Depth of field? What depth of field?

Giving your images a distinctive and interesting look is always a challenge but there are several tools available.  Depth of field is a popular “art” tool that enables you to quickly bring the viewer’s eye to the exact subject you want them to pay attention to right from the start.  To use effectively, though, you need to understand what is the depth of field you’re going to get for your composition?  It’s a tricky question – each lens behaves differently based on aperture, distance from subject, focal length, etc.  You almost have to experiment with your bag of lenses and learn.  Or  you can look up the depth of field chart for your lens and memorize it.  My problem with the latter option is I have a hard time visualizing what a 3 inch depth of field or a 500 foot depth of field looks like.  I usually just play around with my lenses and see what they deliver.

It’s especially daunting with telephoto lenses.  The depth of field for these starts out short and seems to only get smaller.  Here’s an example:

I liked the little snowball sitting in the sunlight so I wanted to make an image of it.  I was sitting at a picnic table with my camera on my tripod, using my 300mm manual focus Olympus lens (from the OM film camera days).  On my digital Olympus body this is equivalent to a 600mm lens on a full format camera.  I’m about 10 yards from the snowball so this long lens really gets up close.  I think the aperture was around f/11 or f/16 since I was looking for maximum sharpness.  Notice the area that’s in focus – it’s a narrow band where the snowball is in the sunlight.  The grass in the foreground and snowbank in the background are completely out of focus.  Which is what I wanted – you eye should go right to the snowball.  But how much depth of field is really there?

100% crop from previous image

100% crop from previous image

If I zoom in on the image you can see the depth of field is REALLY narrow; according to one online DOF calculator it comes in at 4 inches.  Which means if I was making an image of a deer’s face using this distance and settings, their eyes would be in focus but their ears and nose might not be – and this is at a small aperture (not that I expect to be 10 yards from our local deer, at least not unless I’m holding a handful of corn for them).  It does give a cool look, though, as it centers your eye right on the subject I want you to pay attention to.  Like most specialized tools – and a long telephoto lens is definitely that – you get the best results when know the lens’ limitations and operating within them.

In my youth as a photographer I was always trying to get maximum depth of field, especially with landscapes.  I’ve learned now that shortening it up can truly bring some interesting features to your pictures.  Just have to know when and how to use the technique effectively and what tools work best to deliver on it.

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4 thoughts on “Depth of field? What depth of field?

    • Sharp images from long lenses are generally a function of two things – eliminating shaking/movement and using good glass. Two ways to eliminate shaking/movement. 1. use a shutter speed at least the reciprocal of your focal length – example, 300mm lens use at least 1/300th second. I usually double that when I can so a 300mm lens uses 1/600th second. If you run out of aperture (depth of field gets too short) increase the ISO to get the shutter speed/aperture combination you need for the exposure. 2. use a sturdy tripod – I’ve stopped trying to handhold a long lens unless I’m trying to follow a complex motion and even then I usually get blur. Put the camera/lens on a tripod and use the mirror lockup on your DSLR to eliminate that little vibration. Some cameras call it mirror lockup and some call it vibration reduction – check your manual. Using good glass is a function of economics – better glass generally costs more although my 300mm lens is an old manual Olympus model I use with an adapter on my digital body. Total cost of lens and adapter was less than $400 whereas the digital version of Olympus’ 300mm lens is $7000. I’ve tested them side by side and for landscapes (where nothing is moving) the level of sharpness is equivalent. If you can rent some long lenses and see which give you the result you want before buying. You can buy good used equipment from several sites – I use http://www.keh.com.

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      • Thanks melmann. I shall make a note of this. It’s just that whenever I use my good lenses, I can’t seem to get rid of the focus. I want to sometimes take a picture with focusing, without any blurriness, but I can’t figure it out. Well, thanks again. I never knew the glass is also something to consider. I also didn’t knew about mirror lockup.

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      • There are theoretical limits on the sharpness any one lens will deliver but most problems with lack of sharpness are caused by the photographer! Try hand holding to make multiple versions of the same image with your long lens, gradually increasing the shutter speed and see where your blur starts going away or decreasing (zoom in to 100% on your computer). Then do the same exercise with a tripod and see if that gives you even less blur. If you have image stabilizing lenses check your manual to determine whether that should be turned off when the lens is on a tripod – sometimes that will cause blur as the lens fights the tripod to stabilize the image.

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