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Camera Lens Filters for Photography

In this article we’re going to talk about the world of lens filters, and I’m not referring to the types of filters you see in Photoshop, but the “real deal” glass ones you screw on your lens.  In this day and age with all you can do in post-processing on the computer, many photographers wonder if there is still a need for filters.  I can assure you, there is…

The good news is that there are really only two kinds of filters you “need” to know about.  Once you understand them, how they work, and what they’re used for, those two kinds will cover 90% of your filter needs.  They are the Polarizer and the Neutral Density filter.  Toward the end of this article, I’ll briefly touch upon some of the other kinds of filters too.

Firstly, what is a filter?  It’s just a piece of glass that you attach to your lens that has various effects on the picture you’re taking.  They can help with making colors brighter, or cutting out haze on hazy days, fixing bright skies, etc.  One quick note – I say “glass” here, but they’re not always actual glass – sometimes they’re high-grade plastic or some other material, but for our purposes, we’ll just call it glass…

So before we talk about all the ways to physically attach a filter and how to actually “use” them, let’s jump right in and talk about the magic that is the polarizer.  A good polarizer may be the most important filter you buy, and is usually the first.  It’s important for two reasons -- #1, polarizers can have a dramatic effect on your photos that can make them look much better and #2, they are one of the only filters that cannot easily be replicated in Photoshop or with software. 

So what exactly does a polarizer do?  Rather than get into the all the scientific details about how light works, let’s just say that polarizers help eliminate reflected light, and that has various beneficial effects on your photos.  Some of the beneficial effects include:
- Making blue skies a deeper shade of blue; this makes clouds really pop
- Enhancing colors, especially of foliage / leaves
- Removing reflections on water, allowing you to see through the water
- Removing reflections on glass, allowing you to see through glass
- Cutting out haze

If you’ve ever seen one of those landscapes with an incredibly rich, deep blue sky and puffy white clouds, you can almost bet a polarizer was used.  Polarizers are also used (especially by me!) on turquoise Caribbean-style water.  Looking at the water without a polarizer, you’ll see a white sheen of reflected light on the surface, and probably not much else.  It is doubtful you’d be able to see anything underwater.  Look through a polarizer and prepare to be amazed.  The sheen on the surface completely disappears and suddenly you can see completely through the surface down into the ocean.  It’s literally like putting X-Ray glasses on.  Suddenly fish, coral, and even the ocean floor becomes visible, when before without the polarizer you could see nothing.  This is precisely the effect that could never be replicated in Photoshop.  If you took a photo without a polarizer and now have a picture of a white sheen on the ocean, there’s nothing you can do after-the-fact in Photoshop to suddenly “see down through the water”.  Your “x-ray vision” is only available while you’re on-the-scene. 

 

The same principle applies to reflections in glass.  If you’re in NYC at Christmastime taking pictures of the displays in the store windows, with no polarizer on, you’re going to wind up with shots of glass reflecting thirty other onlookers looking at the display, and your photo may not even show what’s behind the window.  Put a polarizer on, and the reflections of the people disappear, and you see straight through the glass.

In a less intuitive way, this is also why foliage and other items look better and more colorful with a polarizer.  Leaves can be very reflective.  Without a polarizer, you’re photographing lots of white reflected light (think of the sheen on the ocean).  Put on a polarizer and you see through that reflected light, straight through to the leaf’s natural color.

So how do you use a polarizer?  Easy, attach it to your lens (described in more detail later) and look through the viewfinder to see its effect.  Polarizers are designed to be able to rotate while attached to the lens.  Rotating it varies the effect.  You can just experiment by rotating it to see how much effect it produces.  For blue skies, the amount it affects your photo (if at all) depends on where the sun is located.  Basically it works best if the sun is directly to your side (left or right) and somewhat lower in the sky.  This also happens to be when most landscapers take their pictures anyway.  Polarizers have less (or no) effect when the sun is directly overhead, or directly in front of or behind you.  For ocean shots, again it’s best on an angle.  I usually try to aim at a 45 degree angle or so to the water.  Shooting straight down on water with a polarizer will probably have little effect.  But again, how many times would you be shooting straight down on water?  For oceans, as with foliage, glass, or anything else, just experiment by moving around and rotating the filter until it produces the desired effect.  Once you start taking pictures with a polarizer, you’ll wind up always wanting to have one with you.  They can be indispensable in enhancing your photos.

