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Base Curve Definition

Yes, curved lenses, same curve on front and back .... Or flat lenses with same curve on front and back are called plano lenses.

So all "non RX" lenses, without power are considered plano lenses. This is widely accepted industry standard.

In glasses a "plano-convex" lens would be called a "plus" lens. This magnifiers and has plus power... The plus power would be measured in diopters. So if front curve is 8.75 D, and back is flat (0 D). The total power of that "Plano convex" lens is +8.75 sphere.

It would have a focal length = 1/D of only 11 cm, or about 4.5 inches. I hope that helps....

OK, but then the "industry standard" deviate from the optics definition used in other places where "plano" means that the lens has (one) flat surface. I'm not testing you, just curious why/if glasses use different nomenclature than photo optics, which wouldn't be too surprising.

A miniscus lens, without power, per your definition is a plano lens. Not "Plano" curved, but "Plano" power. See Plano curve means 0 base curve. Plano power means the front and back surfaced are parallel.

No, not per my definition! 😂 I'd call it a meniscus when both surfaces are facing the same way and none of them are plane. ;)

Never heard of "plano power", but I'm sure you know that better than me. 😊
 
No problem,

You are right. Radius of curve (contact lenses) basically makes a flatter lens a larger base curve i.e. 8.8 mm, and a more curved contact lens would have a smaller radius, so like 8.4mm.

On glasses/lenses the base curve isn't based on a unit of radius at all (though they are too big really to use mm anyway, maybe cm would have worked)! You are correct. It's confusing when you don't know where to find answers.. Thank goodness for the forum.

The base curve of glasses is based on diopters... Diopters are the same units used to measure RX power. Aka Sphere or cylinder power on your Eye Doctors script.

1 diopter is equal to the amount of a curve/thickness of lens that refracts (bends light) parallel light rays to a focal point at 1 meter.

F (focal length in meters) = 1 / Diopters

An example in a lens that was a +8.00 base curve on front, and a +0.00 base curve on back, would be a +8.00 sphere diopter lens. This lens would have a focal length of .125 meters, or 12.5 centimeters, or about 5 inches.

Because F (m) = 1 / 8 (D)

Long story short is that's about how curved many Oakley lenses are, 8.75 D. But both the front, and backside are 8.75D. front and back of lens are parallel, and have no power, hence the term "plano" lenses which means "level" or "flat"... A flat lens is technically 0.00 D on front, and 0.00 D on back.

Does this help?

Your brain 🧠 is a big brain.
 
@Chris A Hardaway. A little plausibility check for me to see if I am on the right track :
2560px-Lens1b.svg.png

Figure 1:CC BY-SA 3.0: Lens - Wikipedia

Lens maker's forumula: diopters = 1 / f = (n - 1) * (1 / R_1 - 1 / R_2)

Since our R_2 side is not supposed to be concave as shown in figure 1, but convex, I am assuming this is is done by making R_2 negative:

==> diopters = 1 / f = (n - 1) * (1 / R_1 - 1 / -R_2) = (n - 1) * (1 / R_1 + 1 / R_2)

I am assuming a lens thickness of 1.5mm ==> abs(R_2) = R_1 + 1.5mm

==> diopters = 1 / f = (n - 1) * (1 / R_1 + 1 / (R_1 + 1.5mm))

Plugging in our lens properties...
Refraction index of polycarbonate in the middle of the visible spectrum: n = 1.585
Diopters = 8.75/m
... and solving for R_1...

==> R_1 = 133mm

Our lens would be a piece of the surface of a sphere with an inner radius of 13.3cm. Doesn't seem implausible. Sound about right? (Hope I haven't violated the rule of never doing math in public :behindsofa:)
 
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As long as the les fits and doesn’t give any distortion - base curve is just a number.

Far more important for actual glasses than sunglasses.

C52F498E-A0FA-4D69-B473-B82D72E2B401.jpeg


This equation proves it - it’s Schroedinger’s cat equation that says - reality is in the eye of the beholder. So if a person is happy with their base curve and are honest to themselves that it works - then it works.

The moon only exists when you look at it.
It’s this fact that made Einstein ditch his theory of relativity for about 40 years. 😎
 
OK, but then the "industry standard" deviate from the optics definition used in other places where "plano" means that the lens has (one) flat surface. I'm not testing you, just curious why/if glasses use different nomenclature than photo optics, which wouldn't be too surprising.



No, not per my definition! 😂 I'd call it a meniscus when both surfaces are facing the same way and none of them are plane. ;)

Never heard of "plano power", but I'm sure you know that better than me. 😊

Ain’t the Meniscus the bit of water surface tension that curves up at the edge of a glass..? :)
 

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