Hi my name is Rafael i`m 28 and i am from germany. I have found this awesome bord surfing the web.
Here in germany we donīt have such a website, forgive me if but my english is not the best.
I have a problem with progressive lenses and prism thinning
For examle i have this RX:
R: sph -2,75 cyl +0,5 A: 0 Add 2,25 Prism 0,71cm/m Bas:315
L: sph -2,25 cyl +0,25 A:175 Add 2,25 Prism 0,71 Bas:135
Equipmend:
LOH R-Xpert calculating software
LOH PRA Blocker (Axis calibration is done)
LOH V-Pro Generator (Rms Prozess)
LoH Toro X for polishing
The problem is the result prism, calculated from the software is not matching with the job card.
Itīs a problem to verify this.
So i make a few test.
1 Test: I deactivate the prism thinning from the calculating software.
I have finishe then the lens with the new calculation without prism thinning.
I should verify this results:
(Blocking was done at PRP Point, fitting high to Cross was 4mm)
For the Right Lens I must habe 0,71 cm/m Bas:315 or 0,5 cm/m Base 0
0,5 cm/m Base 270
For the Left Lens I must habe 0,71 cm/m Bas:135 or 0,5 cm/m Base 180
0,5 cm/m Base 90
But after the Lenses Was finished i get this:
For the Right Lens I get:0,5 cm/m Base 0
1,5 cm/m Base 270 so resulting prism is 1,58 cm/m Base 288
For the Left Lens I get: 0,5 cm/m Base 180
0,5 cm/m Base 270 so resulting prism is 0,7 cm/m Base 225
I was going crazy, so i have take the same half-finished Blancs an take look what they measured
at the PRP befor i will surfacing them. I was suprized because i have measured a vertical prism
for about 1,0 cm/m base down. Both lenses right and left have for the Add of 2.25 a base down prism
of 1,0 cm/m. So i took a look for more lenses of this Add and figured out there was about 1,0 - 1,2 prism
Base down on them.
So i make an next test:
Test 2: I have calculatet the same RX with the RX Calculating software and put in the field Thinprism,
the 1,0 cm/m Base down, that I have measured in the PRP point on the half finished blancs.
I must put this with -1,00 in the software.
My Idea was do get a prism at the PRP point to 0, so i have only the Prism that the client would have.
SO i have finished them get this:
For the Right Lens I get:0,52 cm/m Base 0
0,50 cm/m Base 270 so resulting prism is 0,72 cm/m Base 316
For the Left Lens I get: 0,50 cm/m Base 180
0,49 cm/m Base 270 so resulting prism is 0,70 cm/m Base 136
The Results was very fine for me so, but what do you think about. Is this the right way.
Ok the lens thickness is not looking good, the lenses are thicker, but I have in the
lenses the results that the client will have. And the co-worker have no problems with controlling.
But is this Base down prism on the PRP normal in the half-finished Lens?
If it should be normal, any ideas i can modify the calculation to get this compensated?
I hope you can help me
Rafael
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