Lens Identification

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TomF
Posts: 156
Joined: Mon Mar 01, 2004 9:41 am

Lens Identification

Post by TomF »

I am getting older and my the lens that I have are not strong enough.

I have a pair of Varga 2000 and one lens has two dots and the other has three dots. I cant remember what those magnifications are, .25 and .50 or .50 and .75?

Whatever they are I need a stronger lens.

Anyone know what the dots represent on the lens?

Thanks!
Rover
Posts: 7055
Joined: Sat Nov 15, 2008 4:20 pm
Location: Idaho panhandle

Post by Rover »

Get yourself a presciption from your eye doctor with the extra power built in. It will also have corrections for other problems you may have, such as astigmatism.

Do a search and you'll find many of your questions answered, but not always correctly. (That's right; if it's on the Net it must be true!)

BTW I think you have a .50 and .75.
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conradin
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Location: Basement.

Post by conradin »

My Knobloch has dots on the lens, and they help me to align the lens correctly to the frame.
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RobStubbs
Posts: 3183
Joined: Mon Mar 01, 2004 1:06 pm
Location: Herts, England, UK

Re: Lens Identification

Post by RobStubbs »

TomF wrote:I am getting older and my the lens that I have are not strong enough.

I have a pair of Varga 2000 and one lens has two dots and the other has three dots. I cant remember what those magnifications are, .25 and .50 or .50 and .75?

Whatever they are I need a stronger lens.

Anyone know what the dots represent on the lens?

Thanks!
Surely it doesn't matter what they are if none of them are right for you ??

Get yourself to an optician/optometrist and get the correct ones made up, and ask for a copy of the prescription.

Rob.
TomF
Posts: 156
Joined: Mon Mar 01, 2004 9:41 am

Re: Lens Identification

Post by TomF »

RobStubbs wrote:
TomF wrote:I am getting older and my the lens that I have are not strong enough.

I have a pair of Varga 2000 and one lens has two dots and the other has three dots. I cant remember what those magnifications are, .25 and .50 or .50 and .75?

Whatever they are I need a stronger lens.

Anyone know what the dots represent on the lens?

Thanks!
Surely it doesn't matter what they are if none of them are right for you ??

Get yourself to an optician/optometrist and get the correct ones made up, and ask for a copy of the prescription.

Rob.
Surely it does matter what they are. Since I dont need them anymore, when I sell them I want to be able to give a proper description.

I am going with regular glasses, left lens normal bifocal prescription and right lens with bifocal top focus on front sight and bottom reading distance so I can see downrange, my front sight, and see the gun to make adjustments. I also use an occluder to shoot with. So I got it all covered.
Rover
Posts: 7055
Joined: Sat Nov 15, 2008 4:20 pm
Location: Idaho panhandle

Post by Rover »

Big mistake! You will have a mess on your hands.

Get one lens with your scrip plus the correction to pull the focus of your eye to the front sight. I'm assuming you have shooting glasses such as Knobloch or Champion, since you have the single lenses.

Your optometrist will tell the power of the lenses you have (for free).
TomF
Posts: 156
Joined: Mon Mar 01, 2004 9:41 am

Post by TomF »

Rover wrote:Big mistake! You will have a mess on your hands.

Get one lens with your scrip plus the correction to pull the focus of your eye to the front sight. I'm assuming you have shooting glasses such as Knobloch or Champion, since you have the single lenses.

Your optometrist will tell the power of the lenses you have (for free).
Big wrong! But thanks for your opinion.
Rover
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Joined: Sat Nov 15, 2008 4:20 pm
Location: Idaho panhandle

Post by Rover »

If you know the answer, why ask the question?
TomF
Posts: 156
Joined: Mon Mar 01, 2004 9:41 am

Post by TomF »

Rover wrote:If you know the answer, why ask the question?
"Since I dont need them anymore, when I sell them I want to be able to give a proper description."
Rover
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Post by Rover »

Rover wrote: Your optometrist will tell the power of the lenses you have (for free).
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ShootingSight
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Post by ShootingSight »

I recommend you don't mess with inverted bifocals to try and sight through.

THe correct answer is that if you do not want a bifocal to focus on the front sight, as such a close focus will excessively blur the target. If you go through the photographic math to calculate hyperfocal distances, and do the accompanying math to calculate lens strength (which is what I did), or if you dig through this forum to find threads from people who have determined what power worked for them, you will see that the correct answer is that you need to take your distance prescription, and add either +0.5 diopters if you are shooting a rifle, or add +0.75 diopters if you are shooting a carbine/AR or pistol.

