I have been asked by a few people recently why I use filters and what the advantages of them are so I thought I’d write a short article with a few examples to show the benefit of using graduated filters to improve the images you shoot in camera. Before we talk about the filters though we need to understand how fantastic our brains are.
When we look at a scene our vision captures an extraordinary amount of detail from the very darkest shadows to the lightest highlights. In fact we can see around 24 stops of light (a stop is either the halfing or doubling of the amount of light coming onto the sensor). In contrast our expensive cameras have a limitation of somewhere between 11 and 13 stops which means that we will see a scene better than a camera can depict it, especially when there are large differences between light and shade within the scene that is being photographed.
I use the Lee Filter system, primarily because the quality of the glass they use is so good that the image isn’t impacted by the extra piece of glass that has been put in front of the lens but the principles I am going to discuss here are the same for any manufacturer. There are a number of different types of filters that you can buy, however, today I am going to concentrate on soft graduated filters. As you can see from the image, a soft graduated filter has a dark area at the top of the glass and then it gradually fades to clear at the mid-point of the filter. You’ll see shortly how we can use this to help take a well exposed image in camera.
I have used a fairly typical landscape scene to demonstrate the use of the filters. When I was looking over Edinburgh I could see lots of detail in the clouds which is the brightest part of the image and I could also see the grass being lit up by the setting sun in the foreground and the detail of the Dugald Stewart Monument that sits on Calton Hill. However, if I took the photograph in the camera without any filters on I would either set the exposure for the sky in which case the foreground became very dark or I could instead expose for the foreground and the sky would be blown out and lose all that interesting detail.
By looking at the histogram of this first image we can see that the highlights (in this case the sky) are right on the edge, however, the shadows on the left hand side are losing some of the detail.
Alternatively, I took a second shot which was exposing for the shadow detail (in this case the foreground) and you can see that this one brings out the grass and the monument, however, the sky has now become blown out and all that gorgeous detail in the clouds has been lost.
The histogram really shows how much detail we have lost on the right hand side by trying to get all the detail we want in the foreground
In order to get the picture that we are seeing with our eyes we need to balance the exposure we had for the sky in the first image with the exposure we had in the foreground for the second image and this is where filters help. You will see that the difference in the length of the exposure is equivalent to 2 and 1/3rd stops of light. As a rule of thumb I always add a filter with an extra stop that the difference between the two exposures, so in this case I have added a 3 stop graduated filter to create the final image which I am sure you will agree is a much better balanced image giving us the best of both worlds, detail in the sky and the foreground.
The histogram for this final image shows us that we have a well exposed image with the highlights and shadows both contained within the boundaries.
There are other ways of achieving a similar result where you can bracket images in the camera and then using software to merge the images after. However, I enjoy my photography when I am in the field, experiencing the location and would rather not spend time in my office editing to get the image that I can see before my eyes. I would much rather use a few seconds at the location to add a filter and save time in editing later.
Hopefully you can see the benefit of using graduated filters from this short demonstration. I like to spend time on my workshops exploring how we can use different filters to get dramatic effects and this is a taster of the kind of things we go over.