Depth of field is an area many photographers get confused about.
By changing the aperture in the lens, you can make the final picture have more of the picture in focus from near to far, or you can limit the picture’s focus on one place. For portraits a shallow depth of field (in many peoples opinion) gives far better results than a deep DoF. For landscapes the opposite is preferred, obviously this is personal preference and should be decided whilst taking the picture.
At ƒ1.8, the focus point will be much more defined with things in front of and behind the subject becoming softer looking the further from the subject they are. This is a very nice way to bring attention to the subject, i.e. portraits.
At ƒ22, the focus will seem to be sharp from very close to the camera to pretty much infinity. This is great for giving a sense of the place you shot the image, or for including many people in the image and keeping everyone clearly in focus or landscapes where you want as much detail across the image.
There are limits to how that will appear in the final image.
Exercise: Find a subject/object that is still or will be in one place for a couple of minutes. Stand about 2 feet from the subject and focus on it. Set your ƒstop to 1.8 (or a close as possible to that based on the light) and set the shutter speed to get a proper exposure according to your meter. You can set the camera to Exposure Priority (AV mode) and let the camera set the shutter speed automatically. You should be using 50 mm lens or a zoom lens set to about 50 mm.
Now set your ƒstop to 16 and change the shutter as needed.
Step back to about 10 feet from your subject and re do the above settings – first at ƒ1.8 then at ƒ16.
To really push this exercise, try all the above steps with different lenses or at different lengths if you have a zoom lens – i.e.. try it at 35 mm and at 200mm, or whatever your zoom lens range is. You will find the images can look totally different, sometimes a lot punchier.
The way DOF was explained to me when I was younger (and using negative, not digital) was this: if you have the lens aperture shut right down you will have a greater field of focus because the shutter is open longer meaning the subjects have more time to burn/focus on to the negative, wide open you will have a narrow field of focus because you are not giving the subjects enough time to burn on, it sort of made sense having it explained like that, think of when you are looking at stuff in bright light, you see more because thing have more time/light to burn the image to your eyes/brain, in low light you can’t pick out as much because it doesn’t have the same light and time, think about it, to focus more you need to squint, squinting is much the same as shutting the aperture you look longer at the subject therefore burning the image for longer to your eye/brain!
Why don’t you have a go for yourself? You now have the advantage of digital so you can take 100’s of pictures and not worry about the price of processing like I did when learning. Pick a bright day (this will become apparent why when you shut the lens down) and pick a subject in the garden, one flower maybe, with plenty of stuff in front and behind it so that you can experiment. Don’t try to compare the images on the screen of the camera, its too small to really see a huge difference.
Well, without sitting down with each and every one of you or getting too technical (If I did that you’d stop reading) thats it for this lesson, for now. If you have any questions then please leave the in the comments below, hit me up at email@example.com or my BBM channel BBMC C0045B753
If there is a subject you would like me to cover next time then also let me know at the above places, if not then next lesson I’m thinking of the other side of the coin… TV (Time Value) or Shutter Priority, also a semi automatic mode where you decide the speed of the shutter for different effects!
Till next time, keep snapping!