Using Depth of Field in Conjuntion with Angle of View

Anne O’Connor 1st July, 2012

I have spoken of this before, but thought it worth mentioning again. For those who are not aware, when I talk about the ‘angle of view’ or another term, ‘camera plane’, I am referring to the angle that the camera is held in relation to the subject. This is what really affects the aperture settings or Depth of Field (DOF) and focussing points in taking images. I hope what I have put together here makes sense, but if it doesn’t, get in touch with me sometime and I will try to show you using a camera. 

If you think about your lens and think about using it, you will notice it is often angled when taking an image. It is worth getting your camera out to check this out because it is very difficult to explain what I mean. So basically when you take a photo, you often do not become aware of what is happening at the lens end of the camera. Generally we angle our cameras towards a subject, either upwards or down. This creates a varied distance from the top of the lens, the middle of the lens and the bottom of the lens to the subject you are focusing on. This is why we need DOF as a way of getting everything sharp if we want sharp. If we take images with no angles, meaning the lens will have an equal distance to the subject from top to bottom, the DOF is more accurate, except when the subject has different bits that are at different distances from the end of the lens. Again it means that the distance to subject is variable. Now I am going to go away from this for a time and talk about focus points. 

Focus points link into all of this as well, in particular the angle of view. Yes it is all very technical but important. The camera automatically focuses on a spot, often based on the automatic settings you make as to focusing, quite often in the middle of the lens. It can be one spot focusing or more. So when you consider your subject, you need to make a decision as to what you want sharp and focus on that, holding this when you re-frame your subject by keeping the shutter held down. The decision over sharpness is factored based on your considering the various angles that present themselves in relation to the ‘angle of view’ (the lens) and the subject which could have different bits that are at varied angles or distance to the lens. This will apply with whatever image you are taking. Automatic/P settings make their decisions based on you holding the camera at an even distance from the lens to the subject and assume the subject has an even distance all over from the subject back to the lens. So it is important to consider your angles when about to push the shutter. 

Many of you would have had images that have the foreground blurry or the background blurry with just the middle bit sharp. This is the result of the varied angles that present to the camera lens without factoring them in, plus it can be the focus point you have used or the camera has used automatically when clicking the shutter. You may also have had people shots where parts of the body are not sharp, such as face or eyes. This can be the result from the same thing. Especially if you have the body angled towards the lens with some parts of the body further away and some parts closer. 

To fix it you need to start playing around with the DOF. F8/F11 can be a reasonable DOF to deal with a lot of things, but again if the angles are really big based on the angle you have the lens at, then you may need to go to F22. A rule for focusing with people is about focusing on the eyes to get the face sharp. Landscapes, focusing 1/3 of the way into the image on F22 and let the DOF do the work for you. The DOF allows a small percentage of sharpness 1/3 in front of the focus point and around 2/3 beyond it. However, the distance it carries beyond and in front of the focus point varies with each aperture setting. I would suggest you play around with some images, angling your camera, keeping it straight and using different focus points and DOF settings. 

However, the most important thing to remember is to know what you are doing with the angle of view that your camera has at the lens point and adjust settings accordingly. Alternately if you want to keep the lens wide open with light, using a small DOF number, you do need to keep the camera plane or angle straight. Bend your knees, kneel down or stand on something if you have to during this process. Also make sure you focus on the point you want to be sharp and hold that focus point, by either keeping the camera shutter down as you move the lens back to where you want it to be to frame appropriately. Otherwise if you happen to have a focus lock on the camera, this will do the same thing. I have often pre-focussed, and then turned off the auto focus, but you do have to remember to turn it on again to re-focus if you change your shooting angle. Once again, have fun, experiment and if you want help, just ask.