Getting off Auto - Depth of Field

I needed to take a few images to help explain Depth of Field to someone, so I thought it would be useful to utilise those pictures for another in the intermittent Getting off Auto series.

Usual disclaimer about me using Canon terms as that is what I use.  Earlier GoA threads (on Settings, Exposure+, Post-Production, Choices, Extras, Impossible Pictures & Ethics) as well as other interesting stuff about photography can be found by looking at the GoA Index.

Being able to control the depth of field in a picture is a useful thing as a photographer.  It is all about deciding exactly how much of the image is acceptably sharp and how much is blurred.  What is deemed “Acceptable” relates to some interesting physics relating to a setup’s “Circle of Confusion” – but don’t worry, having mentioned the term, I’m going to ignore it!

If everything is in focus (or nearly), you can easily lose your subject against a boring background, whereas a shallow depth of field will help to isolate the subject nicely from all that distraction.  These two images of a handy garden visitor show what I mean – the first is a bit lost against the brick wall, the second stands out much better with the blurred background.  I haven’t done anything different to the processing on these, the only difference was that one was taken at f/4, one at f/18.

I took the pictures at a distance of 80cm (the wall's around 3m behind).  With a 105mm lens on a full frame camera, that gives me a DoF of 1.2cm at f/4.  That increases to 5.4cm at f/18 and that does help get all of the bird in proper focus (the left hand side of the bird is less focussed on the f/4 shot), but I prefer the f/4 image for the way the bird is isolated.  The pictures also highlight how the transition between focussed & blurred changes – at wider apertures like f/4, the transition to out-of-focus is quite fast, whereas closed down, it’s a much more gradual affair – like this. 

How well you can use a blurred background to isolate your subject depends not only on the aperture used, but the distance to the subject and the background and even the sensor size (well, the field of view really, but sensor size is easier to get your head around!).  Big sensors make it easier to get a shallow DoF.

I keep talking about the Depth of Field I’m getting – how do I know?  I’m not completely all-knowing, I’m using a Depth of Field calculator.  I’m using an App on a phone, but you can get online ones via a web browser.  Plug in your sensor size, lens focal length, distance to subject and it will tell you what your DoF is.

The Hyperfocal distance is the distance from the camera that will be acceptably sharp should you focus at infinity.  Or, to look at it another way, if you focus at the Hyperfocal point, the image from Hyperfocal distance/2 to infinity will all be sharp.  As you change the f-stop you’ll see it alter quite a bit.  So at f/4 it’s just over 9m in my example, at f/18 it’s just over 2m.  Which explains why landscape photographers like to close down the aperture – lots of acceptably sharp bits of greenery.

So what about us wildlife photographers?  The good news is that, for much of the time, you can almost forget about Depth of Field.  That’s because a lot of our subjects are not that close and are pretty small.  This Turnstone for example was rootling around at an 11m distance.  Plugging the relevant numbers into my calculator gives me a DoF of 15cm – plenty enough to get the little Turnstone acceptably sharp, even with the lens wide open.

Larger animals at a distance?  DoF is around 2m for these Koniks (again wide open), so no issues.

However, if I try and use the same camera/lens combination on a close-up Konik, I’m in trouble.  Lots of this image is out of focus (DoF is only about an inch ) – but does it matter?  The whole point of the image was not to get it all in focus, it was to make a joke about the impossibility of shooting birds when the Koniks were being friendly – and the ear is acceptably sharp, so it works.

So in many ways we’re lucky shooting wildlife.  With few DoF limitations we can shoot wide open (allows us to get the shutter speed up, or shoot in lower light, both very handy).  When it does become an issue for us is with bugs and macro shooting.

At macro and closeup distances, your DoF can be very thin.  Even at f/13, the DoF on this little spider is just 3.5mm – you can see how quickly the image blurs in front and behind the focal point.

That can be a real problem when shooting tiny beasties.  The only options you have are to close the lens down even more – though you’ll need good light, maybe using a flash to get lots of close up illumination.  Sometimes you can move around a little bit to get the subject at a shallower angle – front on this Wasp Spider would be next to impossible to get all in focus, but from the side it’s much easier

Or you just have to accept the limitations and live with the fact the body is out of focus as long as the face is sharp, as with this Beewolf

It is possible to use a technique called Stacking to get better DoF.  Essentially, you take multiple images, each with a slightly different focus point and then use software to blend all the images together into one, fully focussed image.  Unfortunately, this works best with inanimate or dead subjects – something that won’t move in other words!

The final approach is to leave the DSLR at home and use your phone instead.  The small sensors used in phones (and various point & shoots) tend to give rather deep depths of field.  This makes them less desirable for portraits (where people like a nice blurry background) but great for bugs!

