Let’s Talk Filters

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By Steve Russell

A friend of mine requested that I write an article about filters. When he asked I laughed and asked him, “Why don’t you come up with a subject that’s controversial?” At the risk of stepping on the toes of many of our readers, here is my take on filters.

Back when shooting film was the only choice available to photographers, I and probably most serious photographers carried a small arsenal of filters. I had a Hoya circular polarizing filter, two Hoya neutral density filters, two Hoya warming filters and a sizeable set of Cokin filters. While not important to today’s article, I point this out to indicate that I have some experience using various filters and am familiar with what they do.

Today, my filter collection is much smaller and includes a B + W 77mm Circular Polarizing Filter
, a B+W 77mm Neutral Density 3 stop Filter, a B+W 77mm Neutral Density 6 stop Filter, and two B+W 77mm UV Filters.

UV Filters – These filters don’t really do anything but protect the lens primarily from getting scratched. However, here’s the problem; whether you spend $2,000 or $300 dollars on a lens, the light for your photo has to first pass through the filter. If you put a $30 UV filter on a $1,000 lens, you just reduced the potential image quality. If you’re going to use a UV filter, then make sure you buy a really good one with very high quality glass.

There are many photographers that will say that a UV filter is a waste of money and that you should never use one and I’d like to agree 100% with that. Unfortunately, I have had a lens get scratched and the scratch was bad enough that it affected the image quality. For this reason I have the two UV filters that I use under certain circumstances. If I’m at the beach, and especially if the wind is blowing, I use one of the UV filters. If the filter gets sand pitted or scratched I’ll need to replace it, but it won’t cost as much as a new lens. I also use a UV filter if I’m moving around in brush and wooded areas.

In the studio, on the street or other areas where it’s unlikely that the lens could get scratched my lenses always go commando (no filter).

I’ve also heard people suggest that the UV filter helps keep the lens clean and they’d rather clean dust, dirt and finger prints off the filter than the lens. Try keeping the lens cover on the lens when you’re not using it and don’t touch the glass with your fingers.

Circular Polarizer – The polarizing filter has been around long enough that most photographers are familiar with the effects from the filter. Essentially, the polarizing filter reduces glare just like polarized sunglasses reduce glare. However, your sunglasses are linear polarizers and while linear polarizers would work on inexpensive cameras without TTL metering,TTL metering and digital photography require a circular polarizer. A circular polarizer is made of two pieces of glass – a linear polarizer and a Kasemann or wave plate. If you’re interested in the technical information regarding how the two pieces of glass work together you can easily find it on the internet.

Since I was recently asked this question, I’ll answer it as well. The reason the polarizer makes the sky look bluer is that it reduces the glare from the water molecules in the atmosphere and it works best when you’re shooting at a 90 degree angle from the sun. A polarizer also doesn’t work as well with a very wide angle lens. This is because the angle of polarization varies continuously with the angle from the sun and if you’re using very wide angle lenses the degree of polarization will be uneven. Another issue with wide angle lenses, particularly with 28mm or wider, the thickness of the filter may cause vignetting. You can solve that problem by buying a “thin” circular polarizer from either B+W or Heliopan for close to $200 depending on the size of the filter.

Merritt Island NWR Landscape 2
This image demonstrates what happens when you use a polarizing filter with a wide angle lens. Note that the sky of the left side of the image is a much darker blue than on the right side of the image.

A good circular polarizing filter is expensive. If all you want to do with the filter is to make the sky bluer, try adjusting the color of the sky in Photoshop before you spend the money on the filter. Making the sky bluer isn’t the only thing a polarizing filter does. It also reduces the glare coming off water or wet tree leaves or anything else that gives off a glare that would ruin your image.

If you have a circular polarizer, try experimenting with it by shooting at different angles to the sun and see how your filter works. If you have polarized sunglasses, you can look at the sky and tilt you head from side to side to see the effect. Of course, you may want to do that where no one can see you.

