Examples of optical filters

Let's look at some related examples. Figure 7. Figure A in13 is a photo without a filter. Figure b is a photo taken with a red filter. Comparing Figure A and Figure B, it is not difficult to find that the red roses in Figure B are brighter, some petals are even whiter, and the surrounding green leaves are darker. The result is just the opposite of Figure B, with brighter green leaves and darker red roses.

These photos show how to use filters to separate colors and make them contrast and highlight a certain color.

So, when is it appropriate to use a filter to separate a color from a black-and-white photo? There are many such situations. For example, when taking landscape photos, the green filter is very useful because it can deepen the tone of the sky and dilute the tone of the surrounding vegetation-enhance the contrast between them.

When shooting autumn scenery, you can use a red filter or orange leaves to brighten the photo and make the blue sky look good.

In architectural photography, photographers often use red filters. Adding red filters can increase the tone of dark blue sky and highlight the buildings they shoot more prominently.

What would a red filter look like for portrait photography? I can tell you for sure that this is a bad idea. Pink skin looks bleached, red mouth is surprisingly pale, and good people become ghosts. We may all have had this experience: standing on a hill and staring at the beautiful fields in front of us, with rolling mountains in the distance and cumulus clouds floating in the blue sky like white waves. The scenery is so beautiful and charming. I couldn't help taking out my portable camera and shooting this amazing scenery with black and white film. But it's a pity: in the last photo, only light gray clouds are set off under the same light gray sky, lacking details.

This is a failed photo, which is quite different from the charming scenery. However, how did the intoxicating scenery we saw become like this? Why are the white clouds in the photo not as bright and prominent as those in the real scene? The reason is that film and human eyes treat colors differently.

As we know, black-and-white photos are composed of different shades of black and white, from pure white, light gray, dark gray, black gray to black.

When shooting the blue sky-white clouds scene as mentioned above, we should use a filter that can deepen the blue sky tone. If the blue sky in the photo is a dark gray tone, then the white clouds will form a contrast.

It should be noted that the white clouds in black and white photos should not be reproduced as pure white tones, and it is best to have light gray tones. After adding another filter, the tone of the white clouds is basically unchanged, and the white clouds are kept light gray. What we have to do is to deepen the color of the blue sky, thus highlighting the white clouds.

Without a filter, what kind of effect will there be when shooting a blue sky-white clouds scene without a filter? See fig. 7. 14, where fig. a is the result without filter. On black and white film, the dark blue sky is light gray and the white clouds are light gray. Results: There was no comparison. The blue sky and white clouds set each other off, showing a light gray tone.

Yellow filter If you use a yellow filter when shooting, you will find that the blue sky has a dark gray tone. But consider how to choose the most suitable yellow filter. It depends on how deep we want the blue sky. The darker the filter color, the darker the blue sky will appear in the photo. Figure B is a photo taken after using the yellow filter. Figure c uses a dark yellow filter. You can see the photos taken by the deep yellow filter, and the gray tone of the blue sky is deeper.

Green filter In order to get a darker gray sky than the yellow filter, we can choose the green filter. The most common green filter used by professional photographers is the light green filter of NO. 1 1. The photo shown in Figure D was taken with a light green filter 1 1. Among them, the blue sky is reproduced as a deeper gray tone, which highlights the white clouds more obviously.

Red Filter With the red filter, you can shoot the sky near black. The most commonly used red filter number is 25. The photos taken with this filter are shown in Figure E. ..

Why not use a filter as dark as possible?

We may think: our goal is to deepen the gray tone of the blue sky, so why not use the red filter to get the sky with the deepest gray tone? The answer is obvious, that is, deepening the tone of the sky is only one of all purposes, not the only purpose. More generally, there are many objects in the scene, such as trees, flowers, people, livestock and buildings. If we use the red hue, we may change the hue of other objects accordingly, resulting in unsatisfactory results.

When we appreciate a black-and-white photo, we are always used to a certain standard tone. For example, the blue sky is usually gray, and it should not be black under normal circumstances; Lawn is usually a medium gray tone, which should not be white or black under normal circumstances, and so on.

So we'd better choose a filter whose color is not too dark, so as to highlight the target we want. If deepening the color of the blue sky to highlight the white clouds is just our purpose, then we should choose a light yellow filter. On the other hand, if the sky is the main part of the photo and our main goal is to highlight the white clouds in sharp contrast, it is more appropriate to choose a darker color filter.

How to choose a filter to achieve the best effect? If we have all kinds of filters, then don't be stingy with that little film money and a few minutes. We should do more experiments and try different filters. Next time you meet charming blue sky and white clouds, put on black and white film and record the filter you use. The next thing to do is to print out the photos and compare the results. There is no better way for us to get familiar with the performance of various filters as soon as possible. We have discussed before how the defogging filter penetrates the mist when shooting color film. What should I do with black and white photography? We are also confident enough, because the fog lights can be removed by using the color filter, and the light reflected by the subject can be projected onto the film through the filter.

Fog is actually composed of some particles that can scatter the sky light. What color is the skylight? It is blue. In other words, fog scatters blue light. In order to see the scenery clearly through the mist, these blue rays should be removed. So how do we do this? Blue light can be removed by using a filter. The blue filter only allows blue light to pass through. Therefore, the use of blue filters cannot achieve this goal. However, neither the yellow filter nor the red filter allows blue light to pass through, so it is more appropriate to use these two filters. Is it okay to use a green filter? Need to remind everyone that green light is a mixture of blue light and yellow light. That is to say, although the green filter will not let all blue light pass through, some blue light can pass through.

So what kind of filter should I choose? In Figure 7. 15, we can see the results obtained by using different filters. If it is medium fog, a green filter or a yellow filter is enough. If you encounter dense fog, it will be better to use a red filter.

What should I do if I encounter an impenetrable fog? I'm sorry to tell you that any filter is useless at this time. If there is no light from a distant object, the filter can't see the target. Therefore, only when the fog is not too heavy, that is, when we think it is normal, the filter can play its due role.