Are filters redundant?

March 14, 2017  •  Leave a Comment

Are filters redundant?

With the capabilities of modern digital cameras and processing software, is there still a place in the camera bag for physical filters that fit in front of the lens? Here are the three types of filters that I use. When I use them, when I avoid them and what the alternatives are in post processing. The first thing to say is that I always think twice before using any filter. Putting an extra piece of glass or plastic in the front of the lens increases the chances of capturing spots or dirt and also increases the risk of lens flare. I only use filters if I have a specific need of them to get the shot, or effect, that I want. The first type of filter is  the

Circular Polarising Filter or CPL

         

  These screw onto the front of the lens (or, as in the case of the image above, onto the front of a filter holder so that it can be used in conjunction with other filters). I'm not going to go into the technical detail of how these work, suffice it to say that they can boost contrast and saturation and also reduce glare and reflections. They are made up of two elements. Once screwed onto the lens the outer element can be rotated which will increase or decrease the amount of effect the polarising filter has. These filters are most effective when they are at 90 degrees to the sun. If the sun is directly to your left, directly to your right, or directly overhead, then the filter will have the most impact. If the sun is directly in front of or directly behind you then it will have little or no effect on the image. Perhaps not surprisingly I use a polarising filter when I am shooting at 90 degrees to the sun and mostly when I am shooting with water in the scene as it can help to reduce glare. I am very cautious about using one if I am shooting with a very wide angle lens, and especially if I have a lot of blue sky. The reason for this comes back to the 90 degree effectiveness. If I am shooting at 90 degrees to the sun but with a lens that has a 100 degree field of view, then the effectiveness of the filter will vary greatly across the image. If there is a lot of blue sky this can create an uneven effect that can result in unpleasant colour banding which can be almost impossible to correct. I never use one if I am shooting into the sun. As far as alternatives in post processing go. Saturation and contrast are easy to boost in tools like Lightroom or Photoshop. In fact it is easy to boost them too much and create images that look unrealistic. By the same token it is also possible to overdo the polarisation on the filter with the same unrealistic result. Glare and reflections are more difficult to deal with in post and this is when I think the polariser really shows its worth. As a side note on these filter they do block a certain amount of light, normally between one and two stops. For this reason they can be useful as a way to extend exposure times a bit. Conversely they can be a problem if shooting hand held in lower light conditions.  

Neutral Density Graduated Filters or ND Grads

These are filters, normally rectangular or square that are half dark and half clear, they are used to reduce the amount of light coming into the lens in one part of the image. The filters come in different versions that depend on how dark the dark part is and how sharp the gradient is between the dark part and the clear part. So, for example, a three stop hard grad would block three stops of light in the dark part and would have a fairly sharp transition from dark to light (note, some manufacturers would call this a 0.9 hard grad as each 0.3 equates to one stop)

A three stop soft grad would block three stops of light in the dark part and have a more gradual transition from dark to clear

                   

These filter are particularly useful when shooting a scene with a bright sky and a darker foreground. By sliding the filter in it's holder so that the transition between dark and clear is on the horizon it is possible to balance the light and get a good exposure across the entire scene in a single shot. Of course the challenge is that anything that sticks up above the horizon is also effected and could end up underexposed. I tend to use these filters when I am shooting seascapes and there is very little sticking up above the horizon line. There is something quite satisfying about being able to get a high contrast scene in a single shot. I avoid them when I have objects (tree, buildings, mountains etc) that extend above the horizon line as it can be a real pain to get the detail back in them later. The alternative is exposure blending (or HDR if you prefer that term) where several exposures are taken that are then merged in software to get a good balanced exposure across the entire scene. You can read my tip on creating HDR images in Lightroom HERE It's probably also worth noting that the dynamic range of modern cameras is much better than older models and so it's possible to capture even very high contrast scenes in a single exposure and recover detail in both shadows and highlights (assuming you're shooting in RAW of course). I still use the ND grads but not as much as I used to and, if I'm stuck for space in the bag I will take them out because I know I can always exposure merge.   The final filters on my list are

ND Filters

           

ND (or Neutral Density filters) have one purpose. They reduce the amount of light that gets to the lens so that the exposure time is extended. They come in a variety of strengths and styles. Most of them are square and fit into a holder in front of the lens although there are also some that are round and screw straight on to the lens thread. They range from one or two stops (blocking one or two stops of light) up to fifteen stops in extreme cases.

Personally I own two ND filters. A six stop (Lee Little Stopper) and a ten stop (Lee Big Stopper).

Just to put that into perspective.

A ten stop filter will increase the exposure time from 1/30 second to 30 seconds for the same aperture and ISO settings. This means that you can get some fairly long exposures even in quite bright lighting conditions.

I use these filters when I want to smooth out water movement or blur cloud movement to create an effect. It can also be useful if you have an otherwise static scene but there are people moving around in it. By extending the exposure you can reduce them to blurs. Extend it enough and, assuming they keep moving, they will disappear completely.

I don't bother using these kinds of filters unless there is movement.

ND filters are supposed to be colour neutral, thats what the neutral part in the name means. In general the cheaper versions tend to have a noticeable colour cast and the more expensive ones don't. In truth, even expensive heavy ND filters have a slight colour issue but this can always be corrected in post.

You can read my tip for correcting ND filter colours HERE

There are two alternatives to using these types of filters.

The first is to shoot when there is very little light anyway, the second is to use an averaging of multiple exposures to get the same effect.

You can read my tip for creating and extending long exposures in Photoshop HERE

This averaging technique works well to create moderately long exposures, say taking thirty 1/30 second exposures and creating a one second equivalent. You can use this technique with longer gaps between each individual exposure. say taking one 1/30 second exposure every thirty seconds and then averaging them. This would give a much longer exposure effect but it does tend not to look as smooth and silky as using a good filter in the field. For that reason I almost always have my ND filters with me so I don't miss out.

I will also just mention that ND filters and the resulting long exposures is one of those topics that people feel strongly about. There are those that shoot every scene that has some water or some cloud in with a long exposure. There are those that think the ND filter is a terrible idea and that the effect it produces (while once being innovative and creative) is now overdone and something of a cliche.

Personally I think there are occasions when it works really well and actually makes the image something special but I also think there are times when showing the texture and movement in water is a much better option. As with everything in this game it's all about what you choose to do with your art.

I hope you've enjoyed reading this, if you have, and if you have gained something from it, then I would be delighted if you would share it

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