Purchasing Neutral Density Filters

ND filters (Neutral Density) remain one of the most essential accessories for Landscape Photography. When good quality filters are used well they will transform your landscape photographs. You might be able to achieve similar results by shooting and blending images with multiple exposures but this can be time consuming and complex. ND filters offer an ease and flexibility that is hard to match but they can be expensive. This article will explain what to look for when purchasing ND filters, helping you avoid wasting money.

Why Use ND Filters

I should start by saying something about why Neutral Density or ND filters are so valuable to photographers despite all the advances in digital. In short they allow you to control the light reaching your cameras sensor which allows you to control the exposure. Two broad categories exist, the full ND filter where the whole of the filter restricts light. These can be used to extend the cameras shutter speed, introducing blurring and motion into the image. The other type of filter is the Graduated filter (grads for short) where only part of the filter restricts light. These are used to help balance out the exposure across a scene where the contrast range between the lightest and darkest areas exceeds what the camera can handle. The name "Neutral Density" indicates that they are a neutral colour and should not have any visible impact on the colour of the final image.

The ND Filter

You would typically use an ND filter to lengthen shutter speeds for a particular aperture so that movement is blurred. An example might be when photographing a waterfall or the movement of waves. Although some camera manufacturers are now starting to build ND filters into their cameras, most of the time selecting the lowest ISO possible simply won’t give the sorts of duration that can be achieved with a ND filter. The strength of these filters tends to be measured in stops indicating how many stops they reduce the light by e.g. 3 stops, 8 stops and even 10 stops. Remember also that each stop of light you lose doubles the length of the shutter speed. By the time you have lost 10 stops of light you could be looking at shutter speeds of minutes, even in the middle of the day.

The ND Grad Filter

ND Grads are used to reduce the exposure of a specific area of the image e.g. the sky in a landscape to help balance exposure across the image. In a landscape for example, reducing the exposure of the sky allows the ground to appear brighter. Without using an ND Grad the ground would appear too dark or the sky too light. Even on a good DSLR, camera sensors currently have around 12 stops of latitude meaning the difference between the darkest point they can measure and the lightest point is only 12 stops. Even then you will find you need to keep the contrast range to around 5-6 stops to create a pleasing image. By reducing the difference in exposure between the brightest and darkest areas of the scene we improve the ability of the camera to create a good exposure. Again the strength of these filters is measured in stops but we will cover this shortly.

Which Filter Design - Round or Square

For both ND and ND Grad filters there are two options; round screw on filters that screw on to the front of the lens or Square filters that slot into a filter holder that attaches to the lens with an adapter. My own view is that for ND filters the screw in types tend to be better as they reduced light entering the lens from the top and bottom of the filter as can happen with the square filters. The drawback with the screw in filters is that if you need to use more than one the edge of the filter ring can cause a vignette around the edge of the image. You might therefore need more choice in terms of strength of filters than with a square system where you can slot two or three filters into the holder to give more of a light reduction. You might also find that some of the stronger filters for example the Lee big stopper 10 stop filter are not available as a screw on filter.

For NG Grads I wouldn’t recommend anything other than the square type filter. With screw in graduated filter it’s almost impossible to compose the image and line up the gradient part of the filter at the same time. You might get lucky now and then but generally you will find yourself making compromises all the time. Using a square filter format you can compose the scene and then move the filter up or down in the holder to line up the gradient. This is important as it hides the filter from being detected in the final image. It’s also possible to stack two or three filters in the holder to produce a stronger effect, although you need to be careful when doing this.

Round & Square filters

Round & Square filters

Accessories

For square filters, in addition to purchasing the filter you will need to buy a filter holder which attaches to the front of your lens and a filter adapter ring. The ring screws onto the thread on the front of the lens and then the adapter attaches to the ring. As different lenses tend to have different filter sizes you will need to buy the correct size adapter rings. This can at first seem complicated so let's take a better look.

  • Firstly, different manufacturers produce different filter ring systems although they are all mostly metal discs. In general they are not interchangeable with a few exceptions. So if you are using Lee filters buy the Lee filter holder and adapter rings. If you are using HiTech use the HiTech holder and ring combinations.
  • Different manufacturers produce filters of different sizes which we will discuss shortly. The size of filter determines which filter holder you will need. For example if you decide to use the Lee 100mm filters your will need a 100mm filter holder with appropriate lens adapter or your filters will not fit into the filter holder.
  • Many filter manufacturers now also have more than one size range. For example Lee produce the popular 100mm filter but also produce a series called Seven 5 which has filters that are 75mm wide. Filters from one series can't be used with holders from the other. Another example is Cokin which produce the A-Series filters which are 67mm wide and the P-Series which are 85mm wide. So remember, the width of the filter determines which filter holder it must be used with.
  • Now it is possible to use filters from one manufacturer in the holder from another (where they are all of the square slot in type) providing they are the correct width for the holder. For example, HiTech (also known by the name Formatt filters) produce a range of 67mm, 85mm and 100mm filters. These can be used with the correct HiTech filter holder but they can also be used with filter holders from other manufacturers where the filter holder is the correct size for the filter. So you can use a 100mm HiTech filter in a Lee 100mm filter holder and vice versa.
  • Back now to the subject of the adapter rings. As already mentioned you need to match the filter adapter ring to the filter holder in terms of size and manufacturer. So if you are using Lee 100mm filters you need a 100mm filter holder. You also need the filter rings for the 100mm filter holder and I recommend you pick the same manufacturer for the filter holder and rings to ensure they are compatible. If you use a HiTech filter holder then buy the filter rings to match it from HiTech also.
  • The other aspect of the filter ring size is the screw thread enabling you to attach it to the lens. If the diameter of your lens is 77mm then you will also need a 77mm adapter ring. This means you might buy a 77mm filter adapter for a 100mm filter holder. Don't get the two dimensions confused.
  • The final point about filter holders and adapter rings is that they can cause a vignette on some wide angle lenses. Some manufacturers produce wide angle versions of their filter rings or even filter holders. If you use wide angle lenses then do consider these. They are more expensive but they will save you the time and trouble of trying to correct vignette problems in post capture processing.

