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Base Curve Definition
- Thread starter andr3
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flyer
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C’mon guys!
Its SUNDAY for pete’s sake...
Last edited: WavecloudCustoms
Wavecloud Customs dot com
This even looks like me lol
I'm not sure I fully follow. The biggest issues for me is I don't see where lens thickness is part of that formula. But almost now importantly, you wouldn't plug in 8.75 diopters. Because it's a curve of 8.75 Diopters not 8.75D of power... You are wanting to find out the curve of a Plano "no power" lens. You aren't trying to find the radius of curve on a +8.75 or -8.75 diopter lens are you?@Chris A Hardaway. A little plausibility check for me to see if I am on the right track :
View attachment 741365
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
)
So the focal length will be infinite meters. This is showing a diverging lens formula best I can tell. You don't want a diverging lens or a converging lens. You wanted a non-RX Plano powered lens (0 diopters).
here (the thickness is a function of R_1 & R_2. If they are defined, the thickness is defined):
"
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))
"
Sure did...
"
Diopters = 8.75/m
"
so to write it out in full:
8.75/m = (1.585 - 1) * (1 / R_1 + 1 / (R_1 + 1.5mm))
I don't know about the terminology. I was trying to determine the radius of the imaginary surface of a sphere a lens is cut out of.
I don't think you are understanding that I'm saying you are trying to figure out the radius of curve on a zero (Plano) RX lens. So you can't use 8.75 as you're Diopters. The power is 0, so diopters is d= 0 not 8.75, focal length is infinity. Or am I missing something? Maybe this is beyond me sir.
Also thickness is not defined by the R1 or R2.... Only power of a lens is defined (d = diopters) by r1 and r2.
So you could have say two equal curves say 1 meter curve radius, on both front and back, thickness could be 1mm , 1 cm, or 1m for that matter. Thickness is certainly not determined by this equation. Diopters/power and radius of curve is. Right?
I actually took that from your initial post. Well, might be too complex to discuss w/o actually talking in person and making sketches for illustration. Either way, thanks for your input Chris. I believe you pointed me in the right direction. Much appreciated!
Just remember 8.75 diopters is a way to measure both curvature, or power, Not both. But it's ok. It would make more sense if I explain in person, or you review my first two posts again.I actually took that from your initial post. Well, might be too complex to discuss w/o actually talking in person and making sketches for illustration. Either way, thanks for your input Chris. I believe you pointed me in the right direction. Much appreciated!
Glad you are geeking out though!Similar threads
