can anybody tell me WHICH FACTORS affecting centringin cr39 flat top dbifocal
while surfacing:hammer:
can anybody tell me WHICH FACTORS affecting centringin cr39 flat top dbifocal
while surfacing:hammer:
Not sure what the question is but....Originally Posted by nixg
If you are laying off and blocking correctly and the centres arent OK then you may have unwanted prism being worked on the lens.
Rick
I am pretty sure I can.
please tell me what you know
Ask a question.
Surfacing a flat top?
The only thing I can tell you is that the distant OC is put in relationship to the center of the bifocal. No centration is really controlled in surfacing. Unless you have a prism problem. That usually comes from the blocker or the Generator.
JimMiller ABOC
I am sorry. "Surfacing a flat top?" is not really a question. In the old days we surfaced everything on optical center. As the lenses and frames got bigger, we had problems with prism due to the off center situations this created. That is the main reason why the blocks have extra hole in them for the surfacing machines. Now days most of the time we grind the lenses on geometic center and grind prism to place the optical center where we need it to be. This works in most cases except when the lens is a strong plus and you wing up cutting away the edge of the lens. Then you wind up off center again. The computer programs are pretty good most of the time. It does help to know how the computer are making these calulations though. I really don't know if I have answered you "question" or not. Please let me know.
Dear Jim,
Thank you for replying me,
We do have Gerber coburn blocker step one and gercber coburn sgx generator.
We are calculating tools with theire Innovation calculation program.
Now the problem is one of my customer always wanted optical centre [oc] 1.5 above segment and decentered 3mm from reading centre that is from segment. Above setup which i mentioned have facility to adjust centre directly from innovation program. But when i tried this one i a not getting oc perfectly on the spot which i want.
So i asked to the engineer of Gerber coburn so he told that for perfect oc your semifinished flat top should have perfect oc otherwise it will not work.
Is this true or any other problem is there.
Please guide me.
1. Tell me what you're doing in Innovations to specify the PRP location. ("PRP" stands for "Prism Reference Point", which is a more appropriate term than "OC".)
2. Tell me what result you are getting, and how you are measuring it. Include the Rx.
I have not used that program. I will say if it's worth anything, there should be an entry field for the BOC, or below optical center (how far the top of the seg is below the optical center). The oc placement from the seg PD should be controled be the near and distance PD. If you wish the distance PD to be 1 mm wider than the near, enter it one MM different on a monocular system two different for a binocular system. If you want to drive this customer crazy (and probably out of the optical bussiness) tell them to start spotting the near PD with the lensometer.
It's actually quite simple to enter the position of the PRP directly, in whatever terms are most convenient (e.g., inset or PD), but nixg may not be doing it correctly, which is why I asked.
Is this 3mm for both lenses.. with a decentration of 1.5 for each eye?
The reason why I ask, is it sounds to me that he is wanting a the difference between the far pd and the near pd to always be 3mm. So if the near pd is 57, he wants a 60mm distance pd.
When I used innovations, I normally used an interfacing program with it. The few times I got a chance to play with the system itself, I believe there was a spot to put near and far pds in manually, along with specifiying the oc placement.
Did you try it just the once, or has every time you tried this job, it has come up wrong? I guess what I am looking for is consistancy. It is possible for the calculations to be right, but something happened in the blocking, or other processes in the lab to cause an undesired result.
Cassandra
"Some believe in destiny, and some believe in fate. But I believe that happiness is something we create."-Something More by Sugarland
At his point, we know neither what was done (in terms of entering the order), nor what result was obtained.
If you are an optician... why are you letting your customers tell YOU what centration they want.
If you run a surfacing lab, supplying opticians, then you need to surface it right. normally the DOC will be 4 above and 2 in from the centre of the seg top, so why not try decentering the lens away from the normal position (set the lens up normally, then move the lens down 2.5 mm and in 1mm more)
The position of the NOC is a tricky one, and is often different from the position of the centre of the seg top. If you are surfacing for an optician you need to get them to clarify if they require DOC to be 3 mm out from Seg top centre, or NOC. If they say NOC, ask them to specify it in terms of from the seg top centre, and let them worry about the calculation for resultant NOC position.
Does the customer really want a difference of 6mm between NOC and DOC? never measured that once yet in 18 years!
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