Something you didn't know about polarisers*

[Tannin]

Something really weird you didn't know about polarisers*

https://www.youtube.com/watch?v=zcqZHYo7ONs

* unless you are a physics geek, and possibly not even then.

[jim]

Quantum is thrillingly weird.

[ameerat42]

Quantum is thrillingly weird.

It is!/It isn't?/Is it?

[Tannin]

^ Ask the cat.

[arthurking83]

Definitely something I didn't know .. and yes I'm a geek!
(I have proof, which I'll tempt many of you to try for yourselves which will prove that you're geeks too!)

Firstly I think they've used the old (photographically speaking) linear polarising filter types.
These linear Pols are harder to find, but we all now buy the ubiquitous CPL(circular) .. coz apparently they work better for AF or metering systems or whatever.

So take your CPL go to a mirror, with good lighting in that room, and place it on the mirror with the MALE threads against the mirror. Important to have male threads(MT) for this to work. It could be a very very dark blue tint to it too. All my CPLs have this blue tint under fluoro and LED light. No incandecents here to observe any different colours.

Second test is to then flip the CPL on the mirror so that the female threads(FT) or of a slum no front threaded type, then the front of the filter is now against the mirror. It barely darkens at all now.

No amount of rotation will change these results. It'll be the same light transmission no matter how you rotate the filter against the mirror.

Then(if you have any) try the same with a linear polariser(LinPol) too. No matter which way you position or rotate the LinPol it doesn't darken against the mirror like the CPL did.

#3. if you have more than one polariser, LinPol or CPL, you can make it darken or not according to how you've positioned them relative to each other to varying degrees of rotation(to each other).

3a. if you have two CPLs positoned as tho they were stacked, ie,. MT to FT threaded, they only darken a very slight amount(not ultra dark). This method really changes colour more than anything else. In Sunlight, under the right conditions you see a strange propeller effect, two dark quadrants and two brighter quadrants .. like the BMW logo but blue and brown(that I've seen). Under room lights I've only ever seen a browning or blueing when each is rotated against the other.
3b. flip one around so that they're facing each other(ie. MT to MT or FT to FT). This is where they 'block' light, or more accurately reduce light dramatically. This, I think, is the premise of the expensive variable neutral density filter, but that this method gives a very strong colour cast!
3c if you tried it MT to MT, try it the other way(FT to FT). The amount of darkening to black or dark whatever colour cast you see is different.

With my CPLs in 3b and 3c, I see almost black in the FT to FT positioning, but only half that darkening if positioned MT to MT .. (FT = female thread, MT = male thread .. if you forgot).

Never made sense to me why it's darker when facing each other with FT together than when facing away from each other with MTs together.
It gets even stranger! This maximum darkening doesn't happen with the filters at 90° to each other, it happens when they're at 45° to each other. Place the markers at 90° and brightness is basically equal to the additive effect of the dark-ish filters.
Place those two markers at close to 45° then tweak, and you see max darkening.

I have no idea what effect the mirror has in wacking out the results, but a single filter on the mirror (to me) is equal to two filters held together with both markers at the same position.

I'd love to try to describe #4 (the next instalment) of mixing a LinPOL and a CPL .. but you'll think I'm having a lend of 'ya, or pulling your legs(but I wouldn't be).
Needless to say it's even more whacked out than the above observations, but much stranger .. and results depend on which filter is in front of which filter.

But this is the only way I can get light blocking at 90° relative orientation to each filter, as they do in the video.
The two CPLs only block out at 45° to each other.

So I can only assume(I only have the one LinPol to play with) that their polariser(s) were Linear types .. which I do vaguely remember do that at 90° .. but this was about a lifetime ago and can't really remember that theory all that well(possibly yr 12 physics experiments).

[Tannin]

I'm a geek! I have proof

I believed you already. You didn't have to provide your proof in your post!

Basically, all polarises are linear types except for weirdo photographic ones. All normal polarisers are linear: sunglasses, LCD screens, industrial ones, you name it.

But what is the go with them working differently different ways around? That's weird. My head hurtz. I'm going to bed!

[arthurking83]

....

But what is the go with them working differently different ways around? That's weird. My head hurtz. I'm going to bed!

For you reading (dis)pleasure .. tomorrow then.

4a if I put the LinPol in front of the CPL, both lined up stacked(MT to FT) I get the darkening when turned to 90° to each other(as per the vid).
4b if i place the CPL in front of the LinPol both lined up the same stacked way(MT-FT) . there is no darkening .. just the browning/blueing colouration effect.

And this goes on for other thread positioning too. The strength of the polarisation effect is determined by the order that they're set as the first filter in the chain.

And all this orderly positioning mucking about business is basically: eye ball | Filter | Filter | light bulb(on ceiling).


One last strange observation I've made over the years with polarisers.
We've all been told over and over again that we have CPL type pols because the mirrors in modern AF systems require it and that these AF systems don't work well with LinPols.

I've predominantly used my LinPol(cost me about $20 about 20years ago for that 77mm size). And I bought a U-bute 77mm ultra slim multi-something'd special doosy $150 bank breaking doodad CPL ... and have never seen any difference in AF, metering nor exposure between the two.
Only smidge difference was that on my UWA Sigma 10-20mm on APS-C, I did see a wee bit more vignetting in dark conditions. But the $150 did supposedly get me an ultra slim, ultra flat glassed UWA sensitive CPL too tho, so at the least I'd liked to have less vignetting.

Even on the bad focusing Tamron 70-200/2.8 .. I've never experienced any issues with focusing and using either polariser.

The next chapter .. #5 I'll do tomorrow morning .. which relates to why I never seen any AF differences between the two pol types .. it' gets even more geeky again!