Okay, I keep getting two different answers on this question:
When measuring a seg height do you measure to the bottom of the lens and add .5mm, or do you measure to the bottom of the frame?
Thanks in advance!
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Okay, I keep getting two different answers on this question:
When measuring a seg height do you measure to the bottom of the lens and add .5mm, or do you measure to the bottom of the frame?
Thanks in advance!
In the lab we measure to the bottom of the lens.
Do you add the .5 mm to make up for the groove or not?
Thanks!
I usually measured to the bottom of the lens and added half of the frame thickness. So, if you have a chunky zyl frame, you might end up adding 1mm. If you have a metal frame, it usually works out to 0.5mm.
In wholesale work I was always taught the bottom of the lens, period. My customers may be calculating this before I get the Rx.
Same here.Quote:
Originally Posted by Pete Hanlin
I don't think it matters which way you take the measurement as long as the person edging and fitting the lens knows how you measured it.
I find it better to measure the height above or below the datum line. Flat tops in general lie 2mm below the datum and PAL's tend to sit at about 4mm. See previous post in the Prog lens forum for technique.
Lewy
Thsi issue should not even be discussed. Any lab or lab personale you give an RX to make will work, surface, cut and mount the the lens by following the international rule...................bottom of lens to whatever you indicateQuote:
Originally Posted by Lewy
Yes, Chris, but do you think that the bevel is "the bottom" or is the most inferior portion of the lens front surface "the bottom"?
I was taught to do what Pete described...is that not standard?
In over 20 years in the field, I have never worried about the 1/2 mm hidden by the frame. I measure to the lowest part of the lens, and never have a problem.
Bottom of the lens. If the edge is beveled then to the bevel apex. A "Box-O-Graph" can be used to confirm the accuracy of your measurement method. Bevel depths are about .3mm for metal frames and about .5mm for zyl. Rolled eyewires may make accurate measurements difficult unless the lens is removed.
It should be to the lowest point on the lens, including bevel.
DRK, Actually the bevel is the bottom. In the old days some lens manufacturer supply some transparent thin rulers, you would place into the frame groove and take you reading where needed...........and that would give you the right measurement. The labs will then use top to bottom meausure,Quote:
Originally Posted by drk
Bottom of the lens, which on a v-bevel is the bottom of the bevel. Like Pete, I estimate. That's how I was taught, some 45 years ago.
Has anyone here actually had a case where half-a-mm actually made a difference in a patient's adaptability?
I usually measure to the bottom of the visible portion of the lens and have had VERY few problems in my 8 years of experience.
Finklstiltskin, it works fine the way you just mentioned. we have been doing it that way for over 45 years with no problems.Though we are very meticulous with the seg or pupil height measurement(within .5mm) we don't worry about the .3, .4,or.5mm bevel depth.Not much of an optician if you can't adjust the glasses for minimal errors. Obviuosly on rimless frames it is measured to the very bottom.