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Thread: Why is it so?

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    Member formerly known as : Lplates Glenda's Avatar
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    Why is it so?

    Just bought a new phone, primarily because of its camera and have been experimenting with it. Works fine in each orientation at home but as soon as I took it to the local marina, I could see the screen clearly in portrait orientation but as soon as I swapped to landscape, all I saw was my reflection. Thought I had accidentally pressed something but couldn't work out what. My husband said he could see the screen clearly both ways. This morning I took off my polarised sunglasses and hey presto I too could see the screen clearly in landscape mode too. No idea why a pair of sunnies would make a difference due to the phone's orientation
    Glenda



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    Polarizing works by letting light in from only one layer. If you put two polarized sunglasses together then turn one at 90 degrees you can not see through the glasses. So I guess the camera screen is polarized

    J S Millar
    Last edited by thegrump; 21-05-2017 at 1:17pm. Reason: adition
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    Administrator ricktas's Avatar
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    As TG says, It is exactly how polarisation works. Even the word polarisation.. relates to the angles to the Poles (North South).

    Funnily, when I got my new car about 2 years ago, I was weirded out. The window tint is polarised, and when I wear my polarised sunnies while driving, it was creating cross polarisation and I was seeing rainbow effects on all sorts of every day objects.

    I also have a 3D tv, and if I have the 3D glasses on, I cannot read my phone at all.

    Isn't polarisation amazing?
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    can't remember Tannin's Avatar
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    Thegrump is on the right track. Your glasses are polarised, of course. And all LCD screens are polarised. That's how they work. There are several variations in detail, but the basic idea is that you have a bright light in the back and two polarised screens in front of it, sandwiched together and set at 90 degrees to one another. One of them is permanent, the other one (let's say it's the front one) is under electronic control.

    Normal iight (such as the light from the LED or fluro behind your phone or computer screen) is randomly polarised. Some of the light waves go up and down, some from side to side, some at in-betwen angles. So a horizontal polarised screen (such as your sunglasses) cuts out half of them - the ones that "can't fit" between the "slats" of the polarisation because they are going up and down. The sideways-oriented light beams pass straight through the slots. This is how a polarising sunlght filter on your lens works: it cuts out half of the randomly-polarised light bouncing off the scenery, but more than half of the light coming from the sky, because it hasn't been mixed up by bouncing off random objects yet and is still mostly polarised in the same direction. You twist the circular polarising filter to cut more or less of that sky brightness out until you are happy with the result.

    So the fixed back polarising screen of our imaginary phone or computer cuts out half the backlight and lets the other half pass through. With no power applied, the rows and rows of tiny polarising filters in the front part of the screen are vertical, so they block the other half of the light. Apply power to the little filters and they rotate. If they rotate 45 degrees, they let through half of the light striking them (or one quarter of the total original light - the back filter has already blocked half of it, remember) and you see a mid grey. If they twist the full 90 degrees, they let all of the light striking them pass through and you see a white dot.

    (In practice, you also have a layer of coloured filters, so the front screen is actually blocking little patterns of coloured light, but we can ignore that for current purposes.)

    Notice that all of the light given off by the screen is horizontally polarised (because of that fixed-in-place back filter). When you look at the screen through sunglasses, what happens? Nothing! Your glasses are horizontally polarised, and the light striking them from the screen is all polarised in the horizontal plane, so it passes through the glasses as if they were not there.

    Now turn the screen sideways. The light it gives off is now vertically polarised, and your horizontally polarised glasses block 100% of it. Or you can turn the glases sideways instead and get the same result. Notice that if you turn them both sideways, the light is vertical, your glasses are vertical too, and you can see the screen normally.
    Tony

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    Member formerly known as : Lplates
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    Thanks TG and Rick - that explains it. I too have tinted windows in the car and often experience the rainbow effect. I also remember the first time I looked through the viewfinder with a CPL attached and my polarised sunnies on - very trippy effect. I knew both that was caused by the double polarisation but couldn't work out why it was only affecting my ability to see the screen in landscape but no effect in portrait. Obviously the 90 degree angle you mention TG was the cause.

    Thanks Tony for your detailed explanation.
    Last edited by Glenda; 21-05-2017 at 2:18pm.

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    can't remember Tannin's Avatar
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    Bit off-topic here, but that's one thing I dislike about my new car: it has tinted side windows. On a nice warm day, you can look out and think "that's lovely light, I think I'll stop and take a picture". Then you stop and get out and it's harsh and flat and ugly. You have to keep winding the windows down to see outside properly and judge the light. I daresay I'll get used to it eventually. I have thought about getting the glass replaced, at least for the front windows, and stasndard clear glass windows are readily available from any windscreen place, but it would cost maybe $500 and that seems a lot to spend when I can probably just learn to make allowances.

    This is why I practically never wear sunglasses: I like to see the quality of the light. Less of an issue down your way, I reckon. Being so much further south, the light tends to be pretty nice all day long. Out in the dry inland, you have to pick your moment better.


    (PS: I haven't tried turning the car 90 degrees to see if the view is better that way.)
    Last edited by Tannin; 21-05-2017 at 2:24pm.

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Reminds of the time I had bought a new PINT-AND-SHT. I saw an emu in a paddock, so I (pulled over and) stopped and took out the
    camera. I was always (in those days) in "live view" Imagine my consternation when I COULD NOT see an image in the screen!!!
    It was dark!! I raised my polaroid sunglasses to peer into the optical viewfinder and noticed in the peripheral vision that the view
    screen was ON and showing an image.

    I "got a shot" then looked back at the view finder. It was BLACK again. I uttered a few words like "Whot the hock...!", then stupidly
    realised what was happening. -- After that I got into the habit of removing the sun glasses to look at the view screen
    Last edited by ameerat42; 21-05-2017 at 6:06pm.
    CC, Image editing OK.

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    A royal pain in the bum! arthurking83's Avatar
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    Quote Originally Posted by Tannin View Post
    .....

    This is why I practically never wear sunglasses: I like to see the quality of the light. Less of an issue down your way, I reckon. Being so much further south, the light tends to be pretty nice all day long. Out in the dry inland, you have to pick your moment better.


    ....
    This is exactly why I do!
    When I'm out driving and scouting for a location to shoot a landscape, I'm almost always using a CPL filter on the lens .. so to see the landscape(in that particular orientation relative to the sun) is important to me.

    Plus: glare absolutely kills my vision(or I squint a lot), so if it's raining, or had been and road is wet, the polarising filter removes almost every trace of glare, and you can see the road!(ie. not the reflected silvery surface of the water!)

    I hate the darkening effect of sunglasses tho, so I'm hoping that one day some genius will invent polarising filters that don't darken!
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    Member formerly known as : Lplates
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    I couldn't be without my sunglasses and do prefer polarised ones. They are prescription ones for distance so I need them to drive and see birds if they are my prey, and like Arthur have always squinted without sunnies. The sun here is harsh and bright far more hours than it is mellow. Will just have to remember to take them off to see the phone screen.

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