Week 5: Depth of Field: the magic preview button and how to use it…

Learning objectives: 1.1; 1.2; 1.3; 1.4.

Each week we kick off class by communally critiquing the images we have all taken in the preceding seven days. In doing so, we invariably end up learning from each other (and shoring up the – in my case, shaky – knowledge we do have, at the same time). This week, Depth of Field came up and my classmate, Anna (who had taken some stunning photo’s of her daughter, see here) wanted to know how to blur the background of the shots more.

Depth of field is determined by three things:

Focal Length
Distance to Subject

By moving closer to your subject or, conversely, moving your subject further away from background info, you will achieve more blur in the back of the shot. The countless photo’s of my dog that follow on from this – all taken with a 50mm prime lens – go some way to illustrate this.

But if you want to be more precise about matters, depth of field, as a “rule of thumb that can’t be relied on” typically extends 1/3 before the point of focus and 2/3 beyond it, or, failing that, 50/50 either side of the point of focus. More or less. Kind of. But the lens you are using and how close you are to your subject can alter that considerably.

Gauging DOF can be hard: you can’t see any change in aperture when you look through the viewfinder and go to take a shot, this is because the camera keeps the lens wide to let as much light in as possible so that you can see what you are doing, right up until the point of shot. However, some cameras, like my Canon 600D have a “magic button” that helps to give a bit of a hint as to what the end effect will be. (My magic button’s found just below the lens release button. And, no, neither of these is an euphemism.) Push the “magic button” in and it closes the lens to the actual aperture selected, so you get a preview of the final focus (albeit the higher the selected f-stop, the darker the preview, as the lens lets in less light accordingly).

For a far more precise guide, go to dofmaster.com, where you’ll find handy, online depth of field calculators to play with. Whack in your camera model; lens focal length; selected f-stop and distance to subject and – bingo – all the info you need re’ total depth of field and where it starts and ends, is there in front of you. It’s a nifty little guide that can be especially valuable when you’re working with a new lens. For instance, if I wanted to use my 50mm prime to take some portrait shots from a distance of 2 metres, I can work out that f/2.8 will give me a DOF of 17cm – which is roughly the distance from the tip of someone’s nose to their ear – so would ensure that the subject’s face was fully in focus.

I figured I’d practice DOF myself this week, using the Queen of Richmond Park – Lola the magnificent – as my model. It’s not easy being both dog-handler and photographer but I think we worked well together (with the natural light available). That said, she’s so fricking beautiful you have to be a truly awful photographer to get bad shot of her.

As far as health and safety go, we were off the beaten path but I still paid attention to our surroundings and made sure that there were no other dogs or walkers nearby that we might pose a hazard to.

I can also say with hand on heart that no squirrel was injured in the making of this week’s portfolio, either.

Finally, for your delectation, some shots of things that are not my dog but have a bit of an autumnal vibe about them, also.

Forgetting the photography for a minute; Richmond Park is looking rather fabulous right now. Get up there, if you can. (Take only photos, leave only footprints, yaddah yaddah, else you want an earful off a mental woman with a large dog.)





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