Lens Flare - why I do not like it, and how I try to keep it out of my photos.
The two pictures above illustrate a not-unusual situation when photographing towards a light source (in this case the sun, but similar situations arise when photographing under street lights, or in interiors lit by artificial light sources). The lefthand picture shows what the camera sees, while the righthand picture shows what the photographer sees and, probably, what the photographer wishes the photograph to look like. The name given to the phenomenon seen in the lefthand picture is 'Flare', or more completely, 'Lens Flare'. Flare could be termed an optical illusion, because it is an artefact of the photographic process, existing only within the lens and camera and caused by stray light from the light source bouncing around within the lens and camera. It manifests itself, as well-revealed in the lefthand shot, as an overall haziness or 'flatness' in the image, often accompanied by hazy patches, and blobs and coloured shapes, which follow a line diametrically across the image from the position of the light source. The reason this constitutes a problem for me is because the stray light is not image-forming light - it is not part of the image that I have physically seen with my eyes, and certainly not part of the image that I have visualised in my mind's eye. Therefore, anything that I can do to exclude flare and achieve the image shown on the right will be a positive step towards creating the 'picture in my head'.
It is a fact that if flare is present in the camera, then it is visible in the viewfinder. In spite of this, many photographers fail to notice the presence of flare until some time after the event. Only when the photo is on the screen or the print is being held up for scrutiny does the photographer remark: "I don't remember even seeing that at the time". As Sherlock Holmes was fond of reminding Watson, most of us "see everything, but observe nothing". So step one in the avoidance of flare is: to be on the alert for the occasions when it might be an issue. These occasions are always when the camera is pointed towards a light source. It is not necessary to include the light source within the picture's frame for flare to be possible, but if the light source is intended to be visible in the picture (such as in a sunset photo, for example), then flare of some form is inevitable. However, various factors can influence just how prominent the flare is in the final picture, and sometimes it can remain, to all intents and purposes, invisible. The two main factors (in my experience) affecting how bad the flare looks are 1). the atmospheric conditions; and 2). the specific characteristics of the lens in use. Only time and experience can demonstrate to you how each of those things will affect your own photographs.
So, having started to be on the look-out for situations where flare may be encountered, how can we start to make ourselves able to perceive the flare in the viewfinder? First, we need to know that it is there - "the last time I took a photo like this, the print was spoiled by flare, and I didn't even notice it. So this time, let me see if I can see it before I fire the shutter". Looking through the viewfinder may not be sufficient to reveal the flare; but by holding an arm out in front of the camera, and casting a shadow across the front of the lens (shading the lens) may reveal a change in the contrast of the scene in the viwfinder. Moving your hand back and forth, removing and then re-casting the shadow, can show the contrast of the scene snapping back and forth, allowing you to see exactly what the flare looks like through the viewfinder. If you have a depth-of-field preview lever, and you set a small aperture, operating then releasing the lever can, in a similar way, demonstrate the presence of flare - flare tends to be more pronounced at small apertures, and even though the viewfinder image darkens when using the preview lever, it should soon become apparent if there is any flare present.
So, here we are in Holehird Garden above Windermere (photo above). We like the scene looking towards Langdale and the setting sun (by definition, this will give rise to the possibility of flare because we are pointing the camera at the setting sun). The picture above represents what we want the final picture to look like. We set the camera up on the tripod and compose the scene. (Using a tripod has several advantages: it allows multiple identically-composed images to be taken, since the camera doesn't move between shots; and it allows the use of a cable-release, which makes the process of shading the lens while looking through the viewfinder more straightforward).
With our new-found level of awareness of flare, we spot the fact that flare is present when we look through the viewfinder (as we can see in the picture above). By shading the lens with our hand, then removing it, or by using the depth-of-field preview lever, we confirm the presence of flare, and because we are using the camera on a tripod, we can keep our eye to the viewfinder as we shade with our hand to observe the moment at which the flare disappears, and then fire the shutter.
It is worth knowing that most SLR camera viewfinders only show approximately 90% of the view seen by the camera. This leads to the fairly frequent appearance of un-noticed and unwanted objects at the edges of our carefully composed photos (such as the shading hand along the top edge of the picture above). It is therefore a good idea to take more than one shot when shading the lens to avoid flare (there really is no excuse in the current digital age - no film will be wasted if you expose several dozen images onto your memory card). This will increase the probability that you will have one shot that has excluded the flare, and also has the bonus of not featuring your shading hand creeping into the top of the frame.
I also direct your attention to the home page of this blog, where I write about a relatively new phenomenon called 'diffraction flare', peculiar to digital cameras. It's in the post about Rob Freeman's House.