I mentioned that there were two main categories of filters that you’ll mainly use.  The first is the polarizer.  The second is the Neutral Density filter.  Unlike the polarizer, which is really just one filter, Neutral Density filters (or “ND” for short) are a “category” of filters.  You’ll buy a few of them, each having a different (but similar purpose).  So what is an ND filter?  Real easy:  it’s basically just a pair of sunglasses for your lens.  Yep, an ND filter is just a piece of glass with a gray coating on it that blocks some of the light, just like sunglasses.  So why would you want to use one?  There are three main reasons:
- You want to use a long shutter speed but it’s too bright out
- You want to use a wide-aperture but it’s too bright out
- A portion of the scene is too bright but the rest is normal, so you want to darken just the really bright part

Let’s take these scenarios one-by-one.  The first reason you’d want to use an ND filter is because you want a long shutter speed but it’s too bright out.  We’ve all seen the photo of the waterfall with the beautifully blurred, silky water.  This is achieved by using a long shutter speed, sometimes several seconds long.  Even with a small aperture such as F22, if you try to take a two-second exposure during the day, it’s going to be overexposed and way too bright.  Solution?  ND filter.  With an ND filter over your lens, it lets in less light, and you can use a long shutter speed without overexposing the photo.  How much light does an ND filter block?  Each ND filter you can buy tells you how many “stops” of light it will block.  A one-stop ND filter will block one-stop of light…meaning you can double your shutter speed once.  For example, if using no filter at all, the longest shutter speed you can achieve is one second without overexposing, attaching a one-stop ND filter will allow you to use a shutter speed of two seconds without overexposing.  A two-stop ND filter allows you to double the shutter speed twice.  So in our previous example, you’d be able to use a shutter speed of four seconds.  (1 second doubled is 2 seconds (first stop) and 2 seconds doubled is 4 seconds (second stop)).  A three-stop ND filter allows you to double your shutter speed three times.  Using our previous example, you could shoot for eight seconds.  They generally come in those three levels.  I personally use the 3-stop version (I figure I can always open the aperture to let a little more light in, but if I buy one that’s not dark enough, there’s nothing you can do at that point).

The second scenario, wanting to use a wide aperture in bright conditions, is very similar to the one above.  If you’re trying to blur the background by using a wide-open aperture, and it’s bright outside, it may be too bright for even your fastest shutter speed.  For example, at F1.8 during the day, you may go all the way to 1/4000th of a second for a correct exposure.  If it’s still too bright out, there’s nothing you can do with the camera, if that’s the fastest shutter speed your camera allows.  Use an ND filter to cut down the light.  A 3-stop ND filter will bring your shutter speed from 1/4000th to 1/500th.  (4000 to 2000, to 1000, to 500 is three stops).

The third category is one of the most important, and is probably the category where ND filters are used most frequently.  If you’re photographing a scene that has one portion that is really bright but other areas of the scene are dark or normal, you can use an ND filter to even-up the lighting.  For those of you who have read my article on HDR, you may remember that cameras are not great at taking pictures of scenes that have both really bright and really dark areas.  Generally, you have to pick just one area to focus your attention on, and the other area will just come out too bright (or dark), and you just have to live with it.  ND filters fix this problem.  How?  It’s pretty simple.  You use a special ND filter that is a piece of glass where only half of it has the gray coating – the other half is clear.  This is called a Graduated ND filter, ND Grad, or just Grad.  You attach the grad to your lens in such a way that the dark part of the filter covers the bright part of the scene, and the clear part covers the normal part.  Thus, it darkens just the bright part.  A classic example is the sunset.  When the sun is setting, the sky is usually much brighter than the land.  If you’re taking a landscape picture at sunset and you set your camera so that the sky is properly exposed, the land will be too dark.  If you set your camera to expose the land properly, the sky will be too bright.  Using an ND Grad, you can place the dark part of the filter over just the sky, leaving the clear part over the land.  Now you can take the picture and both areas will be properly exposed.

Like regular ND filters, ND Grads also come in a few versions, generally ranging from one to three stops.  They also come in two styles – hard edge and soft edge.  The soft-edge filters have a smoother transition from the clear area to the dark area of the filter, so you can’t really see the dividing line.  The hard-edge filters have a more abrupt transition and are useful when you know you can put the transition line right on the horizon.  I personally use the soft-edge, three-stop version.  “Conversationally”, it’s a 3-stop soft-edge ND grad.

Some might say that software solutions such as HDR make graduated ND filters unnecessary.  While there are some occasions where this may be the case, there are other times when an ND filter is the only real option.  For instance, for any scene where there are moving objects, it is much more difficult to take an HDR image because the objects will have moved from frame to frame, and when you composite the multiple images there will be alignment problems that have to be solved.  With graduated ND filters, there is no issue, since you’re only taking a single shot.  The other primary advantage of using filters is time.  It takes a considerable amount of time to create HDR images, especially ones that look natural.  When using filters, you’re capturing the image with the all of the  highlight and shadow detail from the start.  That being said, for scenes with complex highlight / shadow ranges like nighttime cityscapes, HDR is still a great option.

