Photo tips on Saturday: using filters to vary shutter speed
Last Saturday I introduced creative effects that can be achieved by varying your shutter speed when making landscapes/seascapes (see here). In today’s photo tips on Saturday I will discuss one method that allows you to vary your shutter speed without under or over-exposing your image: by using filters.
As a recap, last week I discussed three types of shutter speeds, those that:
- freeze motion
- emphasise motion
- smooth motion.
Freezing motion used the fastest shutter speeds and smoothing motion used the slowest. The focus today will be on shutter speeds that emphasise and smooth motion. To achieve these slower shutter speeds, filters that reduce the amount of light hitting the camera sensor are useful. Without changing your ISO of f stop use of these filters reduce the light therefore resulting in the need for a longer shutter speed to achieve a well exposed image. In other words, it is a similar effect to changing from a lower f stop (e.g. 5.6) to a higher f stop (e.g. 16) but without changing the depth of field associated with an alteration of the f stop.
I find two types of filter are useful for slowing the shutter speed:
- polarising filter
- neutral density filter.
In relation to neutral density filters, to be clear, I am not talking about graduated neutral density filters (which have other useful benefits). Graduated neutral density filters are useful to ‘even out’ the light exposure when you have bright and dark areas in the one image area. In contrast, the neutral density filter reduces the amount of light hitting the camera sensor uniformly.
Slowing the shutter speed is not the prime purpose of polarising filters. Essentially, polarising filters do the same job as your sunglasses so one of the significant benefits is to darken the sky (noting this is maximised when shooting at ninety degrees to the sun. There are significant other benefits to polarising filters and lots of resources on the internet to their use so I suggest you do a search if you want to learn about their benefits. If you feel unfamiliar with polarising filters such a search would be very worthwhile – these filters are incredible useful and I would consider their use to be essential in landscape photography.
Most p0larising filters will reduce the light hitting the camera sensor by 1-2 stops, hence their side effect of blurring motion. This degree of effect is useful for emphasising motion such as in the photo below.
Neutral density filters
Neutral density filters are available in a wide range of density. I find it useful to think about the number of (f) stops the specific filter relates to. Some are available as a screw on whereas others slide into a holder which screws on to the lens. If you do a search you will see a range of makes available. The filter with the greatest density I am aware of is the so called Big Stopper (10 stops). For what it’s worth I own two neutral density filters that I use to prolong the shutter speed a 3 stop filter that slides into a holder and a 9 stop screw on filter).
Below is a photo taken with the 9 stop filter on. This is the filter that I find most useful for smoothing motion.
One of the key issues to avoid with stacking filters is vignetting. In general, I find it useful to stack a graduated neutral density filter and a neutral density filter but that is usually as far as I go. In my hands, the combination of polarising filter with neutral density filter produces vignetting
Other points when using the high density neutral density filters
My 9 stop neutral density filter is very dark. Focussing first, without the filter on is an important step. A number of people also recommend calculating the shutter speed you require based on the suggested shutter speed before you place the filter on. There are apps available for your smart phone to assist with this. However, I haven’t found this step necessary. I try to keep the shutter speed no longer than 30 seconds (which is my maximum shutter speed on my camera before needing to go to the bulb setting). If I found myself in a situation where I wanted a longer shutter speed, I would then make use of one of the phone apps to assist with the calculations.
As an example of the impact on shutter speed, if I had a suggested shutter speed of 1/30 before screwing on my 9 stop filter, then the equivalent shutter speed with it on would be 17 seconds -this was close to the situation in the above photo (taken at f 16 about an our before sunset).
Help with using the new techniques
If you have any burning questions from this post please feel free to let me know. I will be building on this post in upcoming weeks. At this point you may wonder how to go about varying the shutter speed – I will discuss some options including ISO, f stop and filters in coming posts – but feel free to experiment now.
I will repeat the advice I provided last week to assist putting new learnings into action. One option you may wish to pursue is to:
- create your own post with any photos you wish to show
- create a link to my post
- include a link from your post in my comments.
Next week I will look at f stops, lens sweet spot and shutter speed
March 21: Varying ISO to obtain your desired shutter speed
March 28: Pulling together ISO, f stop and filters to obtain desired shutter speed.