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Thread: Up to 2 degrees

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    Up to 2 degrees

    ANSI standards say i can have up to 2 degrees of tilt in my multifocal lenses. how do i go about measuring those 2 degrees? ive looked all over for a layout chart and can find nothing on the web.

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    Quote Originally Posted by Dooky Shoes View Post
    ANSI standards say i can have up to 2 degrees of tilt in my multifocal lenses. how do i go about measuring those 2 degrees? ive looked all over for a layout chart and can find nothing on the web.
    Just search for pantoscopic tilt instead.

    Here's some info: https://www.odob.health.nz/wp-conten...f-D-Wilson.pdf
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    Quote Originally Posted by vfpamp View Post
    Just search for pantoscopic tilt instead.

    Here's some info: https://www.odob.health.nz/wp-conten...f-D-Wilson.pdf
    that has nothing to do with what i was asking. i'll give you an example.

    Lets say i have a freshly edged and mounted pair of bifocals. everything checks out on the lensometer. all my axis's and powers are spot on. BUT! the bi-focal segment is crooked by an undetermined amount. how would i go about measuring how far off of the 180 that segment is? or am i just coming at this all wrong?

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    Quote Originally Posted by Dooky Shoes View Post
    that has nothing to do with what i was asking. i'll give you an example.

    Lets say i have a freshly edged and mounted pair of bifocals. everything checks out on the lensometer. all my axis's and powers are spot on. BUT! the bi-focal segment is crooked by an undetermined amount. how would i go about measuring how far off of the 180 that segment is? or am i just coming at this all wrong?
    Ohh... But if the axis checks out for the distance part, doesn't that say that you mounted the bifocal segment of the lens correctly? If you rotate one, you have to rotate the other. The only option is a manufacturing defect on the bifocal blank (either on the axis of astigmatism or on the bifocal segment).
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    Can you turn the lens in the frame at all? In this scenario I would try getting the bifocal seg straight and then see if the cyl is within tolerance. If you can't simultaneously get the bifocal and cyl to be correct, that sounds like a manufacturing/surfacing error, as vfpamp said.

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    If you needed a precise measurement for determining how crooked a seg is, I'd just take it over to the lensometer and mark the 180 line on the mounted lenses and use a protractor to find the angle of the seg.

    I usually just hold a PD ruler across the top of both segs and make sure they are parallel to eachother. If they are way off to the point of needing a remake, it's usually plainly obvious without needing to use a tool or measure it.

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    Quote Originally Posted by vfpamp View Post
    Ohh... But if the axis checks out for the distance part, doesn't that say that you mounted the bifocal segment of the lens correctly? If you rotate one, you have to rotate the other. The only option is a manufacturing defect on the bifocal blank (either on the axis of astigmatism or on the bifocal segment).
    No. ANSI Z80.1-2015 has a tolerance of 14° for up to a .25 cylinder, 7° for .25-.50 cyl etc. So obviously the axis of the lens doesn't need to match the axis of the seg line to be withing ANSI suggested tolerance.

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    Quote Originally Posted by Kwill212 View Post
    No. ANSI Z80.1-2015 has a tolerance of 14° for up to a .25 cylinder, 7° for .25-.50 cyl etc. So obviously the axis of the lens doesn't need to match the axis of the seg line to be withing ANSI suggested tolerance.
    exactly! the place where this comes into play the most is with larger cyls. but i think that its more of a non issue than i was thinking at first.

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    Quote Originally Posted by Kwill212 View Post
    No. ANSI Z80.1-2015 has a tolerance of 14° for up to a .25 cylinder, 7° for .25-.50 cyl etc. So obviously the axis of the lens doesn't need to match the axis of the seg line to be withing ANSI suggested tolerance.
    oh I see. When you said "my axis's and powers are spot on" I assumed dead on, not only within the ANSI Limits.


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    Master OptiBoarder OptiBoard Silver Supporter Barry Santini's Avatar
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    All these are manufacturing/lab standards, not dispensing standards.

    B

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    OptiBoard Professional Mauro.Airoldi's Avatar
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    The reference in Europe is EN ISO 2187 and give you all the information

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    Quote Originally Posted by Barry Santini View Post
    All these are manufacturing/lab standards, not dispensing standards.

    B
    i work in a lab

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    Master OptiBoarder OptiBoard Silver Supporter ak47's Avatar
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    I don't think anyone has answered the OP's question, so I'll take a stab. ANSI HORIZONTAL SEGMENT TILT < 2 DEGREES CROOKED......I asked and answered this question of myself a while back with trigonometry knowing that the dots are 34 mm apart.....and the answer is slightly over a 1 mm vertical height difference between the nasal dot and the temporal dot. I used tangent (2 degrees = 0.0349066 radians) = x / 34...therefore x = 1.2 mm

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    Quote Originally Posted by ak47 View Post
    I don't think anyone has answered the OP's question, so I'll take a stab. ANSI HORIZONTAL SEGMENT TILT < 2 DEGREES CROOKED......I asked and answered this question of myself a while back with trigonometry knowing that the dots are 34 mm apart.....and the answer is slightly over a 1 mm vertical height difference between the nasal dot and the temporal dot. I used tangent (2 degrees = 0.0349066 radians) = x / 34...therefore x = 1.2 mm
    that would work for a progressive, but how would you do a bifocal?

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    Master OptiBoarder OptiBoard Silver Supporter ak47's Avatar
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    The line at the top of a FT28 is 26 mm long....so the difference in vertical height to be within 2 degrees tolerance from nasal side of seg line to temporal side would be (26/34) x 1.2 mm = 0.9 mm

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    A protractor is your easiest bet.
    I'm Andrew Hamm and I approve this message.

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