens maker puts the mark at 9 o'clock, you put it in the frame at 9. 12 o'clock, install at 12.

If you already have glasses with astig. correction, look through one lens and rotate the glasses. The image will become distorted and the penny will drop.

[RobF]

The sphere is the degree of magnification, whether near or distance. Less is required for distance focussing, more for reading and somewhere between for pistol, desktop computer etc..

If you have astigmatism, your eyes produce a "squerged" image, (a square becomes a parallelogram), but for mild cases, the brain corrects this. The cylinder, tilted at an angle, feeds a corrected image to the brain and this correction is the same for both close-up or distance. When you first get astig. corrected glasses, because they over-ride your brain, you tend initially to get a squerged image and may, like me, take the glasses back saying they are wrong! After a couple of days, your brain re-adjusts to the now correct image it is receiving.

Prism, I do not really understand, but I think it is correction for cross-eyes.

Got it.

I've got astigmatisms in both eyes.

[derekm]

Me too, mild in the left and more pronounced in the right.

Just fitted one of the new lenses yesterday and have a marked improvement in my shooting already.
The sight image with the two year old prescription was good, I thought! How wrong!!

A few years back I had a PB of 94 and averaged 87.5 over 100 rounds. This deteriorated with my eyes until I was hard pushed to score an 80!
Hopefully I'm now on the road to improvement after a couple of 87s last night!

At only £15 a pair, it's worth trying a few strengths of lens.