Week 2: Depth of Field

 

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I can see clearly now…

Before this week’s lesson, I knew roughly what depth of field meant – that it’s the area/zone of an image that is in sharp focus – but that was about as far as my knowledge went. I hadn’t a clue how to manipulate it to my advantage when taking photo’s, or what actually has to happen within a camera for that manipulation to take place.

So here’s how I now see it:

What Influences Depth of Field?

  • Aperture number/size
  • Focal length
  • Distance between camera and subject

 

Low Aperture Setting = Shallow Depth of Field

For wide angle shots (18mm) the lowest aperture setting is F3.5
For telephoto shots (55mm) the lowest aperture setting is F5.6
Too technical? Small number = small depth of field.

What’s actually happening?

Wide lens + quick exposure = less time for less light/info to be captured.

 

High Aperture Setting = Wide Depth of Field

For wide angle shots (18mm) the highest aperture setting is F3.5
For telephoto shots (55mm) the high aperture setting is F22
Lost you again? Big number = big depth of field.
Typical uses: Close up portrait shots. Product shots/advertising.

What’s actually happening?

Small lens + longer exposure = more time for more light/info to be captured.
Typical uses: Landscape photography – hence need for tripod.

A mid-range Aperture – around F8 or so – will give a mid-range depth of field. So while there is slight loss of focus beyond the subject matter, you don’t feel it. This works well for photojournalism/storytelling, where you want to focus on the topic and give it a bit more zing, but not to the obvious exclusion of its immediate surroundings. You still need the image in context.

 

What you see is what you get…

For a true reflection of what you’re seeing, select an aperture setting of around F35.
(Can’t remember that? Think of it this way: by your mid-thirties, you should stop fooling around and be a bit more honest with yourself and others.)

By contrast, a shallow depth of field is used to extract the subject from its background – it muddies the scene – so that your attention is drawn more to the focal point/subject.

At least, I think I’ve got that right…

Homework was to set up a still-life of three items and then explore how varying the aperture settings; focal lengths and camera position changed the captured images. Which is why I took hundreds of photos of wine bottles and candles. (I also took some more shots of toy soldiers; the hound and her friends and some flowers, for good measure. If only to help refute suggestions that I am a pyromaniac and heavy-drinker.)

All photos on this page – bar the little red man – were taken in the subsequent week.

 


In an attempt to be artistic, I experimented shooting candles. I kept the camera more or less in exactly the same position but moved focal points (and sometimes the candles) and aperture settings. Only problem was I forgot my camera’s 0.25m macro limitations. Still, the overall effect was interesting, if a bit blurred. 

I wasn’t sure how changing the focal point would change the depth of field – did it extend from the camera or from the chosen subject was my query.

 

So, to find out, I took a battalion’s worth of shots, changing focal length, aperture and focal point, to see what happened. Not all the shots are here – and most that are have been consigned to a slideshow so that you don’t keel over with boredom. You can thank me for that, later.

 

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EXPOSURE COMPENSATION

We also covered exposure compensation: how by holding down the AV button and using the wheel to select options ranging from -3 to +3, you can quickly override the current camera setting and adjust the exposure. By doing so while in live view,  you can also see how the incremental adjustments will change the shot before you actually take it. A useful quick fix for a sunny day, say. Or, as is more likely, a miserable grey day with heavy rain forecast.

I completely overlooked the fact that I was supposed to practice this, too. So, until I do, here is a little red man kindly pointing out what I mean. And yes, my thumb is overexposed. And yes, I was cheating and using my iPhone.

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