Spring 2012

Spring 2012
by ani

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In an earlier question, several people suggested that for landscape photography, you want a small aperture, “to maximise the depth of field”.

I'm not sure I understand that… Surely if you're photographing a landscape, the lens will always be focused “at infinity”, so 100% of the scene will always be in focus, regardless of aperture.

Or am I misunderstanding how aperture works?

(I thought the further away something is, the greater the depth of field. So when an object is three and a half miles away, it's going to have a huge depth of field!)

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It depends whether or not there is a foreground that you want to be in focus as well as the distant background. – Count Iblis Feb 15 at 18:43
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The lens is not always focused at infinity for Landscape photography. If that was the case, a 17-35mm lens would come without a focus adjustment; right? I think your idea of what is Landscape photography should be reconsidered, it seems to be too narrow currently. – dpollitt Feb 15 at 18:47
    
Hmm, OK. So it seems the misunderstanding revolves around exactly what one defines as a "landscape" photo... – MathematicalOrchid Feb 15 at 20:00
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In fact, actually focusing at infinity is wasting depth-of-field; if you focus at the nearest point that still gives acceptable focus (blur comparable to the pixel/grain size) at infinity, called the hyperfocal distance, you get a lot more near depth because you're not wasting some of the capacity of the lens focusing things "beyond infinity". – hobbs Feb 15 at 20:15
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I think you know this, but in case it isn't clear to anyone else reading your question, "focused at infinity" does not mean "everything is in focus". Read What is “infinity focus”? for more. – mattdm Feb 15 at 22:22
up vote 17 down vote accepted

Or am I misunderstanding how aperture works?...I thought the further away something is, the greater the depth of field. So when an object is three and a half miles away, it's going to have a huge depth of field!

You're not wrong about that, but landscape photography often involves more than just photographing very distant objects. You often have objects at a range of distances, like flowers up close with trees in the middle ground and a mountain range behind them. In a portrait, you want to (literally) focus on the subject, so bokeh that reduces everything else to a lovely blur is welcome. In a landscape, you usually want someone to feel like they're taking in an entire vista -- everything should be sharp. If there's any blur, it should be intentional motion blur due to a long exposure. And you don't always focus at infinity -- you want to focus close enough that both foreground and background will be sharp.

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11  
One point to consider on that - when you look at a vista in the real world, everything you look at is in focus. Your eye darts to that tree? in focus. Over to that flower? In focus. That mountain in the background? in focus. Sure, everything else is out of focus when you look at the tree, but you don't notice that. It is only when you are focusing on one and only one thing in the view (rather than darting around the vast scene) do you kind of notice other things not being in focus. – user13451 Feb 15 at 19:32

In addition to increasing the depth of field in order to keep everything in focus, many lenses are also less sharp at wider apertures. Landscape on digital is best shot in the range of f/5.6 to f/11. Anything wider (faster, smaller number, bigger aperture) than f/5.6 will start to "soften" the image, and anything narrower than f/11 will lose definition to diffraction.

The main advantages to using a wider (faster/smaller number/bigger opening) aperture are:

  • Let in more light to reduce the exposure time, to reduce the effects of camera shake, subject motion, and low light
  • Limit the depth of field in order to have subject in focus and background out of focus (better subject isolation)

Disadvantages of using wide aperture:

  • Details are less sharp
  • Subject can be out of focus

The advantages of using a narrower (slower/bigger number/smaller opening) aperture are:

  • Better lens sharpness
  • Larger depth of field - capture both close and distant subjects in focus

Disadvantage to narrow apertures:

  • Requires longer exposure time for equivalent exposure, so subject or camera movement can cause blur
  • Poor subject isolation - the background being in focus might reduce artistic quality of image

As landscape is generally not moving, and often mounted on a tripod, having a fast shutter speed isn't important, so you can use a smaller aperture in order to get sharper images.

You can test this yourself - set your camera aperture priority, point it at a still subject and take two pictures - one at the widest aperture setting on your lens, and one at f/11. Blow them up on the computer and the difference will be apparent in details.

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The ideal aperture will also depend on the sensor size (crop factor). For a given FOV, the ideal aperture is approximately a constant absolute size, and the f stop will therefore change with focal length. For example, if I shoot at f/5.6 on my Nikon DX system, I'll get close to the same results by shooting f/8 on an FX or 35mm system, f/16 on my RZ67, or f/32 on my 4x5 (although the 4x5 gives more focusing options). It has little to do with digital versus film. – Dietrich Epp Feb 15 at 23:18
    
Good point - I suppose that when I say "digital" I just mean in the range of typical DSLR sensor sizes. – Tim Gostony Feb 15 at 23:49
    
Diffraction only begins to be detectable at the DLA of a sensor when viewing an image close enough at 100% to perceive individual pixels. As with many things in photography, viewing size/distance affects when it actually becomes noticeable. And there are some lens specific post-processing tools that can reduce the effects of diffraction. They take a healthy dose of processing power and can make large raw files huge, but they work. – Michael Clark Feb 16 at 1:26

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