I have been curious about polarizing filters since I started taking photos, but for some reason I kept them out of my field of interest for a very long time. Although I know that they have a special importance in macro photography, I have waited until today, perhaps because their prices are a bit high.
Polarized glasses have been used in sunglasses for a long time. They relax the eye by preventing reflected light from entering. They serve the same purpose in the camera, blocking the reflected light from, for example, a glass or water surface, allowing us to see through and underneath. They provide bluer skies and higher contrast in landscape photographs.
Linear Polarizer – Circular Polarizer
Without going into technical details, I want to tell the practical difference. In essence, both types of filters do the same job. There is no difference in the results. However, while linear polarizing filters used to be quite sufficient, they have lost their prevalence with the emergence of autofocus bodies. Because autofocus systems do not work with linear polarizing filters. They need a different system called circular polarizing. Circular polarizer filters, abbreviated as CPL, are more expensive than linear ones. If we think only for macro shooting, we can buy second-hand cheap linear polarizer filters. We are not looking for autofocus in macro shooting. But if we want to use it for general purpose, landscape and wildlife photography, we need to choose a CPL type filter.
Again, while I didn’t have much in mind, I decided to get a second hand Marumi DHG 72mm filter that I came across at an affordable price. Marumi brand is known for its quality filters. The DHG surface coating provides an advantage against internal and external reflections. DHG is something like MC coatings on lenses. There is a coating called Super DHG on a newer model, but I didn’t bother with that much.
How to use a polarizing filter
First of all, we need to attach our filter to the filter mount of the lens. Since the CPL filter I had was 72mm, it was too big for my Tamron 90mm macro lens. I had to use a set of filter diameter conversion adapters to reduce the 72mm diameter of the filter to 52mm for my Tamron.
When we attach our filter to the lens, we will see that it has a structure that can rotate around itself. The amount of this rotation, i.e. the angle, is the core of the filter’s working logic. According to the angle at which the light comes in, we rotate the polarizing filter to adjust its angle and cut unwanted reflections. There is a point to be considered here. If the lens we use moves by rotating the front glass while focusing, the polarized angle we set after each focus will be distorted, and we will have to deal with it again. In fact, if we are tracking a moving target, our lens will constantly rotate our filter as it searches for focus and will disrupt our work. For this reason, it is desirable that the lens to be used with a polarizing filter has an “internal focus”, abbreviated IF feature. Thus, the tip of the lens does not rotate while focusing.
In these two photographs, taken with the polarizing filter rotated, the reflection in the leaves of the tree is removed and the color of the sky is darker. This effect provided by the polarizing filter is not something that can be reproduced on a computer, so it deserves special attention.
Polarizing filter in macro photography
Let’s get to the point. What does a polarizing filter do in macro photography?
I hope it won’t be too funny if I say “I don’t know the answer to that question yet either” 🙂
Actually, what I mean is that I haven’t yet decided how necessary it is. After a certain amount of use, I think I will have a clearer opinion, but it is easy to show and interpret the difference already, so let’s move on.
Note: We will get some ideas at the end of the article 🙂
The benefit of polarizing filters is to cut unwanted reflections and glare to create a balanced photograph. These reflections can be a serious problem in flower and insect textures, especially in the shells of insects. Even if we use a large diffuser with a flash, it may not be enough. Again, when using natural light, the glare created by unbalanced light can be annoying. Our aim is to prevent these.
Polarizing film
We can also use a plastic film to do what our polarizing filter does.
But wouldn’t it work the same if we put polarizing film in front of the lens instead of a polarizing filter? Yes, it would. But since polarizing films are made of optically terrible plastic, our photo will come out as if we are looking through frosted glass. That’s why we don’t use it this way.
These plastic films are sold in sheets and they either transmit or block polarized light depending on the angle we use. For example, the glasses with which we watch 3D movies in the cinema work on this principle. There are polarizing filters placed at 90 degrees different angles for each eye. Thus, if the polarized light of one frame of a movie comes in at a zero degree angle and can only enter the right eye, the next polarized frame comes in at a 90 degree angle and can only enter the other eye (the angles are hidden in the light waves). Since these two frames of the right and left eyes are taken by different cameras positioned in the position of the two eyes, we perceive the image in depth. You can also cover ordinary glasses with these cheap polarized films to get 3D glasses.
Why I told you this, one sentence is important: depending on the angle we use, polarizing filters either pass or cut polarized light.
Cross polarizing technique
This is the main topic of this article.
In other words, if we polarize the light first, then we can manipulate it as we want. We can let it in through our lens or not.
If we put polarizing film in front of a light source, our flash, we turn our flash light into polarized light. When this light hits a surface, our insect, if it hits a shiny, reflective part, it reflects back in the same polarized way. So we set the polarizing filter in front of the lens at such an angle that we can completely stop this bright reflection in the filter. Or we can change the angle to partially stop it for a more natural look. The polarized light hitting the non-shiny parts of the insect breaks down and carries the image of the insect to our lens as normal light. This normal light does not interact with our polarizing filter. It enters without interruption.
