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street photography - manual vs auto focus

Published March 4th, 2012

For my third post I want to relay my experiences from experimentation with street photography, specifically around focusing. Ok, some background:

I shoot alternately with a Fuji X100 and a Canon 5D Mark II (full frame), the latter with either a 28mm or 50mm fixed lens (the subject of later different blog article). The Fuji of course has a fixed lens equivalent to about 35mm.

So, to focusing on events that may happen really quickly what are the options and what works? First to the lens length - 28mm and 35mm have a greater depth of field than a 50mm lens at the same aperture, and hence are more forgiving, meaning that even if the focus point is not spot on, you still have a good chance of catching the action. I will come back to this...

Firstly, auto focus: I am not the most patient person, so mostly I don’t stand in one spot but keep moving, looking for something to happen. Many street photographers will hang around in one place (their 'stage') waiting for the 'actors' to play into position. I haven’t tried this much, but will do so in the future. Anyway, the point I am making is that not only are the 'subjects' moving, I am also moving, usually towards them. Auto focus, even on the AI modes I found simply would not keep up at these speeds, and most certainly not on the X100.

So, unless you are on a bright sunny day (assists rapid autofocus), and stationary, autofocus doesn’t seem to work too well. That said, I have read many posts of people that do use autofocus with success.. It just doesn’t work for me. I also found it would also lock on to something nearer, with no time for me to change focus points before the moment has passed. Thomas Leuthard as an example, does use autofocus, but he is braver (and more experienced) than me, and tends to shoot through the viewfinder - I tend to shoot from the hip.

On to manual focus. I found I had much more success by pre focusing to a fixed distance, and using hyper focal calculations to understand what my depth of field will be. For example, if I am planning to get some close ups of pedestrians with my wide 28mm, I have two options:

Option 1: Set manual focus to 2m at f/8. I know this will give me an in focus range of from about 1.2m to 5m. So, as long as I press the shutter when the subject is between these distances, they should be sharp (assuming my shutter speed is high enough - aim for at least 1/125, but preferably 1/500).

Option 2: Set manual focus to the hyper focal distance - if you don’t know how to do this, it’s quite easy - it’s a distance which you prefocus to give maximum depth of field. It varies between lens lengths and crop factors, but on my 28mm, if I pre focus to 3.29m, then everything from 1.65m to infinity will be in focus. The wider the lens, the greater hyper focal range. To look up your lens, try http://www.dofmaster.com. There are also iPhone apps to do this on the fly, but you soon get to be able to guess fairly well.

Incidentally, stopping down to f/16 will also increase the in focus range, but having practiced all this in a British winter, I needed all the light I could get, hence opened up to a minimum of f/8 at all times.

So, it all seems quite clear then... close down to f/8 or f/16, set shutter to 1/250 or 1/500 (and the appropriate ISO to allow this), and manually pre focus, allowing you to flick to auto focus for the occasional shot where you have time to compose yourself, then back to manual and refocus. Simple.

There is a downside: you won’t get any of those nice looking shots where the subject is sharp and everything else is out of focus. For that you will want a 50m lens or longer.

Oops, now we have gone to 50mm, suddenly our in focus range has dropped significantly. My pre focus at 3.29m (hyper focal for 28mm) now only gives a range from 2.51 to 4.78m - much tougher, but still not impossible, except it is now much harder to shoot from the hip. Try it. From 3m away, while moving, shoot from the hip and try to get a face in centre frame. Quite tough - I have missed loads of shots trying to do this. I could have sworn I was angling up and just got a picture of their groin.

So, for 50mm (which I like quite a lot), you need to slow down, be braver, use your viewfinder and autofocus to get a decent hit rate.

That’s all folks for this edition. Oh, except to say that burst mode is quite useful in hip / pre focus situations... start the frame burst as they are walking into your focus range, and keep it down until they pass. Just hope they don’t hear the machine gun noise and punch you.

See my best shots so far are at: 500px.com/markheathcote - please give your feedback good and bad to help me on the journey.

Also to be found at:

markheathcote.500px.com

www.flickr.com/markheathcote

www.markheathcote.com

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