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Find me on Flickr / All about your camera - The Getting off Auto Index

  • Another excellent addition to the GoA thread so many thanks WJ;   I've had a quick read through but will go read in more detail after I've taken my kitchen apron off  LOL     I love the way getting correct DoF makes the image really stand out, almost 3D in many cases and eradicates any distracting/ busy backgrounds that we often encounter.    I've never tried stacking although promised I would try it one day -using a solid tripod and probably my 100mm macro lens.  

    So much still to learn with a brain that's slowing down with age  LOL    Once again WJ,  many thanks for the time and effort you put in to this thread which I find of enormous interest and help and a thread i have permanently bookmarked.      

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    Regards, Hazel 

    "Each kindness shown to birds or men is sure to flutter back again" 

  • Great stuff, WJ. Very interesting and informative as always.

    Whistling Joe said:
    It is possible to use a technique called Stacking to get better DoF.  Essentially, you take multiple images, each with a slightly different focus point and then use software to blend all the images together into one, fully focussed image.

    I follow someone on Flickr who uses complicated rigs for taking precision shots of insects for stacking. A lot of work I suspect, but the results are incredible (here).

    My bird photos HERE

  • In reply to Paul A:

    Thanks WJ, most interesting. My selection of f-stop for depth of field is a bit hit and miss so it's good to see the theory behind it.

    As a matter of interest which App do you use to calculate it. On Google Play I notice there's one called HyperFocal Pro.

    The problem I see is that by the time I'd done the calculation the bird would have flown - literally.

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    Regards,Tony

    My Flickr Photostream 

  • In reply to TeeJay:

    A fine article.

    As you say, it's often OK for wildlife, unless you're very close, which is lucky as we can't always adjust the light to accommodate small apertures or slow the shutter speeds without introducing motion blur, but hyperfocal distances can be very useful for landscapes, especially those taken from a low angle.

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    Nige   Flickr

  • In reply to TeeJay:

    TeeJay said:

    As a matter of interest which App do you use to calculate it. On Google Play I notice there's one called HyperFocal Pro.

    The problem I see is that by the time I'd done the calculation the bird would have flown - literally

    The App I have is simply called DoF Calculator - the icon is the front of a lens (if that helps).  I've not sampled a lot of Apps, I found that one and it worked for me so kept it.  I wouldn't embed its use into all your shot taking, but it's a useful aid to help understand DoF - and perhaps most importantly - when to chill out and not worry about it :-)

    Paul A said:
    I follow someone on Flickr who uses complicated rigs for taking precision shots of insects for stacking. A lot of work I suspect, but the results are incredible (here).

    Yes, I've seen his work before - amazing what you can do if you put your mind to it!  Like Hazy, I keep promising to give it a go, but the time isn't easy to find :-)

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    Find me on Flickr / All about your camera - The Getting off Auto Index

  • Superb photos WJ and brilliant examples of DoF.

    Most of the time, my Canon 750D is off auto and I tend to work between TV (exposure priority) and AP (aperture priority).

    The times when I use AP are for landscape, while most others I opt for TV. I guess I should experiment more with some of the other settings, like the macro and sport modes, though I often find TV or AP will give my the background I need. With many DSLR's today, using a fast shutter and multi-shot setting, that will enable good sport images, often with better focus over the sport settings, because I can opt for whatever spots for the camera to focus on.

    One thing you don't seem get today on digital cameras, which many old film SLR or medium format cameras had, was a depth of field preview button/lever, which operated the diaphragm to enable the photographer to see the image before pressing the shutter.

    I know with todays digital cameras, you can waste shots at no great expense, which was a dilemma with film, you had to hope you got the results you wanted, and bided your time waiting for the film to be developed. But it is a feature I actually do miss.

    There is another plus with the DoF preview, when the lens is away from the camera, you can show would be students how the DoF diaphragm works.

    For those who are sceptical about GoA, with today's digital cameras, the cost really is only time, so just go for broke, try the manual settings and if time and subject(s) allow, do both and when you get home, enjoy your results, whatever they are. Even the bad ones in your eyes, are good in some way, and remember, failure only occurs when you give up.

    Those where you didn't quite get the results you desired, are a learning curve, try again by varying the settings either side of the attempted shot.

    Mike

    Flickr Peak Rambler

  • In reply to Mike B:

    Good comments Mike.  I'd be surprised if there isn't a DoF button on the 750D (though I haven't gone to find the userguide to check).  There certainly is on the older 700D (just below the lens release button) as well as all the larger bodies I use (80D, 7D2, 5D3).

    I wouldn't worry too much about the other settings you mention - they're just there to help people moving up from something more basic without the experience you already have.  Sport mode is simply going to prioritise a higher shutter speed to freeze action for example.  When you get into the more expensive bodies, you lose those anyway - I guess the manufacturers assume you will have a bit more experience before spending such a large amount :-)

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    Find me on Flickr / All about your camera - The Getting off Auto Index