Tolerance on Polarization Axis

[edKENdance]

Obviously dead on 180 is what you want to have but what sort of tolerance do you allow on passing a polarized lens? We cut off at about 5 degrees off. Is that too much?

[Chris Ryser]

Obviously dead on 180 is what you want to have but what sort of tolerance do you allow on passing a polarized lens? We cut off at about 5 degrees off. Is that too much?

Dead on 180.............no tolerance if you dont want the customer come back or go somehwere else next time, if he had used this type of lens before.

[rsandr]

Dead on 180.............no tolerance if you dont want the customer come back or go somehwere else next time, if he had used this type of lens before.

Im not arguing, its just one of those things that has me baffled.

We always head for dead on 180 but I wondered that if the lens is designed to block out reflection from a horizontal plane surface then it would only matter if they were 90 off.

Maybe you can help me understand this better.

Regards,
Rick

[Chris Ryser]

We always head for dead on 180 but I wondered that if the lens is designed to block out reflection from a horizontal plane surface then it would only matter if they were 90 off.
Rick

If I remeber right (without checking back), the lens will cut off reflection at 41 degrees from a horizontal plane. As the person looks straight it will cut off reflection at the angle of 41 degress at the axis it is mounted. Therfore you would see all reflection coming form a 180 plane.

[Darryl Meister]

I think 2 degrees would be a reasonable tolerance.

[Darryl Meister]

If I remeber right (without checking back), the lens will cut off reflection at 41 degrees from a horizontal plane.

I think you might be thinking of Brewster's angle (the angle of reflection at which light becomes completely plane-polarized off a dielectric surface), which is independent of the axis of the Polaroid film. For a given surface, Brewster's angle is constant, though the optimum axis of the Polaroid film will depend upon the orientation of the surface; generally we are worried about horizontal surfaces, like water, so we use axis 180.

[jherman]

Am I missing something, if a lens is edged are you guessing when checking the axis of the PVA?
Is there a more appropriate way to check PVA axis on an edged lens?

[shanbaum]

Am I missing something, if a lens is edged are you guessing when checking the axis of the PVA?
Is there a more appropriate way to check PVA axis on an edged lens?

How about taking an uncut polarized plano, and rotating it in front of the mounted lens? At a particular orientation of the uncut, the system will become almost opaque; the axis of the mounted lens will be 90 degrees away from the orientation of the uncut at which that near-opacity occurs.

[jherman]

That is the only way I know also, I wasn't sure if there was a more exact way to determine the axis of PVA.

How about taking an uncut polarized plano, and rotating it in front of the mounted lens? At a particular orientation of the uncut, the system will become almost opaque; the axis of the mounted lens will be 90 degrees away from the orientation of the uncut at which that near-opacity occurs.

[Darryl Meister]

Am I missing something, if a lens is edged are you guessing when checking the axis of the PVA?

This would primarily apply to surfaced, uncut lenses that still have their film reference / axis markings.

[RGC_man]

After a long delay from the supplier I have been known to glaze lens off axis (but within European tolerances) to keep them polarized. The same works for round segs to get a little extra decentration.