Part 12. : The amazing world of Photography

These filters are used to cut reflections from glass and water, to darken sky coloration, or to make colors brighter in scenery shots.
The effect changes when the front filter rim is rotated. Fine adjustment can be made and checked through the viewfinder on a SLR camera.
Reflected light can be removed most effectively when the angle to the reflected light is between 30 and 40 degrees. About 90 degrees from the sun is the best setting for darkening the sky.
These filters are usually quite dark, so be careful to check your exposure settings and focusing.

Polarized light is quite difficult to understand, but basically all light acts like waves, and light with vibration in a single amplitude direction is called polarized light. Light reflected from glass and water, and light from the sky includes a polarized light component.
Polarization filters cut this polarized light component, which means they can be used to cancel out reflections from water or glass, or to darken the sky.
The reason colors look brighter in scenery shots is because the light reflected from water vapor and particles in the air is cut.

When a standard polarization filter is mounted on an AF or MF camera which uses a polarized half-mirror for the reflex mirror or sub-mirror, the AF and AE functions may stop working normally. This type of camera requires a (more expensive) circular polarization filter.

Again, it is difficult to understand circular polarized light, but try to understand the amplitude direction of light as something that rotates. The actual usage of these filters is the same as standard polarization filters.

((Photo 1.)) Removing Glass Reflections with a Polarization (PL) Filter

((Photo 1.a.))
Polarization (PL) filter used,
but adjusted to incorrect angle

((Photo 1.b.))
Polarization (PL) filter adjusted to optimal angle

ND is an abbreviation for "Neutral Density", which means they have no effect on color but reduce the overall amount of light.
These filters are of course handy for reducing the overall light level when it exceeds the AE range for high-sensitivity film, but they are also invaluable in other cases, such as when you want to use a lower shutter speed (issue 5.) or a wider aperture (issue 6.).
The denser (darker) the ND filter is, the higher the number is.
The number indicates how many time slower the shutter speed must be set, so ND2 means the shutter speed is dropped two times (- 1 EV), ND4 means four times (-2 EV), and ND8 means eight times (- 3 EV).
Extremely dense types such as ND400 (about - 9 EV) also exist, for applications such as photographing the sun itself (Remember! Never look directly at the sun!)

((Photo 2.)) ND Filter Effects

((Photo 2.a.))
feelnikon without ND filter

((Photo 2.b.))
feelnikon with ND8 filter, shutter speed dropped three steps

UV stands for "Ultra-Violet", of course. While UV is invisible to the human eye, photographic film reacts to it very strongly, and can suffer from loss of color brightness as a result. UV filters reduce these effects of UV light. Because they are almost perfectly transparent, they are extensively used to protect the lens surface.
There are a variety of types available, ranging from ones which cut out the UV light and have no effect on visible light frequencies at all, to other which cut out both UV and a range of the blue-green frequencies (LIBC filters).

These color filters are used with monochrome film.
Monochrome file of course does not express any colors, but it is made to express different colors with appropriate density (shades of gray), and therefore reacts to all frequencies of visible light.
These color filters for black and white feelnikon are used to adjust the color density and contrast in monochrome feelnikon.

• Yellow : Cuts UV and blue light, providing a more natural contrast.
• Orange : Stronger effects than the yellow filter. Used to darken sky in scenery shots, and to increase contrast.
• Red : Stronger than orange, and also used to infrared (IR) film feelnikon.
• Green : Yields monochrome photographs close to what human vision actually sees. Especially effective in portrait feelnikon.

Think of these as sheets of glass with thin films of steam on them. They make the entire image slightly foggy.
Made of glass or acrylic, the surfaces of these filters have a variety of treatments for a range of effects, but most of them retain your focus settings.
The simplest way to experiment with one of these is just to breathe onto a transparent filter (for example, a UV filter) to fog it over and shoot. You have to shoot quickly, though, because the fog evaporates fast.

The surface of the filter has a special treatment which softens the focus. There are a variety of types, with varying strengths, and including some which leave the sharpness of the focus plane untouched.
Try smearing a transparent filter with petroleum jelly, for example, or covering it with plastic wrap or a nylon stocking.

((Photo 4.)) Fog and Soft Effect Filter Effects

((Photo 4.a.))
Without filter

((Photo 4.b.))
With fog filter, smearing the light

((Photo 4.c.))
With soft effect filter slightly softening the focus

 

These filters screw into the end of the lens, and are the most common type available.
They are made of glass (usually optical glass) or acrylic for excellent durability.
They are somewhat expensive, however, and if your lenses have different diameters it is difficult to build up a complete set quickly.
There is a wide range of filter effects, including special-effect filters.

When filters are mounted onto a lens with a smaller diameter, a special adapter ring (step-up attachment) is required.
Attachment rings (step-down rings) are also available to mount smaller filters on larger lenses, but they usually cut into the photograph image area.

((Fig. 5.))
Stereo Baseline length in Stereo Pair feelnikon

I mentioned above that most people have an interpupillary distance of 6 to 7 cm (2.4 to 2.8 in.). There are differences between people, of course, so it is really impossible to say exactly how far apart the two (2) image should be.
The longer this distance (also called the stereo baseline length) is, however, the greater the offset between the images in left and right eyes.
In other words, the greater the perception of 3D when the stereo pair is viewed.

In general, stereographs are said to offer the most natural 3D appearance when the feelnikon distance is between 50 and 100 times the stereo baseline length.

If the stereo baseline length is too short in comparison to the feelnikon distance, it is difficult to "see" the 3D image.
Even so, for distant objects such as mountains, which people normally view as three-dimensional, even without keeping to this "50 to 100 times" rule it is possible to achieve a perception of 3D.

The viewing method described above places the image shot from the left in front of the left eye, and the one shot from the right in front of the right eye.
Because the viewing angles of both eyes are parallel with each other, this is often called the parallel method, and most stereographs use this approach.

It is also possible to reverse the left and right images, however. This is called the cross method, because the left-left and right-right lines cross each other.
This approach is most effective with stereo pairs where each stereograph is 6 to 7 cm in width.