This application allows us to completely eliminate the bright reflections that bother us.
In articles and tests about the cross polarizing filter, applications on naked flash are usually shown. I consider this an exaggeration because normally we never use naked flash in macro shooting. We do not wash the insect with light using naked flash and burn the photo with blinding bright reflections. There is always a diffuser attached. That’s why in the shots below, I didn’t remove the diffuser from the flash. I also applied polarized film over the diffuser, so I wanted to show the difference in real, not artificial, applications.
I always shoot in raw format, so that even without a polarizing filter there is some compensation for the overly bright areas in the photo, but for this test I’m going to give the photos specifically as they came out of the camera, unaltered.
First let’s prepare our flash, I tape a layer of polarized film on the diffuser. Since the polarized film is a bit small, I covered the edges with dark paper. So all the light coming out of the flash will be polarized, there will be no leakage.
I shot a tiny spider in three different situations, with the same flash power, exposure time and aperture values, and I did not make any corrections. To get it in the cross polarized position, we need to rotate the filter in front of our lens to find the position where it makes a 90 degree angle with the polarized film attached to the flash. This may take a few tries. Once you find it, it will be good to memorize the position of the filter. I don’t know if they all have it, but there is an arrow-shaped position indicator. We see the effect of the polarizing filter in the figure below.
- In the unfiltered shot, despite the diffuser, there is a shiny leaf and a reflection on the spider’s legs that washes out the detail.
- There is some loss of light when a polarizing filter is installed. There is some improvement in reflections but the legs are still reflecting.
- With full cross polarization, all the bright reflections are cut out. But the neutrality is slightly reduced.
We might want to see the three situations a little closer side by side, click to enlarge:
Let’s move on to another example
This time I put a dead wasp on a leaf to compare normal and cross-polarized shots with a diffuser. There was natural light hitting from the opposite direction. I knew that the incoming light would be reflected because it was at an acute angle with the leaf, and that the filter would not be able to prevent this. But I didn’t interfere with this either. When we shoot outdoors, we won’t have a chance to polarize the daylight. Maybe harsh light will come from the right, from the left. Only the light from our flash will be polarized. Here, I wanted it to be similar to the real shooting conditions.
Note: In fact, when the polarizing filter is turned to the appropriate angle, it also softens reflections in natural light. But since we adjust the angle of the filter according to the film in the flash, we cannot soften both lights at the same time.
And again, this time I edited both results in Photoshop, trying to correct the light balances with and without the filter, to see if the polarizing filter really helps. Because, if reflections and glare, which can be disturbing at first glance, can be removed with RAW shooting and computer intervention, then what is the need for a polarizing filter? Nobody uses photographs as they come out of the camera anymore.
We want to see if the polarizing filter will produce a more successful result despite these manipulations.
The cross polarizing filter eliminated the flash reflections on the head, wings and back of the wasp. But in the second picture, the abdomen turned out a bit dark despite the flash I fired twice as strong. The natural light reflection on the leaf from the opposite direction, which I guessed, remained, but the extra glare created by the flash was removed. While in the first photo the wasp is resting in the sun, in the second one it seems to be resting in the shade. The illumination seems to be softer. I must admit that the method worked 🙂
Conclusion
Polarizing filters steal some of the overall lighting. So we have to increase the power of our flash a little bit. Or if we’re using natural light, we’ll need to increase the exposure time.
When using cross polarized, we cut reflections completely in the case of full cross angle. This can sometimes hurt the perception of depth and realism. In fact, it is not something we would want to make a naturally bright object look completely matte. Therefore, when rotating the polarizing filter, it will give a better result to keep the reflections at a semi-cross angle to reduce them to a ratio that will not “burn the photo” or to include some natural light.
I would like to use the cross-polarizing method in the field, outdoors, in a real environment and see the results. I even ordered a second CPL filter in 49mm length immediately because I saw the potential. If you do not have a polarizing filter, I recommend one for both macro and general use.
Update11.Aug.2015
When I got my 49mm polarizing filter, I got rid of the 72mm large diameter one. The smaller and more compact we can be when shooting, the more comfortable we are. Since our lenses are small, 49mm is more suitable for macro.
But even 2 years after the article was published, I still don’t have a clear idea about this. I heard negative comments from many friends, they were uncomfortable with the polarizing filter blocking the light, reducing the clarity.
The cross-polarizing technique lost its meaning for me as I completely abandoned flash photography. I’m more than satisfied with the performance in natural light and there’s still one thing left to try. The use of polarizing filters in natural light.
As you know, we use reflectors and diffuser systems to soften the light in natural light shooting. Sometimes I give them up to save weight, and if it’s cloudy or I’m working in the shade, everything is fine. But sometimes too much light entering from a certain area can produce harsh reflections. In this case, I feel that a polarizing filter can work. If I remember to take my CPL filter one day when I don’t have a diffuser with me, I will be happy to try it and share the results.
