Cir-Polarizing Filter

[Johnc]

Recently purchased a Cir-Polarizing Filter (Hoya) and notice that there is a white marking on the outer rim that can rotate a full circle.
Is this significant?
Are there 2 lens and why would the outer rim rotate?
Have taken some pics with white mark in different positions and their appears to be no difference, but would just to check.
Thanks
John

[PhotoTraveler]

You need to go outside with it and point in different directions, you will see the difference as you rotate it.

Polarizers need to rotate so you can line them up correctly to get the effect desired, it could be blue skies, or removing glare from water, what ever.

The marks are for reference, I don't use them, but if I remember correctly you point the dot at the sun. But normally you just turn it while looking through the view finder.

You will find it only works if you are pointing 90 degrees to the sun. It has no effect if you point head on to the sun, or 180 degrees from the sun.

[PhotoTraveler]

Another fun thing is hold the filter between you and your LCD (I'm assuming you have an LCD monitor). Hold it as it would be on your camera (threads towards your eyes). Rotate the filter. You will see a transition from clear to black coming through the filter. If you reverse it (threads towards screen), you will just see a tint change.

In my case, white dot at 12 o'clock is clear, at 3 o'clock it's black.

[Johnc]

Thanks guys- I have learned something.
Now to play and experiment.
Much appreciated
John

[KevinBarrett]

I should point out that the polarizing filter works its magic only with natural daylight. It will darken blue skies, remove reflections from glass and water outdoors, and do trippy things to metal-flake auto paint, but it will not remove reflections of light from artificial light sources.

[Javelin]

, and do trippy things to metal-flake auto paint, but it will not remove reflections of light from artificial light sources.

Didn't know about the flake in the paint. but i'm pretty sure they will reduce reflections in glass like windows and display cases no matter the light source.

I always remember the fibreglass boats they made in the 70's and 80's with so much shiny any heavy flake under the clear gel I couln't look at it directly without going cross eyed.

[David Kilpatrick]

Kevin, you are wrong about artificial light sources. Polarisers are used in the studio with tungsten and flash alike, to remove reflections from wood and glass or some plastics. The effect is independent of the source of light.

Polarisers will remove or accentuate specular reflections only, not mirror reflections. Specular reflections are found on many sheeny or glossy surfaces - polished leather, laquered wood, human skin and hair, foliage especially waxy or wet leaves; the surface of water; glassware and windows; autopolish and paintwork; paper, ink, etc. Anything you can tilt and get a sheen from. They are maximum on most surfaces when the angle of incident light is around 40 degrees and the viewing angle is diametrically opposed.

Mirror reflections are found in mirrors (silvered glass), polished metal, chromium plating on plastic. Mirror reflections do not change intensity as you angle the surface.

Polarisers will darken skies (this is a result of the effect of the atmosphere on sunlight - probably what you were thinking of) but all other colour intensifying is a result of cutting through surface sheen (specular reflection, however diffuse). They will also darken other polarising substances/media such as stressed glass (car windshields, in a pattern); LCD screens etc; polaroid sunglasses; clear plastics - polystyrene mainly; dichroic crystals or crystalline layers.Try drying some soda or salt, other household stuff, on a glass sheet - transilluminate, shoot close up with a polarizer under the glass and another on top, rotate for effect. Crossed linear polarisers are used for darkfield photomicrography this way.

David

[Andy B]

While riding a train from Denali to Anchorage last year on an overcast day, I tried using a circular polarizer on my Sony 18-250 while taking scenic shots through the tinted train window. I thought this would cut down on the window reflections. However, when I reviewed these images later on my computer, many of them had large green and purple streaks running across the image. This was particularly noticeable in river scenes. Any idea what caused these green and purple streaks? Could it have been the circular polarizer, or the tinted train windows, or the combination of both? Would I have been better off not using the CP? I've never encountered this problem shooting through tour bus windows.

Andy

[KevinBarrett]

Ah, thank you for that clarification, DK.

[David Kilpatrick]

While riding a train from Denali to Anchorage last year on an overcast day, I tried using a circular polarizer on my Sony 18-250 while taking scenic shots through the tinted train window. I thought this would cut down on the window reflections. However, when I reviewed these images later on my computer, many of them had large green and purple streaks running across the image. This was particularly noticeable in river scenes. Any idea what caused these green and purple streaks? Could it have been the circular polarizer, or the tinted train windows, or the combination of both? Would I have been better off not using the CP? I've never encountered this problem shooting through tour bus windows.

Andy

Toughened glass. The glass has a plastic film between layers. Same as a car windscreen with laminated glass. Try a polariser through a car windshield and you will get the same effect, but through the side windows of the car it may not (different glass). All you did by adding a polariser to the tinted windows was reduce the light still further, making a poor photographic situation even worse - plus the unwanted effects of the polariser on the stressed toughened glass.

David

[braeside]

David, I had read about fitting polarising filters over studio lights so that reflections of the light can be more completely eliminated from objects such as paintings by using an on lens polarising filter, is that a technique that is much used?

[David Kilpatrick]

It's used by anyone who has shelled out for the large polarisers and the necessary holder!

Typical costs and fragile nature of the filters put people off. I incinerated a couple of £50 a sheet polarisers in the 1980s. I don't own one now, but I still have a bundle of other coloured gels which survived, some a bit melted - then new heatproof ones appeared in the late 80s.

I think the widespread use of softboxes instead of direct small sources ended the popularity of pols on lights except for very special purpose.

David