BetterPhoto Q&A
Category: New Answers

Use of filters

Which filter would I use to take pictures of Mtns with snow on them

Thanks in advance for the help

Mitch

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July 08, 2006

The UV filter has been around for a long time. They are constructed of colorless glass. The UV filter stops UV radiation thus preventing it from passing on to the image plane. A good quality UV often appears bluish as this is a transparent overcoat that reduces reflections that normally occur when light rays encounter polished glass. These filters have slight haze cutting ability. Haze is prevalent in distance scenes due to the presence of water vapor which scatters UV light. You can’t see this scatter light as the human eye is incentive to these frequencies. All films are sensitive to UV this scatter records and obscures distance objects. I don’t know about the UV sensitivity of the imaging chip in your camera. Since UV has a short wave length it is more energetic than visible light. Thus you may see some benefit. UV filters are a favored add-on at the camera store. Generally the camera store personnel sell this filter after planting the idea that it protects your precious primary camera lens from scratches and the like. A Skylight filter is a UV filter with a slight pink cast used to warm up distant blue-sky vistas.

The Polarizing filter is a different animal. This is a must have filter for the scenic photographer as it darkens and emphasizes a blue sky. This filter will give breathtaking differences causing white clouds to standout against the sky. Additionally the polarizing filter helps by subduing refection from many shinny surfaces (non-conductors of electricity). It is particularly valuable when photographing glass. This filter allows limited views of objects just under the surface (penetration) in a water scene. For best results you must have the ability to rotate this filter while composing. Stated another way, with the filter mounted, and viewing through the SLR system or viewing the LCD screen, rotate the filter for effect. Because this filter absorbs some light, it is necessary to compensate or under exposure will result. Don’t panics, all modern cameras with through-the-lens metering will automatically handle this chore (filter factor) for you. The Polarizing filter also acts as a UV filter, no need to combine the two.

Enjoy your scenic work!

Alan Marcus
ammarcus@earthlink.net

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July 08, 2006

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July 08, 2006

Light from the sun is non-polarized. As sunlight filters through the atmosphere it strikes surfaces and becomes polarized. The filter darkens sky by removing some of the light polarized by atmospheric scattering. Sky photography is greatly enhanced due a contrast increase. This is probably the most valuable filter the scenic color photographer can possess.

The filter can be thought of as:
A glass or plastic window with fine lines ruled on its surface. These lines are spaced extremely close together and are parallel to each other. The filter functions like a picket fence. Think of a picket fence with a jump rope transversing through a gap in a pair of picket. You can pluck the rope like a banjo string. However, the sting can only be plucked (vibrated) in one direction, up and down; a sideways pluck fails as the rope will strike the pickets and vibration will be arrested. All light waves are vibrating like the plucked rope. Un-polarized light is vibrating in all directions i.e. up-down left-right or at all other orientations. Polarized light is vibrating only is a single plane (one direction only). Light striking non-conductive surface’s is cause to become polarized so that it vibrates mainly in one plane. The filter stops all rays except those that are aligned with its grid lines.

These filters are manufactured in two (2) types.
Linear as described as above with a grid line like structure parallel ruled.
Circular which exactly the same but with an added thin layer that causes the polarized light rays to be polarized again thus the emerging ray is caused to take on a circularly alignment. This negates the initial alignment. Both photographically produce about the same effect.

There are myths and misunderstandings about these filters. One myth is: You must use the circular type with a digital camera. The facts are different. It makes no difference to the camera which is used with two (2) caveats. Some auto-focusing systems and some through the lens metering systems (digital and non-digital) utilize a polarizing filter in their design. In these cases only the circular type will not interfere with the camera’s proper action.

Alan Marcus
ammarcus@earthlink.net

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July 08, 2006