Polarizer

[iceberg]

Hi
newbie here.. bought a circular polarizer... faced some difficulty in using it... coz when i rotate the outer ring.. i don't see difference through the viewfinder... any advices on this?

[iz_k]

cos it's circular?

[iceberg]

so how to actually use it then?

[iz_k]

Originally Posted by iceberg Hi newbie here.. bought a circular polarizer... faced some difficulty in using it... coz when i rotate the outer ring.. i don't see difference through the viewfinder... any advices on this?

Hmm... i dunno if i'm qualified to explain here. But basically there's 2 types of polarizing filters, circular and linear... most(not all) of the time, linear polarizers are used on a manual focus. By rotating a linear polarizer you can progressively prevent the polarized components of light passing through, while allowing normal light to pass through unaffected.

As you've said, what you got is a circular polarizer. Don't have to turn the ring to adjust the polarizer of the glass. Circular Polarizer has linear polarizer construction plus a built-in "Wave Retardant" to ensure proper exposure. The linear element polarizes the light, and the wave retardant de-polarizes it, and then your camera metering unit will polarize it again for proper exposure. Usually results in underexposure...

Polarizers have little or no effect when they are used in the same direction as the light source. So try using it ard 90 deg from the sun if shooting outdoors.

[wacko]

i think iz_k has it all wrong about circular polarizers. you still have to turn the polarizer, be it linear or circular, to obtain the optimum polarizing effect. your orientation to the light source does matter as to the extent of the maximum polarizing effect. that's about all that i am sure about, think there are some articles on the internet which may interest you if you want to understand the effect further.

[darkness]

I hope when you mean "viewfinder", you are referring to the viewfinder of an SLR, where what you see is thru what the lens sees (i.e., thru the polariser). If you are using a normal digital camera without EVF, the viewfinder doesn't see what the lens see, and you will need to compose using the LCD screen in order to see the effect.

Also, the direction of the light may or may not affect the scene thru the polariser. The most effective angle for the polariser to work is 90 degrees, as iz_k has pointed out.

[Zerstorer]

Linear polarizors and Cir-pol work in the same way.
The only diff is that Cir-pol has another quarter wave plate that redistributes the light again to make it compatible with AF sensors.

[mervlam]

if you are really interested on how polarisers (both linear and circular) work, just go to the library at either NUS or NTU, and pick a book that talks about Optical Physics or ElectroMagnetic Waves.

alternatively, do a search on a Internet Search engine.

Just finished a module on Electromagnetics... me don't want to spew "garbage" here.

[mervlam]

Originally Posted by iz_k Hmm... i dunno if i'm qualified to explain here. But basically there's 2 types of polarizing filters, circular and linear... most(not all) of the time, linear polarizers are used on a manual focus. By rotating a linear polarizer you can progressively prevent the polarized components of light passing through, while allowing normal light to pass through unaffected. As you've said, what you got is a circular polarizer. Don't have to turn the ring to adjust the polarizer of the glass. Circular Polarizer has linear polarizer construction plus a built-in "Wave Retardant" to ensure proper exposure. The linear element polarizes the light, and the wave retardant de-polarizes it, and then your camera metering unit will polarize it again for proper exposure. Usually results in underexposure... Polarizers have little or no effect when they are used in the same direction as the light source. So try using it ard 90 deg from the sun if shooting outdoors.

definately wrong, unfortunately... guess u got to go read up on polarisers... it may be a simple piece of equipment, but there's lots of background stuff u got to know in order to utilize it correctly.

*cheem stuff to explain why it's named linear or circular*

linear polariser: it's linear because the electrical or magnetic component of the light wave oscillates in a plane after it passes thru the polarising material.

circular polariser: circular because the electrical or magnetic component of the light wave will rotate 360 degrees in period T around the axis of propagation of the light wave (like a spiral) after it passes thru the polarising materal and quarter wave retardant.

[songandesther]

Originally Posted by iceberg Hi newbie here.. bought a circular polarizer... faced some difficulty in using it... coz when i rotate the outer ring.. i don't see difference through the viewfinder... any advices on this?

The easiest way to test out is to look for something that reflects light, for example your computer screen when you look from the bottom at an angle. Then slowly turn the outer ring of the polariser while looking at the reflection. You will see that at some point while you turn, the reflection will weaken or totally go away.

Another way is to look at the sky at a direction 90% to the sun on a bright sunny cloudless day. As you turn the outer ring you can see the blue sky darkens.

[iz_k]

Gee, thanks guys for explaining. Maybe i read from the wrong website...
BTW, can anybody explain to me why my circular polarizer doesn't have an outer ring? it's a 72mm bought from CP. i threaded in it all the way and it stays there like uv filter. no outer ring, inner ring.

[wacko]

Originally Posted by iz_k Gee, thanks guys for explaining. Maybe i read from the wrong website... BTW, can anybody explain to me why my circular polarizer doesn't have an outer ring? it's a 72mm bought from CP. i threaded in it all the way and it stays there like uv filter. no outer ring, inner ring.

heh, somehow i think perhaps you have been conned?

[loupgarou]

is light off a mirror polarised? heh

[iceberg]

heh.. managed to see the effects of polarizer after a photoshoot... thanx thanx

[mervlam]

Originally Posted by loupgarou is light off a mirror polarised? heh

no.... light reflected off metallic surfaces is not polarised

[HelmetBox]

Originally Posted by mervlam no.... light reflected off metallic surfaces is not polarised

Light reflected can be completely polarized, partially or not at all. This will depend on the angle of incidence (angle of incident beam to the normal).

If light is not reflected perpendicular to the surface, there will always be a partial polarization of some extent.

Hope this helps.

[mervlam]

Originally Posted by HelmetBox Light reflected can be completely polarized, partially or not at all. This will depend on the angle of incidence (angle of incident beam to the normal). If light is not reflected perpendicular to the surface, there will always be a partial polarization of some extent. Hope this helps.

yes... but light reflected off METALLIC surfaces can never be completely polarised

[HelmetBox]

Originally Posted by mervlam yes... but light reflected off METALLIC surfaces can never be completely polarised

yes, light off metallic surfaces will not completely polarise.