Polarised Sunglasses.
Discussion
Not sure where to put this, 0please move if needed.
Polarised Sunglasses.
How can you tell if they are polarised the wrong way?
Wife has had a pair supplied by the 'should have gone to' shop and maybe we shouldn't have. She picked up her polarised sunnies this week and she complained that they made her 'feel funny'.
I know a bit about polarisation from my camera days, so tested by looking at a reflection and then rotating through 90 degrees. Madly one lens worked one way and the other worked the opposite way! No wonder they made her feel a 'bit funny' obviously wrong and as this was the third attempt at getting her glasses right they have been returned and credited.
But this got me to test mine. Both lenses are polarised in the same direction, but in my mind the are both wrong. If I look at a reflection in a window with them on my nose I see the reflections, if I turn them through 90degress again and look through one of the lenses the reflections disappear and I can see through the window.
Is this right?
V
Polarised Sunglasses.
How can you tell if they are polarised the wrong way?
Wife has had a pair supplied by the 'should have gone to' shop and maybe we shouldn't have. She picked up her polarised sunnies this week and she complained that they made her 'feel funny'.
I know a bit about polarisation from my camera days, so tested by looking at a reflection and then rotating through 90 degrees. Madly one lens worked one way and the other worked the opposite way! No wonder they made her feel a 'bit funny' obviously wrong and as this was the third attempt at getting her glasses right they have been returned and credited.
But this got me to test mine. Both lenses are polarised in the same direction, but in my mind the are both wrong. If I look at a reflection in a window with them on my nose I see the reflections, if I turn them through 90degress again and look through one of the lenses the reflections disappear and I can see through the window.
Is this right?
V
The OP isn't as stupid as it sounds. I had a pair of prescription lenses that were polorised at 90 degrees to the "correct" way.
Proof was, looking out across a lake, you should get less glare and be able to see into the water better. But these glasses made the reflection from the water even worse. I eventually got them to admit the mistake and re-make the lenses.
I have had many pairs of polorised lenses, and these were the only ones that ever had this problem.
Proof was, looking out across a lake, you should get less glare and be able to see into the water better. But these glasses made the reflection from the water even worse. I eventually got them to admit the mistake and re-make the lenses.
I have had many pairs of polorised lenses, and these were the only ones that ever had this problem.
kambites said:
I have no idea which way mine are polarised buy they certainly don't stop reflections in any window I've ever seen. They are polarised the opposite way to my car stereo screen, which is mildly annoying. 
Yeah, not much good in a glass cockpit either as the ND & PFD disappear if you look at them from a certain angle!!! FurtiveFreddy said:
I understand all of that, but it doesn't answer the question of which way they should be polarised, who chooses and why?Surely I should be somewhere between glass and liquid/water.
V.
VEX said:
Surely I should be somewhere between glass and liquid/water.
The answer, I suppose, is that they should be polarised to filter out reflections from horizontal surfaces since they are what tend to cause practical issues (roads, water, etc.); which means the polarisation of the glasses should be vertical?VEX said:
kambites said:
Yeah, I thought the OP meant a reflection of himself in the window which would obviously be at 90 degrees.
Surely I get reflected at 180 degrees, 90 isn't possible. I can't even work out what you would see if I was reflected at 90! 
Although thinking about it, maybe that's considered a "zero degree" reflection, I can't remember which angle you traditionally measure now. It probably varies.
Edited by kambites on Saturday 14th March 17:39
But the polarisation of the glasses did cancel out the reflections. It was just that the cancelation effect only happens when the glasses and lens were rotated by 90degrees and obviously I can't wear them like that!
What I am trying to find out is what the correct orientation of the filters (polarised lenses) should be.
V.
What I am trying to find out is what the correct orientation of the filters (polarised lenses) should be.
V.
VEX said:
But the polarisation of the glasses did cancel out the reflections. It was just that the cancelation effect only happens when the glasses and lens were rotated by 90degrees and obviously I can't wear them like that!
