Dear essegn, wich lab software are you using?
-------Bifocal lenses are being produced on Satisloh line and progressives on Optotech Freeform machine, so we are using the RX program from mentioned companies.
PM i can give you a excel sheet for this. You can use then the amout of needed prism the excel sheet give you in every RX Calculation software, to calculate the proper additional thickness you will need for process the slab off (especially on minus lenses).
------I'm not sure if you think the xls that you sent me before >
http://www.optiboard.com/forums/show...ting-Cross-NRP
------As you wrote to calculate additional thickness.. Doesn't the vertical imbalance mean that we should decrease the thickness - and that means slab-off ?
---- Is the slab off the same for bifocal and progressive lenses ?
Backside Slab Off on Hard Lap Tools Howto:
1) use the excel sheet to determine the amout of Slab Prism
2) Calculate the RX with the additional needed prism from excel sheet (Base 90)
---- if you think the mentioned xls file, i don't know which parameter do you mean..
---- i can see there> Prism fitting cross,Prism imbalance Fitting cross, Prism imbalance NRP
---- do you mean to set the additional needed prism to our RX program? If so, we have the only possibility to set it to the collum: Prism or Prism base
3) Determine additional thickess on minus lenses donīt go under 1.8mm @ B270
---- how can I determine additional thickness? We have set in our database the center thickness of minus lense to 1.7
4) Note the Center thickness
5) Take away the additional slab prism out and calculate the normal RX with the noted center thickness
------ point 2 above..
6) Block the lenses how you will do it normally
7) Generate the Lens with the additional Prism from the Excel sheet Base 90, take care you put the lens in the correct direction!!! (Tell me wich generator you use)
----- we have two generators - Satisloh (convetional line) and Optotech (Freeform)
8) Surface the normal way, but donīt deblock the lens
9) Fill up the Lens with resin, wait the time you need for surfacing
------ what does it mean full up the lens with resin ?
10) Generate the lens again (take care correct direction), but donīt generate to the end E Value, let it thicker. As far the Slab Line apears, reduce the material removal (0,5 mm is ok).
----- i can't imagine how the slab line look like
----- could we get the slab line on bifocal and mulifocal as well?
11) Control the Slab Line, if not straigt you can correct it with the generator. With little prism in Base 0 or 180. Or you correct it till smoothing, with pressure on the lens Base 0 or 180.
----- what kind of correction do you mean ?
12) Smooth the Line down as you will design you slab.
I make Bifocal on the segment line
Progressives 3 to 4 mm under prism reference point.
But take into account the stock remove on you polishers, depends on you polish
---- what does it mean to do bifocal on the segment line? moving of optical centre to the top of segment ?
---- progresice 3 to 4 mm under prism reference point? Do you mean two lenses with different dpt power have the same prism under 3-4mm under PRP ?
13) Polish the Lens and control it
14) deblock, remove epoxy.....
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