Taking Control of the Variables

Thoughts about using a Variable ND Filter for landscape photography.

This article was originally written for a Formatt Hitech Ambassador Focus article. To see the fully designed article layout, visit the Formatt Hitech Blog.

 

I love shooting long exposures. I find there’s something freeing in not quite knowing how the shot will turn out. 

You’ve found a great vista with the clouds blowing towards you, or a perfect waterfall where the white foam will form streaks to draw the viewer in - but you still don’t know the exact shapes either of these will paint on the picture.

There’s something which engages my creativity, knowing I can only control the general composition, and that the overall success or failure will be governed by the random movement of the water, clouds, traffic, people…

When I started out, I was drawn to extremely long exposures, where water turns to milk and creates a soft, ethereal scene. As such, I jumped straight in and bought Firecrest 6- and 10-stop NDs. They’ve served me really well, and I do still enjoy the results I get with them.

But lately I’m finding that in some shots – especially flowing water - I’d like just a hint of texture to convey movement. Smoothing the water too much, while creating a peaceful effect, can soften the life out of the scene. Equally, too short an exposure will leave the image busy and harsh. 

An example with fixed NDs

This is an image taken a couple of years ago in Padley Gorge, one of the jewels of the Peak District. After a morning hunting for a scene just like this one, I had given up and was making my way back to the car. A final detour along the river and I found what I was looking for and set up for the shot.

The problem I faced was one of not having the right filters for the job. The tree was in a relatively shaded location and my least-strong filter was a Firecrest 6 Stop ND, which was totally blurring the water at 30 seconds. An unfiltered shot came in at 0.4sec and was far too crisp as it was a fairly wide view.

Too smooth with a filter, too crisp without

Could I have been more flexible with the camera settings and increased the shutter speed naturally? Of course that’s always an option, but the nature of the exposure triangle is that any change in one variable alters one aspect of the image or another.

I was already shooting at ISO 100, so reducing the sensitivity to lengthen the shot wasn’t an option. I could have dialled the aperture down, but on my crop sensor, getting past f/16 starts to soften the image. 

So, limited by the exposure triangle and the equipment I had in my bag, my approach was to take both images and blend them in photoshop, overlaying the sharper foreground to bring a certain amount of detail back into the smooth water. 

Don’t misunderstand me - the resulting image is one of my autumnal favourites, and I am more than happy with the reception it got - shortlisted in Outdoor Photographer of the Year 2018, and chosen as Digital Image of the Year at our local club. However, there’s still something which annoys me about the amount of work it took to create. I’m not averse to a bit of post-production, but it still feels like more work than you should need to do! 

A simple solution would be to buy a few more filters – starting with a 3- or 4-Stop, and perhaps a 1- or 2-Stop. But that’s a lot of glass to be carting around to allow for different lighting conditions on different days – and expensive too.

The Variable ND solution

When I heard that Formatt Hitech had brought out a Variable ND Filter, my interest was piqued. Although originally aimed at videographers, I could see how it might apply to the situation I was finding myself in.

That said, I did have my concerns. Variable NDs get a lot of bad press, and indeed my first foray into filters was with another brand’s product. It was bought for me as a gift, so I must be tactful here, but let’s just say it wasn’t great. 

It suffered from some downfalls, as cheaper products often do. I was lucky that it was largely free of colour-cast under moderate use, but did go a little purple when dialled up to the max. Crucially though, anything more than a minor adjustment resulted in uneven dark patches appearing on the image.

This is down to the way these filters operate. They are essentially two circular polarisers, one fixed in place, and the other allowed to rotate in front.

If you are not aware of how a polariser works, imagine it as a row of bars with gaps between. On the basis that light waves oscillate as they travel, when they reach the ‘bars’ of the polariser, only light which oscillates in line with the gaps can pass through. 

When you stack two polarisers to make a Variable ND Filter, you add a second set of bars. If one is rotated so that the two sets of bars are not aligned, even fewer light waves can find a way through, creating the ND effect. 