What I am trying to find out is what the correct orientation of the filters (polarised lenses) should be.
V.
I think from the page linked above that the correct orientation is vertical, so they cancel out the reflection from horizontal surfaces. This will mean that they don't cancel glare from vertical surfaces (such as windows) though. What I am trying to find out is what the correct orientation of the filters (polarised lenses) should be.
V.
VEX said:
But the polarisation of the glasses did cancel out the reflections. It was just that the cancelation effect only happens when the glasses and lens were rotated by 90degrees and obviously I can't wear them like that!
What I am trying to find out is what the correct orientation of the filters (polarised lenses) should be.
V.
They should IMHO cancel out the reflections from the horizontal plane (sunlight across water/road/etc.) rather than the vertical plane. The latter is great for seeing through shop windows at more than the Brewster angle, but is that really a problem you need to solve?What I am trying to find out is what the correct orientation of the filters (polarised lenses) should be.
V.
Qualified optician here.
Look through both the lenses simultaneously at a TV/ computer screen. Rotate the glasses (hold them out infront of your face- you'll struggle if you try this whilst actually wearing them!) until the display appears completely black/ blank. This should happen at the same time through both lenses- if they blank the display at different points/ axes then they haven't been glazed correctly.
Polarised lenses arrive from the manufacturer with markings which allow the technician to glaze them on the correct axis. These markings are normally left on the lenses after glazing is complete so that the practice can check they have been correctly glazed before notifying the patient their glasses are ready for collection.
There are therefore multiple opportunities (manufacturer > glazing lab > practice) for any decent optical business to spot incorrectly glazed polarised glasses before they reach the patients' face and cause problems. Take them back if in any doubt.
Look through both the lenses simultaneously at a TV/ computer screen. Rotate the glasses (hold them out infront of your face- you'll struggle if you try this whilst actually wearing them!) until the display appears completely black/ blank. This should happen at the same time through both lenses- if they blank the display at different points/ axes then they haven't been glazed correctly.
Polarised lenses arrive from the manufacturer with markings which allow the technician to glaze them on the correct axis. These markings are normally left on the lenses after glazing is complete so that the practice can check they have been correctly glazed before notifying the patient their glasses are ready for collection.
There are therefore multiple opportunities (manufacturer > glazing lab > practice) for any decent optical business to spot incorrectly glazed polarised glasses before they reach the patients' face and cause problems. Take them back if in any doubt.
Thanks DoE.
They are back with the optician now. My (basic) understanding of polarisation is that I shouldn't be able to see reflections in one plan and see them a 90degree change. So if I can see reflections in a window when on my nose but not when rotated through the 90 as you describe, is this right or wrong?
Don't mind which, just doesn't make sense to me.
They are back with the optician now. My (basic) understanding of polarisation is that I shouldn't be able to see reflections in one plan and see them a 90degree change. So if I can see reflections in a window when on my nose but not when rotated through the 90 as you describe, is this right or wrong?
Don't mind which, just doesn't make sense to me.
Reflections like that are very hard to pin down - it's heavily dependent on the surface of the item you're reflecting from.
Another easy way to tell is take the lenses out, hold one in front of the other and rotate one. If there isn't a 90' difference when they darken each other then they're not right.
Another easy way to tell is take the lenses out, hold one in front of the other and rotate one. If there isn't a 90' difference when they darken each other then they're not right.
Thanks DoE.
They are back with the optician now. My (basic) understanding of polarisation is that I shouldn't be able to see reflections in one plan and see them a 90degree change. So if I can see reflections in a window when on my nose but not when rotated through the 90 as you describe, is this right or wrong?
Don't mind which, just doesn't make sense to me.
They are back with the optician now. My (basic) understanding of polarisation is that I shouldn't be able to see reflections in one plan and see them a 90degree change. So if I can see reflections in a window when on my nose but not when rotated through the 90 as you describe, is this right or wrong?
Don't mind which, just doesn't make sense to me.
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