Hey - John here. Just to be clear: These 9 examples came from a question sheet that was sent to me by a member. She asked me to work them out for her so I did. Someday I'll do another one and use examples that are a little more realistic. Some of the numbers on the sheet were a little, well, odd. Thanks for understanding.
The prescription +2.00 DS/+2.00 DC x 135 is made as a lens with a -4.00 D toric base curve.Disregarding lens thickness, what is the power of the front surface
Hi John. Can you explain why transposition doesn't change the optical power of the final product? I'm trying to understand how that's possible, given that a spherical power is the same on all meridians. For example, if a prescription is written as +1.50 / -2.00 x 90 and you transcribe it to -0.50 / +2.00 x 180, then the power on all meridians becomes -.50 which is an entirely different type of lens (concave with negative power) instead of convex.
Dave, Weird - It's 1/2/2018 and my day will begin by starting to review this video to reshoot it with better examples! It has been on my mind for a few months now. John
The aspheric design is pre-molded at the factory on the front base curve of the lens in both stock and surfaced lenses. Think of the old flying saucer profile: a center "bubble" which is spherical and then it tapers off to a flatter smoother, less steep profile. The language sort of changes when you get to the backside depending on the surfacing technique. A true free form backside although technically aspheric isn't called that.
Thank you for the videos. Just wondering when transposing into toric form and we are given the SPH Curve, how do we know when to do simple transposition first. I am unsure when should the given cyl be positive and when should it be negative.
I'm not 100% sure what you are asking but --- lenses are physically constructed in minus cylinder so ALL optical formulas, math, explanations begin with the powers written in minus cylinder. So if you ever have + cylinder form do your flat transposition first. Front base curve + back curves minus so cylinder must be minus right? If I'm missing something drop me an email. John
Hi thank you for your explaning very well though I have aqu! Last step in putting the cyl outcome we put it the sign - bacause it's cyl or according to substrate the more num and less numm? Thank you
Hey - John here. Just to be clear: These 9 examples came from a question sheet that was sent to me by a member. She asked me to work them out for her so I did. Someday I'll do another one and use examples that are a little more realistic. Some of the numbers on the sheet were a little, well, odd. Thanks for understanding.
Hi, may I ask why the axis after transposition is taken from the axis of base curve instead of cross curve ?
The prescription +2.00 DS/+2.00 DC x 135 is made as a lens with a -4.00 D toric base curve.Disregarding lens thickness, what is the power of the front surface
Hi John. Can you explain why transposition doesn't change the optical power of the final product? I'm trying to understand how that's possible, given that a spherical power is the same on all meridians. For example, if a prescription is written as +1.50 / -2.00 x 90 and you transcribe it to -0.50 / +2.00 x 180, then the power on all meridians becomes -.50 which is an entirely different type of lens (concave with negative power) instead of convex.
You want this video: th-cam.com/video/rVMW5a6qJ6I/w-d-xo.htmlsi=siAoBKwHQuJ-HCf1
Toric transposition and flat transposition are two different things.
@@LaramyKOptical Thank you. I will watch the video.
Awesome! Nice and clear explanation, thank you!
Dave, Weird - It's 1/2/2018 and my day will begin by starting to review this video to reshoot it with better examples! It has been on my mind for a few months now. John
Laramy-K Optical Oh really? Well, I look forward to that video too!
thanks for all the videos, I am interested in how to produce aspheric lens, their materials if any and process
The aspheric design is pre-molded at the factory on the front base curve of the lens in both stock and surfaced lenses. Think of the old flying saucer profile: a center "bubble" which is spherical and then it tapers off to a flatter smoother, less steep profile. The language sort of changes when you get to the backside depending on the surfacing technique. A true free form backside although technically aspheric isn't called that.
thanks for such good explanation.
Thank you for the videos. Just wondering when transposing into toric form and we are given the SPH Curve, how do we know when to do simple transposition first. I am unsure when should the given cyl be positive and when should it be negative.
I'm not 100% sure what you are asking but --- lenses are physically constructed in minus cylinder so ALL optical formulas, math, explanations begin with the powers written in minus cylinder. So if you ever have + cylinder form do your flat transposition first. Front base curve + back curves minus so cylinder must be minus right? If I'm missing something drop me an email. John
Sir after changing additional number prescription to near vision prescription can we transpose that prescription if transposition should apply??
th-cam.com/video/rVMW5a6qJ6I/w-d-xo.htmlsi=z60FPMs1IBKvZbz2
Hi thank you for your explaning very well though I have aqu!
Last step in putting the cyl outcome we put it the sign - bacause it's cyl or according to substrate the more num and less numm?
Thank you
I think it’s easier if you go by the formula , recognise first which one is DL , D1 or D2 then you work the formula ... ✌️
There is some video on TH-cam. They change the BC axis 90 degree apposite, why?
Really can't say why.
Thank you so much for this.
You are welcome. Track down the follow up versions - they use more realistic numbers.
I think the one at the right is the back curve, while the left is the cross curve.
What does DL, D1 D2 mean ??
Nice
Good
👏👏👏
I am confused 😢
If you generate power in this way 🙄 i think u will lose your lens in case of bifocals and progressive lenses as those transpositions wrong 😢
I use the word "conceptual" about twenty times in that video! I say, "With the introduction of free form this all became just a concept or theory."
Please
Nice