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Information about polarizing and zero density filters

You talked about filters in general without some important details, especially about the (Neutral density) filter and the (Polarizing) filter.
Please provide more clarification on the importance of these two candidates and the method of working with them, and let it be at length.
Abdel Wahid More
Jordan

Zero density (Neutral density), as it is clear from the name, means that less light is transmitted
To the movie, if you want to work with a slow shutter speed to blur a fast-moving athlete and suggest strength and movement in an engraving way, then with (Tri-X) film under bright sunlight, the slowest speed is
You can set it up - even with a lens, as narrow as f/22 - to 1/125 or 1/250, and that's subtle enough to blur a race car.
The density filter allows you to narrow the lens down to f/32 and at very small apertures, you can work at shutter speeds as slow as 1/2, and still get a correct exposure. This, and with a slow movie. You can leave the shutter open for several seconds, send moving cars disappearing from a city street, or turn a rushing stream of water into a mist of air.

Neutral density filters are sold in a series of densities, the weakest commonly used of which reduces light to half its filterless luster, a one-stop reduction.
However, the most useful filters are denser than this, so the filter with no density of 0.9 reduces the light by three stops.
And if you are determined to buy one density filter, it is the best; The stronger filters are not usually available in stock, but you can get them by special order. The German company BW probably manufactures the most comprehensive series of glass filters, and Kodak sells a very wide range of these filters as gels.

As for the high density filters (such as 2.0 ND), which reduces the light by almost seven stops, it looks almost black. It is ideal for landscape photography, and allows not only flowing water, but windblown trees, jungles, grasses, and grain fields to be blurred.
When using a filter with no density and somewhat blurred, there is no need to take special precautions, because the viewfinder in the camera only dims a little, which means that you can focus and shape the image in the usual way.
The TTL exposure meter in the camera will take over the task of making the necessary exposure.
The denser filters need more care.
Focus first, then install the filter, because if you do not act in this manner, the image will be very dark in the viewfinder, so that the focus will be difficult and inaccurate. Take a photometer reading before installing the filter, because you
It may be difficult to see the needle of the meter or scale while the viewfinder is very dark.
If the meter indicates an exposure of 1 second or longer, your photos will be bracketed. deliberately erring on the generous side of the correct exposure.” This is necessary because the film loses some of its sensitivity to light when the exposure level is low. For example, if the timer indicates five times, make the exposures at five, ten, and twenty seconds.

polarizing filters:
Polarizing filters have very noticeable advantages. Although they appear gray, DN filters can be used to optionally darken certain areas of a subject, or to reduce reflections from glass, paint, or water.

Polarizing filters consist of very fine gratings made of long, thin crystals, all running parallel to each other. And by rotating the filter in its holder, you can change the orientation of these crystals, so that they block light that is polarized in a certain plane. If you use Polaroid sunglasses to drive a car, you will be familiar with this principle already - that the surface of the road causes light to be polarized in a horizontal plane, and the crystals in the lenses of the polarized light - although in practice, you do not need information about Theory even makes polarizing filters work for you.

The most dramatic feature of one of these filters is its ability to remove reflections. For example, if you are photographing a shop front, and the reflections in the glass obscure the exhibits behind it, you can remove these reflections with a polarizing filter.
However, in order to do this properly, you should not look at the window directly, take a perverted view instead, and the reason is that the polarizing filter removes
Reflections are most effective while the camera is at an angle of 30 degrees with the flat glass.

However, you do not need to make an accurate measurement of the angle if you adopt the following simple method: Stand at an angle with the front, and rotate the polarizing filter until the reflections are at their lowest, then rotate the camera so that the camera axis is at a steeper angle with the glass. You will find that there is an extreme angle at which it occurs The filter completely eliminates reflected light.

Since the standard lens on a 35mm camera has an angle of approximately 40 degrees across the width of the frame, reflections will be eliminated in just one area of ​​the field of view, not across the entire image. However, with a wide-angle lens, the unevenness of the reflection can be so noticeable that a clear pit may appear in the middle of the surface covered by the reflection. A high focal length lens, on the other hand, has a narrow angle of view that applies within the small area from which the reflections have been removed. .
To make the most of a polarizing filter to reduce reflections from the glass, mount it on a lens. Telephoto.
The method to be taken to remove reflections from the water is very similar to what we preferred, except that the maximum angle of water is slightly steeper - about 37 degrees - which means that a polarizing filter will work best if you are able to look down at the water sheet from above. At a bridge or a high bank.
Wind is another hindering element. Because it pushes the water into turbulence, causing ripples. And since they face the camera at varying angles, the energy is reduced
Reflection in a polarizing transfer filter on a windy day.
In addition to water and glass. Polarizing filters will remove reflections from all
Other shiny materials, except for exposed metal such as chrome plated, silver, gold, or crumpled iron. However, if the metal is coated, as is the case on the body of a car, the polarizing filter will do its job as usual.
As for the reflections of light sources such as the sun, the polarizing filter does not remove them completely, because they are very bright.
At the maximum angle of action of the polarizing filter, the reflected light source appears much darker. It may pick up a color tinge.
Such are the cheap polarizing filters, emitting bright, deep purple colours. Attractive though this may sound, it really stands up to objections, like bright purple ripples in a romantic pond surrounded by trees! As for the higher-priced polarizing filters, they usually leave behind an image of reflected radiance with no color, otherwise the image will be brown as the color of the earth.

Color reinforcement:
On a sunny day, while the sky is blue, you can use a polarizing filter to strengthen the color in the sky, and to make vegetation such as grass and green leaves look richer. Here, as before, it is sufficient to rotate the filter while looking through the viewfinder. You should easily see when the colors are at their brightest, and what you see is what the camera records.
There is a maximum angle for dimming the sky, and there is a similar angle for reflections. These lie at 90 degrees from the sun, which means at midday, the sky will be darker than it is at the horizon;

While during sunrise and sunset, the area that the polarizing filter will darken most of what it does is located in a wide strip of the sky. At different angles with the sun, then pick up the location that gives the best effect.
Avoid using polarizing filters with ultra-wide-angle lenses, since these will show a very wide view of the sky, giving off a mottled appearance of deep blue shades within a lighter blue.

Remember also that a polarizing filter will only darken a blue sky. When the sun is shining but the sky is white, the polarizing filter will not make the sky bluer, although it will still deepen the greenness of the plants in the scene. It is worth noting that polarizing filters absorb a large amount of light, regardless regardless of its destination. A typical figure for this absorption is 1/3 a stop, although cheaper filters may absorb more. It is true that the TTL counter in the camera will compensate for any light being absorbed, and as you turn the filter to remove reflections or darken the sky, you may see the counter needle moving in the viewfinder, or the LED reading changing.

If the change reaches half a stop or more, take note of the minimum and maximum readings, then set the camera meter to operate - manual. If you use the filter to remove reflections, put the minimum reading or the widest aperture .. but if the filter works to darken the colors. Put the large reading, the one that indicates the fastest shutter speed or the smallest aperture ⏹