Photographic 'Circular Polarisers': what are they?

  • Thread starter sophiecentaur
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In summary, circular polarizers are a linear polarizer followed by a quarter wave plate to generate circular polarization again. They are marketed by Hoya, for example, and are claimed to have a similar effect to rotatable linear polarizers.
  • #1
sophiecentaur
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For years, I have been using a rotatable linear polariser to improve landscape photographs.
They work very well at reducing the reflections from water, reduce the effects of haze and generally sex-up pictures.
I thought the reason was quite simply that they reject on particular polarisation plane.
The latest thing, on Photo Forums, seems to be the 'Circular Polariser', which is claimed to have a similar effect and which is marketed by Hoya, for example. These filters are also rotatable.
I queried what they did and was told that they do the same enhancement of landscape pictures and that one could be used in conjunction with linear polariser to get cancellation (as with crossed polaroids) at a particular angle.

You can produce circularly polarised light fairly easily with a quarter wave plate system but I don't see how that can select / reject one particular polarisation - because the E vector rotates to every angular value.

Am I missing something here? Is it just an advertiser's way of renaming a Round, Rotatable Polariser as a Circular Polariser or is there some genuine effect here?
 
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  • #2
Circular polarizer filters are a linear polarizer (to select one polarization) followed by a quarter wave plate to generate circular polarization again.
The only reason to use a circular is if you have a camera where the autofocus uses a beam splitter to take off part of the light (which is pretty much all of them)
 
  • #3
Thanks. That make sense.
So, yet again, I must dig deep in my pockets!
 
  • #4
I'd be surprised if those circular polarizers work that well- the polarizer may be very achromatic, but the retarder is likely not. In addition, the acceptance angle of a retarder is usually small. At least, the achromatic retarders I have seen (Fresnel rhombs) are very large and have small aceptance angles.
 
  • #5
I just checked. My pentax k10 focusses perfectly well with an old fashioned polariser. So I just don't care! So there, Mr. Hoya.
 

FAQ: Photographic 'Circular Polarisers': what are they?

1. What is a photographic 'circular polariser'?

A photographic 'circular polariser' is a type of filter that is used in photography to reduce glare and reflections from non-metallic surfaces, such as water or glass. It works by selectively allowing light waves that are vibrating in a specific direction to pass through the filter, while blocking light waves that are vibrating in other directions.

2. How does a circular polariser differ from a regular polariser?

Unlike a regular polariser, a circular polariser is designed specifically for use with modern autofocus cameras. It contains a quarter-wave plate that converts the linearly polarised light from the filter into circularly polarised light, which can be detected by the camera's autofocus and metering systems.

3. What are the benefits of using a circular polariser in photography?

A circular polariser can enhance the overall quality of a photograph by reducing glare and reflections, increasing contrast and saturation, and improving the overall clarity of the image. It can also be used to darken the sky in landscape photography and to reduce the appearance of water or glass surfaces.

4. Are there any drawbacks to using a circular polariser?

One potential drawback of using a circular polariser is that it can reduce the amount of light entering the camera, resulting in longer exposure times. This can be compensated for by adjusting the camera's shutter speed or ISO setting. Additionally, using a polariser can sometimes create an uneven or unnatural appearance in the sky if not used properly.

5. How do I use a circular polariser in my photography?

To use a circular polariser, simply screw it onto the front of your camera lens. You can then rotate the filter to adjust the intensity of the effect. It's important to note that the effectiveness of the polariser will vary depending on the angle of the light source, so you may need to experiment with different angles to achieve the desired effect. Additionally, it's best to use a polariser on a sunny day with the sun at a 90-degree angle to the subject for the best results.

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