This is a step by step guide to the technique of long exposure photography accompanied by a bit of background information as to why we need to do what we’re doing.
– Trigger Release
– ND Filter
– ND Filter Comparison App
Put simply the point of a long exposure photo is to allow for one element within your frame to display movement and everything else to remain still, the moving part of your image could be cloud or water or even people on a busy street.
It’s usually the contrast between the blurry movement of your chosen element and the sharp detail of everything else that makes these types of image stand out so its important to get both looking as good as possible.
So lets take a waterfall as an example, the flowing water is probably going to be your moving element and the rocks will be the sharp detail.
Thinking about how the camera works we can understand how the display of movement is captured. With a super quick shutterspeed, say 1/1000th of a second we are capturing the water in such a tiny fragment of time that we are seeing it almost frozen in that moment – it looks sharp and detailed and you can probably see every droplet. In 1/1000th of a second the water doesnt have a chance to move hardly at all, if for example the shutterspeed was increased to 1 second the water has had chance to move alot more in that amount of time – especially if its fast moving water. So during that 1 second your camera is capturing the waters journey from point A (the moment you open the shutter) to point B (the moment you close the shutter).
If the other elements within your frame havn’t moved, for example the rocks, then there will be no change, they should look sharp as they would in a regular image. The water however has been captured in flow over the duration of 1 second and so it will look blurry as each step on its journey has been recored in your image. The longer we leave the shutter open the more movement is going to be captured and so the type of blurry effect achieved can look vastly different. It also depends on the speed of your moving object.
It may already seem obvious but as this is a step by step guide lets cover it anyway.
To capture these types of images one function of your camera is key – the shutterspeed. We need to control it and keep it open for the amount of time needed, obviosuly we can do this by selecting our shutterspeed as we normally would within camera, but with this method we change things up alittle. We are going to use bulb mode as opposed to your regular ‘aperture priority’ or ‘manual mode’.
The difference with bulb mode is that we can control when the shutter opens and closes. Usually we press the button and the camera takes care of business, it opens and closes the shutter for the amount of time we told it to, but in bulb we are taking control. One press for open, and another to close. The limit of having the shutter open is 30 seconds in our standard modes, but in bulb we can hold the shutter open for as long as we want too.
So were opening up the shutter for long periods of time to capture the movement of the water – doesnt that mean huge amounts of light are coming through to the sensor and over exposing the image? Yep, thats a basic principle of using an SLR, longer shutterspeeds means more light coming through. So how do we compensate for this excess of light – ND filters.
With a regular image we are talking about shutter speeds probably in the region of 1/500th – 1/50th of a second, so the amount of light that reaches your camera sensor is minimal, when we start to open the shutter for extended periods of time from seconds through to minutes it means that the sensor of the camera is flooded with a constant stream of light which would completley over expose our image. So this is where the filter comes in, an ND filter is a darkened piece of glass which lets less light enter your camera and allows your shutter to stay open longer without blowing out your shot.
They generally come in a range of strengths from ND2 upwards, the bigger the number the darker the glass and so the less light is penetrating your camera. A quick search through the digital shelves of amazon will through up a million different options, with graded filters, square formats or circular. I don’t want to list every type of filter available or its specific purpose as this is something to be explored once you get a grip on the technique and how it can effect your shot taking but just be aware that there are many different types all doing different jobs.
e who uses automatic focussing there is one thing to be aware of with ND filters. An ND4 filter is relatively transparent, it provides a reduction in the amount of light hitting your camera but it is still see through, so your camera can see through it and focus on your scene. But if we are using an ND10 filter the glass is almost completely darkened, hold it up to your eye and you won’t be able to see through it, and this is the case for the camera too – it cant see through the glass to pick out an object to focus on. There is a way around this though, setup your shot as normal choosing your focus point then just before your going to put your filter on switch to manual focus. This will mean the camera maintains your focus point and when it looks through the ND10 filter it wont get stuck in a loop of trying to find focus as it now effectively in darkness.
Step 1 – frame up your shot
Go about your normal process in framing up your shot. Although we’re using this technique to bring something a bit different to your image the same rules apply regarding composition so don’t forget this part of your process. A fancy technique wont make a badly composed image work any better.
Step 2 – Setup your tripod
Once your happy get the camera positioned on your tripod and make sure that its as secure as possible, your relying on the clarity and detail of the still part of your image to contrast with the motion blur so make sure its solid.
Step 3 – Connect your trigger release
Nows your chance to hook up your trigger release, theres many different ways of doing this so whatever works best for you – I use a cheap wireless version. The point of the trigger release is to remove your need to touch the camera and reduce any shake that might be caused by it.
Step 4 – Exposure
Im going to assume everyone is working in manual mode with achieving the correct exposure – so you’ll have your ISO , shutter speed and aperture dialled in and balanced correctly, make a note of your shutterspeed as youll need this for the next step.
Step 5 – Exposure conversion
At this point you’d get straight into taking your shot, but this is where things differ a little. Take note of your shutter speed, and load up your ND filter comparison app on your phone, in here it will ideally have a list of shutter speeds alongside a choice of Filter densities (probably from ND2 – ND10), compare your shutter speed in the app and look under your chosen filter. So for example 1/50 using an ND8 filter gives us 5 seconds of exposure time, 1/4 using a 10stop gives us 4minutes exposure time. This means that if your original correct exposure is achieved at 1/50 of a second without the filter, then with the filter you must change your shutter speed to 5 seconds to compensate.
The app is working as a conversion chart for the correct shutter speeds using your chosen filter density, I use one called ND Filter Calculator which costs just a couple of quid off the App store, but there are loads to choose from and some work easier then others for comparing.
Step 6 – Adjust exposure
Adjust your shutter speed to the recommended speed from the Conversion chart, as we mentioned earlier if its over 30 seconds you’ll have to change to Bulb Mode. Now When you look through your viewfinder your exposure meter should read that your proposed settings will over exposure your image as it does not know you will be using a filter, but this is fine as we have compensated by making the calculation.
Step 7 – Change to manual focus
As mentioned earlier now is the time to change your camera to manual focus to avoid the camera trying to re-focus through the filter.
Step 8 – Apply filter
So now we have the camera in place, your image is composed and you’ve pre-empted the camera’s attempt to refocus through the filter, its time to get your filter on.
Step 9 – Take a photo
We’re ready to take the shot. One press of your trigger release to start, one to stop. On the viewfinder it should display a timer once you press the shutter for the first time, so this will tell you how long you’ve been taking the photo for, and referring back to the exposure time from the ND calculator we know what we’re aiming for.
Even with the conversion app you might need to take a few shots – reviewing your final image and histogram after the photo has been taken as conditions change during setup, or your filter might be a different brand to the one used in the chart. There is a slight room for tolerances.
Step 10 – Enjoy your photo
Hopefully you’ve now got a belting shot but if it does’nt work out on the first try – persevere, these kinds of setups take time to get your head around but with a few trials and maybe a few errors you’ll find the best way it can work for you.