Those two powers will locate your focal point so your eye's depth of field is centered between the target and the front sight, with the front sight being as close to the near edge of your depth of field as your target is to the far edge of your depth of field. In this condition, the total blur that your eye sees on either the front sight or the target is at a minimum. If you go up or down in power, you will gain on one or the other focus, but give up more on one than you gain on the other.

That is the lens you want to look through to shoot, and the distance you are focusing at is called the hyperfocal distance. You can google that term, and find lots of photography sights that explain it in more detail, but basically, if I want to focus a camera so a near subject is in focus, and the background is in focus as well, the correct focal point is the hyperfocal distance.

In addition, I agree with your notion of getting an ADD of about +2.00 diopters so you can see up close to adjust the sights. Note that an ADD of +2.00 will be very strong (focus at about 16"), because 'ADD' for bifocals is a delta value relative to the distance power, and since you already augmented the distance power slightly to get the the hyperfocal distance, a +2.00ADD is strong. However, for rifle, I like this, because if shooting prone, and you are slung in, the sights are closer than reading distance.

As to seeing downrange, the top of your left lens should be good for that.

BTW, this will be strange to the eye doc, but if you augment the right lens for shooting by eg +0.50, and have an ADD bifocal of +2.00 (ie 2.5 total power in the right bifocal), you will want to have an ADD bifocal of +2.50 in the left eye, so both eyes are seeing the same power when you look through the bifocals. Normally, ADD is the same for both eyes, so you'll need to explain to your eye doc that the right eye already has an add built in to the distance lens.
TomF
Posts: 156
Joined: Mon Mar 01, 2004 9:41 am

Post by TomF »

ShootingSight wrote:I recommend you don't mess with inverted bifocals to try and sight through.

THe correct answer is that if you do not want a bifocal to focus on the front sight, as such a close focus will excessively blur the target. If you go through the photographic math to calculate hyperfocal distances, and do the accompanying math to calculate lens strength (which is what I did), or if you dig through this forum to find threads from people who have determined what power worked for them, you will see that the correct answer is that you need to take your distance prescription, and add either +0.5 diopters if you are shooting a rifle, or add +0.75 diopters if you are shooting a carbine/AR or pistol.

Those two powers will locate your focal point so your eye's depth of field is centered between the target and the front sight, with the front sight being as close to the near edge of your depth of field as your target is to the far edge of your depth of field. In this condition, the total blur that your eye sees on either the front sight or the target is at a minimum. If you go up or down in power, you will gain on one or the other focus, but give up more on one than you gain on the other.

That is the lens you want to look through to shoot, and the distance you are focusing at is called the hyperfocal distance. You can google that term, and find lots of photography sights that explain it in more detail, but basically, if I want to focus a camera so a near subject is in focus, and the background is in focus as well, the correct focal point is the hyperfocal distance.

In addition, I agree with your notion of getting an ADD of about +2.00 diopters so you can see up close to adjust the sights. Note that an ADD of +2.00 will be very strong (focus at about 16"), because 'ADD' for bifocals is a delta value relative to the distance power, and since you already augmented the distance power slightly to get the the hyperfocal distance, a +2.00ADD is strong. However, for rifle, I like this, because if shooting prone, and you are slung in, the sights are closer than reading distance.

As to seeing downrange, the top of your left lens should be good for that.

BTW, this will be strange to the eye doc, but if you augment the right lens for shooting by eg +0.50, and have an ADD bifocal of +2.00 (ie 2.5 total power in the right bifocal), you will want to have an ADD bifocal of +2.50 in the left eye, so both eyes are seeing the same power when you look through the bifocals. Normally, ADD is the same for both eyes, so you'll need to explain to your eye doc that the right eye already has an add built in to the distance lens.
Sorry to muddy the waters.

I didnt even read more than your first paragraph. But I am not inverting a bifocal.

I have computer glasses with my prescription adjusted to -2.5 for seeing the computer screen, and the bifocal -1.75 for reading. The -2.5 is the correct prescription for focusing on the front sight exactly 34" from my eye. If I only had a lens of -2.5 in the Varga frame, I would not be able to see anything that is more or less than 34" in front of me. So to see close, I have the bifocal (lower part of the lens) at my normal bifocal strength of -1.75.

Now that takes care of the aiming eye, my right eye. On the left eye I have my regular prescription bifocal lens so I can see up close with both eyes, and I can see farther than 34" without having to change glasses. And I use an occluder to cover the left eye when shooting.

I have many pair of both regular bifocal and computer glasses all with the same frames. SO, I just took the right lens out of my computer glasses and placed it in one of my regular glasses.

So I am going to sell my Varga frames and two lenses, one with three dots and one with two dots. And if you go to the top, all I asked was what power is indicated by the two and three dots on the lenses.

I'm done. Got my answer, thank you. Dont care about the rest. Good bye!
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