Im a sucker for a long exposure shot. I love the way it conveys the passing of time into a single image, I love the contrast between pinsharp details and selected motion blur, and it can be used to document all kinds of scenes and environments, heres a favourite of mine - Waterfalls.
Before I knew anything about ND filters i just assumed it was something only pro’s with 70 years experience could do, it was a technique for the masters. How wrong I was, even I could do it. With the purchase of a piece of equipment no more expensive then a night down the pub it could open up a whole new avenue of images.
This is the sort of technique that gets covered throughout the range of Digital photography magazines in WH Smiths on a constantly rotating basis but if its something you’ve not given a try for yourself before, its definitely worth a go.
All you need is
- Trigger Release
- ND Filter Comparison App
The general jist of a long exposure shot is to allow your camera to keep its shutter open longer then usual in order to capture the movement of certain elements within your frame, such as cloud or water or even people on a busy street. We’e generally talking about shutter speeds that are longer then whats possible to achieve hand held so you’ll definitely need a tripod for this, and a fairly sturdy one at that. Because the length of time that the shutter is kept open recording the image it means that any slight movement of the camera or lens will be seen in the final image so absolute rock solid stillness is required. This is where the trigger release comes in aswel, instead of touching the camera yourself and risking shake we just press the trigger release and let the camera do its thing.
Apologies to anyone reading this who is familiar with an ND filter and what its used for, but Ill quickly run through the basics. With a regular image we are talking about shutter speeds probably in the region of 1/100th - 1/50th of a second, so the amount of light that reaches your camera sensor is minimal, but 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 bombarded with a constant stream of light which would completley over expose the image. So this is where the filter comes in, an ND filter is basically a darkened piece of glass which lets less light enter your camera and so 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, 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, theres definitely no shortage of choice. 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.
Now to get started with your image, go about your normal process in framing up your shot. Once your happy get the camera positioned on your tripod and make sure that its as secure as possible. 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 which when its supplied with fully charged batteries works great, usually.
Once these are all in place and the fully charged batteries are installed its now time to think about the image we want to capture. Im going to assume everyone is working in manual mode with achieving the correct exposure jut to make it easier - so you’ll have your ISO , shutter speed and aperture balanced correctly, and normally at this point you’d get straight into taking your shot, but this is where things differ alittle. 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. What this means is if your correct exposure is achieved at 1/50 of a second without the filter, with the filter you must change your shutter speed to 5 seconds to compensate for the lack of light. The app is working as a conversion chart for the correct shutter speeds using your chosen filter system, i use one called ND Filter Calculator which cost just a few quid off the Apple App store, but there are loads to choose from and some work easier then others for comparing.
Now adjust your shutter speed to the reccomnded speed from the Conversion char, all cameras work slightly different but my experience with Canons is that the shutter speeds can be dialled in anywhere up to 30seconds long, any longer than this and you will need to adjust your mode to ‘Bulb’ this basically means you can have your shutter open as long as you need without the camera ending the shot for you. Now When you look through your viewfinder your exposure meter will now 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 made the calculation.
So now we have the camera in place and we know how long the required exposure time is for your chosen setup, its about time to get your filter in place. Look through your viewfinder and make sure your image is still framed correctly and you have the right point of focus for the subject - this is important as we are about to turn the camera to manual focus (if you don’t already do so). Once the filter is applied to the end of the lens the camera will no longer be able to pick its point of focus as it won’t be able to see through the filtered glass, so by making sure the focus point is in the right place before we apply the glass we know everything is how we want it. Then once the filter is screwed on simply change the focus to manual, this means that when we come to take the image the camera won’t attempt to refocus with the filter in front it which will through everything out of focus. This is probably the most important part of creating a long exposure as we almost need to trick the camera into thinking the filter isn’t there.
Still following? Good.
So now we have everything in place, were ready to take the shot, one press of your trigger release to start, one to stop. On the viewfinder it should give you 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 were aiming for when it hits that magical mark press your trigger again. 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 light conditions change during setup slightly or your Filter might be slightly different to the one used in the chart. There is a slight room for tolerances.
Hopefully you should now have an image where your shot is pinsharp but a certain aspect of the photo has got some motion blur from the extended shutter speed. I hope this helps anyone looking to get this particular look, and would love to see anyones attempts at giving the technique a go.