Neutral Density Filters – Neutral density filters reduce the amount of light that reaches your camera’s sensor without affecting the color, thus “neutral” density. They’re very useful when you want a slower shutter speed in bright sunlight. If you wanted the water of a waterfall or stream to have that blurred effect when you’re photographing them during the middle hours of the day it’s much easier to accomplish with a neutral density filter. Another way I’ve used them is in street photography when I want my subject or model to be sharp but the people walking by to be blurred. It’s an approach that can result in some very interesting images.

Other Filters - With the exception of some really special effects, I can achieve the same results in Photoshop that I can with filters other than the ones mentioned above. For example, a graduated neutral density filter can be used to darken the sky without changing the exposure of the foreground. However, for me, a graduated neutral density filter is a big waste of money. By using a gradient level in Photoshop, I can produce the same result faster than I can take out a filter and put it on my lens. Plus, I can make it as dark or as light as I want it and I can move it to exactly where I want it and if I don’t like it where it is, I can move it.

Warming filters- Again, I can change the light temperature in seconds by merely moving a slider left and right until I get exactly what I want. I can’t be guaranteed that I will get the exact desired result by using a filter. So, how silly is it to use a filter and then adjust it in Photoshop when I could get the same result without the filter.

There’s nothing wrong with using other filters if you choose, but do yourself a favor and think about what you’re trying to accomplish. If you can do it in Photoshop, why spend the money for filters that are supposed to do the same thing?

Photo Credits:
Merritt Island NWR Landscape by Steve Russell

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  • Johan

    ‘Since I was recently asked this question, I’ll answer it as well. The reason the polarizer makes the sky look bluer is that it reduces the glare from the water molecules in the atmosphere and it works best when you’re shooting at a 90 degree angle from the sun.’

    If that we true, then why doesn’t a polarizer make clouds darker? Clouds contain more water molecules than blue sky… Blue sky is darkened because when sun light hits the atmosphere at an angle, it gets polarized. Clouds scatter sunlight and depolarize it again. That’s why the sky gets darker and clouds do not.

  • Steve Russell

    I don’t have a degree in physics so I can only describe the polarizing effect in lay terms. However, the sky doesn’t get any darker. While a polarizing filter will block some of the light reaching the sensor, correct exposure is still correct exposure. What the filter does is reduce the glare from water molecules suspended in the atmosphere which in turn allows the blue of the sky to appear more saturated. The filter doesn’t change the color or brightness of the sky.

    The filter has the same effect on the clouds but the effect is manifested differently. By reducing the glare of the water vapor suspended in the atmosphere with the polarizing filter, you and the camera are able to see the clouds more clearly and in more detail. The structure of the clouds becomes more apparent. If you study the photograph included with the article you will note that the clouds do appear differently on the left side of the image than they do on the right side. Without the polarizing filter there would be no apparent difference.

  • Johan

    I still disagree. Of course the exposure of the camera compensates for any overall loss of light, so overall the photo doesn’t become darker. That’s not the point. The point is that IF a polarizer would work as you describe, the amount of light that it cuts from clouds would be MORE than the amount of light it cuts from the blue sky, for the simple reason that clouds contain more water molecules than a bright part of the sky. In the photograph, the nett effect would be that the clouds become DARKER relative to the sky when compared to a photograph taken without a filter. In reality it is vice versa, the sky becomes darker (more saturated). The real reason is that light coming from a blue sky is (partially) polarized and light coming from clouds is not (any longer). This polarization is not caused by water molecules, but by oxygen and nitrogen molecules that make up the air. The light becomes polarized when it travels through our atmosphere from the moment it hits the first air molecules. Clouds scatter the light again, and because clouds are relatively close to the observer, that effect is still aparent when the light reaches the camera. See also: http://www.picturecorrect.com/tips/how-a-polarizer-filter-works/

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  • Kim Siebert

    When doing articles like these, and since you are a photography site – it is really important to include examples!

    this was nicely written – but, examples are IMPERATIVE! Please include them!

    And, the one example you did use, wasn’t really that great, and you could barely see a difference.

    Just sayin’

    I’m not being a hater, I’m just trying to help – since your whole purpose here is to help! (and people like me appreciate it)

    thanks for reading – and please don’t ban me!
    :)

    Peace,

    Kim

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