Filter Strengths

ND filters come in a variety of strengths indicating how much light the dark part of the filter will remove. These are measured in stops; one stop will double your shutter speed. Some filters are then rated with a multiplication indicator to show how strong they are. A 1 stop filter would be X2 (as it doubles the shutter speed, a 2 stop is X4, a 3 stop X8, a 4 stop X16 and so on. An alternative rating used by some is 0.3, 0.6, 0.9, 1.2 etc. These are also 1 stop, 2 stop etc.

If you can afford it, it’s better to buy your graduated filters in sets as this tends to be cheaper than purchasing them separately. A typical set will have a 0.3, 0.6 and 0.9 filter. If you can’t afford a full set buy the 0.6 first as this tends to be the most useful. The 0.9 then tends to get the most use after the 0.6 and the 0.3 least. You could of course pair a 0.6 and 0.3 in the filter holder to create a 0.9 filter so you might consider this to be a better purchase.

As well as different strengths you might also find the ND Grad filters from your chosen manufacturer are available as hard and soft grads. This refers to how short the gradient is between the dark and light area of the filter. Soft grads have a longer transition than hard grads and are more forgiving if you don’t light them up exactly. The benefit of hard grads is that they are easier to align because the transition is more obvious in the viewfinder.

Another factor is the size of your image sensor in your camera. A full frame sensor will be able to benefit from both hard and soft. If you are using a Micro 43 system you will likely find the transition of the soft grads is too large and that you really need hard grads.

Filter Sizes

Finally you need to consider the size of your filters as each manufacturer will offer a range of sizes which tend to measure the width of the filter. The most popular sizes are 85mm and 100mm wide. All three of the main filter manufacturers found in the UK (Cokin, Lee and Format Filters) produce ranges of filters in these sizes. In addition to these there are smaller filter sizes such as the Cokin A series and Lee RF75 (75mm) as well as larger sizes such as the XPro or SW150 (150mm).

Which size of filter is best for your camera will depend on the diameter of your lenses and also how wide your lenses are. If you shoot with ultra wide angle lenses you will most probably need larger filters to avoid problems with the filter holder creating a vignette. From my own experience:

  • Micro 43 systems are fine with 67mm, 75mm and 85mm filters. The 100mm filters are getting too large to use comfortably.
  • Crop sensor DSLRs tend to need 85mm or 100mm filters.
  • Full frame sensors usually need 100mm filters or larger depending on your lenses.

If in doubt check with the filter manufacturer.

Filter Manufacturers

Now you understand the options, which manufacturer to go with is an important consideration. In the UK we really have three choices at present for square filters: Cokin, Lee and Hitech/Format Filters. The general opinion is that Cokin and Hitech are lower quality than Lee and this is reflected in the lower price. A common issue is that many of the cheaper, supposed Neutral filters will produce a colour cast and therefore aren’t Neutral. Before you write off a manufacturer based on price let me share some of my experience.

I have purchased sets of Cokin filters in the past which were Neutral. I have however had filters from the same company and found they have a slight red colour cast to them which comes in handy when shooting in the early evening and at sunsets. The problem therefore is lack of consistency.

Lee filters have tended to give a neutral colour cast under most conditions however I have also shot images where the filters made the sky look a tobacco brown colour. The other people who were with me at the time also had exactly the same result.

Hitech/Format filters have also been a good performer for me however with some of my cameras I have found a slight purple tint was produced. I have also experienced this effect with the Lee filters but less frequently. I can only conclude that the Camera must also have some impact on this which probably supports the mixed opinions about the results people obtain.

What I would recommend is that if you can afford to, purchase the Lee filters although they seem to have shot up in price recently. If you can’t or don’t want to afford Lee consider the Hitech/Format brand. If cost really is the deciding factor for you pick Cokin.

For screw in ND filters I would select B W if you have the funds. Hoya also make good filters and are less costly.

Final tip is to ensure you have the filters in a soft case or wrap them in a clean lens cloth. You can pay a fortune for filters and then scratch them on your first outing if not careful.

Kase Wolverine Glass Filters

Since I wrote this guide, I have switched from using Lee filters to Kase Wolverine. These filter are very high quality and made from glass. Unlike otehr glass filters they are scratch and shock resistant. Drop one of these and it bounces rather than shatters. If you want the best quality filters for your photography you should consider Kase Wolverine. I was so impressed that I asked to become a distributor and now sell these in the Lenscraft Store.

Other Useful Links for Purchasing ND Filters

If after reading this article you decide to buy some filters please consider using the links below. I receive a small commission for purchases which I put towards the upkeep of this site. I am also happy to answer questions if you want to email me.

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