Cheap filter causing uneven darkening of the image

However, on cheaper Variable NDs, this can create uneven patches on the image where the effect is stronger in some areas than others. My direct experience of this issue left me initially wary of the Formatt Hitech offering.

However, the higher quality product they have produced means that this effect is pretty much non-existent. Part of the solution is that the maximum strength of the filter is limited to around 6 stops, while others claim to go as high as 10 Stops. Credit is due to Formatt Hitech for acknowledging the limitations of the technology, rather than marketing an unusable filter which can ‘technically’ achieve a stronger effect. 

Of course, the higher quality of polariser and glass also helps. As well as a reducing the ill-effects of poor polarisation, Formatt Hitech have worked hard to ensure minimal colour cast from the glass. Due to the limitations of polarising technology, there is an unavoidable but very slight warming tone to the filter. However,  shooting on AWB (or manually adjusting after mounting the filter) easily allows for the camera to compensate for that. They’re indicating this clearly in the name by not ascribing it the Firecrest moniker.

Reassured, I thought that it was worth considering as a way to provide some flexibility when shooting “short” long exposures - and I was impressed with the results..

Putting it to the test

I first tested the filter on a visit to Waterfall Swallet in the Derbyshire Dales, located in a deep sinkhole surrounded by trees. I had been before during the summer, with the leaves providing cover from the bright sunlight, but this second trip was in winter, and the bare trees gave no shade. The falls were in partial light meaning there was far too much contrast for a shot of the wider scene.

I searched for more intimate compositions and not wanting to re-shoot a close-up of the face of the falls, I decided to work with a clump of ferns hanging from a mossy rock - the vibrant greens contrasting with the greys of the waterfall behind. However, a shot at my usual f/11 contained too much detail throughout, looking flat and busy.

This called for a wider aperture, f/5 in this case, to provide separation by throwing the waterfall out of focus. As my ISO was already at 100, a faster shutter speed was needed to compensate. Using a filter was the only option in order to get back to the third of a second exposure I needed

The beauty of working with a Variable ND in this setting was that I could set the camera exactly as I needed and, referring to the live-view histogram, precisely limit the light levels for the correct exposure. Even if I had a Full ND from the weaker end of the range, and one which was ‘near enough’ what I needed, it would not have given the same level of control as  the Variable ND.

The other advantage is that the Formatt Hitech Multistop Variable ND has a rear ring which allows you to lock the orientation of back polariser, so it can perform the role of a normal CPL. I set it at an angle which cut out the glare from the wet rocks. The front polariser then rotates to apply the ND effect. This feature makes it somewhat equivalent to using the Firecrest holder with its built-in polariser. 

Flexibility to experiment

I was also able to make good use of the Variable ND on a shoot at the iconic Etive Mòr waterfall. Heavy snow and storms had significantly swollen the River Coupall and it was raging over the falls. That much water with a 6-stop ND would have been a white mist with no detail at all. 

Filterless, the shots were coming in at 1/60sec – far too short for a pleasing image – but the Variable ND allowed for just the right range of shutter speeds. The simplicity of being able to vary the exposure easily, without swapping filters, meant that I could quickly experiment with different versions of the same composition. 

 

The only problem this has left me is the struggle to decide which of these two I prefer! 

Again, the polarising aspect of the rear filter was important here as it accentuated the jade green of the water by limiting reflections on the surface.

Squaring the Exposure Triangle

With a decent variable ND at your disposal, you can exercise even more creative control over your images. You keep the wonderful uncertainty around the specific tracks and shapes the water will make - that creative partnership with the scene itself – but you gain greater control over exactly how you capture it. Choose your aperture, ISO and shutter speed - lock them in, and fine-tune the light levels to suit. 

In one sense, I think of it as turning the exposure triangle into a square. Of course, any ND filter will do that, but not with the degree of control a Variable ND can offer. This gives an immediate flexibility which is useful if the light changes slightly while you’re working on the image.

Some scenes and styles will undoubtedly need a strong 6-, 10- or even 16-Stop ND for the desired result but, especially when shooting flowing water, the Formatt Hitech Variable ND is now a go-to item in my photography toolkit.