Let’s talk about how to physically attach and use these filters.

There are two main types of filters – screw-in filters and “filter systems”.

Screw-in filters are the easiest to use.  They’re circular pieces of glass that fit the size of lens you own.  They have little threads on them (like a screw) and you just screw them onto the front of your lens when you want to use it.  They come in various sizes to match all sizes of lenses.  If you have multiple lenses of varying sizes, you have two options: you can either buy a separate screw-in filter for each lens you own, or you can buy one filter that matches the largest lens you own (by large, I mean the lens with the largest diameter at the front of the lens), and then buy little “adapter rings” that let you put that filter on smaller lenses.  These rings are called step-up / step-down rings depending on what you need.  The advantage of using the adapter rings is that you only have to buy one filter, which is much cheaper than buying multiple filters.  The only real disadvantage of using adapter rings is that with wide angle lenses, the rings make the filter thicker, and you may get vignetting (vignetting is a darkening around the edges of the picture, sometimes due to the lens itself, sometimes due to the edges of a filter being visible in the frame).  Polarizers can often be used as a screw-in filter.


The other type of filter is a filter that belongs to a “filter system”.  A filter system allows for much more flexibility.  It consists of three main parts, a filter holder, adapter rings, and the filter itself.  Let’s talk about each.  A filter used in a filter system is just a plain piece of glass that is not attached to anything.  Holding it in your hand, it just looks like you cut out a square piece of window and are holding it raw in your hand.  By itself, it’s not really useful since there is no way to attach it to your lens.  That’s where the filter holder comes in.  A filter holder is a rectangular piece of plastic with little fitted slots that you slide the filters into, and it holds them tight and in place.  Sometimes a filter holder has multiple slots so you can stack filters on top of each other for various effects.  Finally, are the adapter rings.  An adapter ring is just a small inexpensive metal screw-in ring that you buy in the size(s) of your lenses.  The filter holder is made to easily attach to all the different sizes of adapter rings.  So you just buy a few inexpensive adapter rings for the lenses you own, and now the filter holder will fit all your lenses.  Since all the filters you own fit in the filter holder, you can now attach any filter to all your lenses.  There are several advantages to the filter system.  First, purely from a cost perspective, this is an economical solution.  You buy one filter holder, one filter for any kind of filter you need, and a few inexpensive adapter rings, and you’re all set.  Any filter can attach to all your lenses and you don’t have to buy multiple versions of the same filter to fit all your lenses.  Because the filter holders can be made relatively thin and wide, and the glass filters can be wide, these filters can be used on wide-angle lenses without worrying about vignetting.  Most importantly, filter systems are necessary for using ND Grad filters.  You can’t really use a screw-in ND Grad (although they do make them).  The reason is because when you are using an ND grad, you need to physically position the transition-line (where it goes from light to dark) in the right spot for your picture.  So if you’re taking a picture of a sunset, and the top 2/3rds of the pictures is a gorgeous sky, and the bottom 1/3rd is the ocean, you need to position the transition line right where the sky meets the ocean.  With a screw-in filter, there is no way to move the dividing line once the filter is screwed on.  With a filter system, you can slide the filter up and down in its holder to position the transition line right over the horizon.  The filter holder also rotates so you can have the transition line on an angle.

The only real disadvantage to a filter system is that for the most part they work best on a tripod, so you can’t be very mobile when you have them attached.  This is because the filter holder is designed to rotate (so you can adjust polarization or the transition line of ND grads, etc), and if you handhold the camera it has a tendency to rotate on you.  More importantly, if you move abruptly, it’s possible that the filter may slide out of its holder and fall to the ground.  Screw in filters allow for more flexibility with handholding the camera.

There are countless other types of filters as well.  There are filters that can enhance certain colors, filters that create soft-focus effects, some that create small 8-point stars over bright light sources (I use this once in a while), the list goes on and on.  I don’t normally rely solely on the use of these other types of filters too much because many of these effects can be replicated using software.  I’d rather have the “original” unfiltered version so that I can apply the effects after-the-fact and decide if I like it or not, or how much of the effect to apply.  On the other hand, since I’m also a fan of capturing the scene as much as I can “in-camera” without having to use software, if I have the time I will take two shots, one with the filter attached and one without.

Even in today’s digital age, there is still a need for traditional photography equipment like filters.  With all the software in the world, it’s still not possible to replicate the effects of a polarizer or ND filter during post-processing.  The use of these types of filters will certainly help to take your photography to the next level.

I've also created an app for iPhone, Android, and iPod Touch which teaches you photography -- more info can be found here:

Photography Trainer for iPhone and Android

If you have any questions or comments, please let me know.

Best,
Paul

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