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Warning in advance: this might get a bit boring 
So, in a quiet moment during my lunchbreak I decided to knock up a quick hyperfocal distance table for my camera, to print out and keep with me when I'm shooting landscapes. As many of you will know - and use - focusing your camera at the hyperfocal distance (which for any given camera/sensor varies according to focal length of the lens and the f/stop chosen) means everything from half that distance (i.e. half way between the lens and the hyperfocal distance point) all the way back to infinity should be "in focus". Just to elaborate for anyone unfamiliar with this, let's say you're using my Pentax K5 with an 17mm wide angle (this combo will be our "kit" for the rest of this monologue, by the way). At f/8, the hyperfocal distance would be 1.82m, meaning everything which is further away than 91cm from the lens should be in focus. Bonzer!
Now that got me thinking a bit more... I rarely shoot these sorts of shots from ground level - instead the camera is on a tripod, perhaps somewhere between 50 and 150cm from the ground. Using this 17mm wide angle lens, the field of view might be about 50 degrees or so vertically, which means the ground at the very bottom of the frame (i.e. nearest point I can see in picture) would still be over 1m away horizontally (if the lens is only 50cm above ground level) and well over 2m away if the camera is 1m high (which is still only about waist height even for a shortarse like me) So given everything from 91cm onwards at f/8 should be in focus, everything in frame should be in focus as long as my camera is at least about 40cm off the ground... and my tripod doesn't even go that low!
So all this fuss about using f/11 or f/16 (on a crop sensor)... is that unnecessary if we're shooting pictures of lakes, beaches and the like? Well, maybe not... because the calculation above makes a fair few assumptions:
1. We're shooting the camera perfectly horizontally - unlikely for most shots where we might choose to have 1/3 sky : 2/3 land (for example), i.e. pointed more "into the ground"
2. I can't focus "by distance" that accurately using the scale on my lens - I can hit 1m or 3m give or take as there are markings for those distances, but 2m or 2.5m? Especially given it's a sort of logarithmic scale...
3. We might be using wider angle or longer focal length lenses... this will definitely make a difference
4. Other people might not be using a Pentax K5 - what about full frame or even medium format (as well as MFT)?
Well, dealing with each of these complications in turn:
1. With our wide angle, we're actually only pointing our camera down by up to 10 degrees to get about 1/3 sky in the picture. After doing some trigonometry (which might well be wrong - it has been a while!) it seems this composition adjustment has the effect of reducing the distance of the nearest point of the ground in frame by about 25% for a telephoto or up to 30% for an UWA. So, if we're shooting at waist-height (1m) from the ground, this means the nearest bit of the ground to us that we can see in frame with our 17mm lens is still 1.5m away.
2. Focusing difficulty: This is tougher... if we've just calculated in the point above that we want to have everything at 1.5m and beyond in focus, this means we need to be able to set the focal range to 3m (or slightly less) and then choose an f-stop which makes sure that the hyperfocal distance is not more than this. As it happens, on my WA lens, I have a scale marking for 3m so I can probably get it pretty close to 2.9-3.1m or thereabouts. Generally, though, I reckon it's a lot tougher than this to set focus reliably using the distance scale (at least on my lenses). I reckon there's an error of perhaps 25%... so we need to factor this in when working out what we can reliably set out aperture to and still guarantee F2B sharpness.
So what does this mean so far? Well, for my 17mm lens, with a composition 1/3 sky and 2/3 "land", I'm guesstimating my manual focus distance to be somewhere in the 2.3-3m range (I can probably do better than that, but let's be conservative), which will mean my foreground is definitely going to be in focus (we can, of course, check this is the case by looking through the viewfinder). So, taking the lower of this range (2.3mn), I want an aperture of f/6.3 or smaller to guarantee front-back-focus. Now, unless I move my camera further towards the ground, either by lowering the tripod or by pointing the lens more towards the group (i.e. increasing the 2/3 land proportion of the shot), there is NOTHING "landscapey" I can do with this 17mm lens which will require a smaller aperture than f/6.3 to guarantee front-to-back focus, assuming I get my focusing approximately right. Isn't this a bit surprising? So much for f/11. I might WANT a smaller aperture than f/6.3 because of a lens's sweet spot or because of high overall scene brightness, but it's not going to be driven by depth of field for landscape shots (macro's different, ok guys ).
3. What about longer or wider lenses? Well, the interesting thing is that the wider we go, the shorter our hyperfocal distance becomes for any given aperture, and although we're able to see ground closer to the lens (because of the wider field of view), the decreasing hyperfocal distance wins the "maths race" here. So, wider than 17mm? Well, you may be able to get away with an even bigger aperture (lower f/stop) than f/6.3 at 1m above ground. It's only when we start moving to longer focal lengths that we do need to be careful. With a 35mm lens on my crop sensor (so closer to a nifty fifty on 35mm) my nearest object should be further away at 3.3m, but that means a 6.6m theoretical HF distance and given the tiny throw on my focus ring between 3m and infinity, it's just guesswork setting the focus distance according to the scale. Of course, a quick chimp at maximum zoom should be able to confirm focus once you've set it. But anyway, we're talking f/10 or f/11 to get front-to-back focus using that lens. Once we start using longer telephotos still then we're well into diffraction territory and we're going to be losing sharpness somewhere, somehow. But how many landscape shots requiring F2B sharpness are really taken with long lenses? Some, yes, but not the vast majority.
4. Other sensor sizes and camera formats... well, this is easy. On my camera, a 15.7mm lens is the same f/l as the height of the sensor so let's switch for a moment from our notional 17mm lens used in the above example to an exact match for the sensor. At 1m from the ground and 1/3 sky, my nearest object is about 1.4m away so hyperfocal distance needs to be 2.8m or less (probably a touch lower still to make sure). This means I'd want f/6.3 to guarantee F2B focus for an UWA which is the same focal length as the height of the sensor. Switching to full frame (23.9mm), all the distances stay the same if we use a WA equal to the height of the sensor (24mm). The greater "circle of confusion" for the larger sensor, though, means we'd want to up to f/8 or perhaps even f/11 (to allow more margin for error in setting focus distance) to guarantee F2B sharpness. Of course, we have more latitude with full frame to stop down further before hitting diffraction problems. If we go wider than 24mm on full frame, we're just giving ourselves more headroom to play with.
Conclusions / tl;dr
Unless you are physically lying on the ground or shooting pretty much at the ground, there isn't any benefit (in terms of depth of field) of taking your WA lens past about f/8 for crop and f/11 for full frame with landscapes. There are always exceptions and if there is something big raised up from the ground which enters view much nearer than my calculations assume then, sure, you're scoobied. But, ignoring these fairly unusual extremes, you simply don't need to chase the aperture down with wide angle lenses to get sharp landscapes front-to-back.
If, however, you are not using a WA lens, then you might quickly find your image squashed between the blurry boundaries of diffraction and an inability to get front-to-back sharpness. If I want to take a nice layered hillscape perhaps with a big fat setting sun and have my camera 1m from the ground equipped with a 90mm zoom, I'm going to need f/32 to get full front-to-back sharpness (which is properly in diffraction-limited territory and also at the upper limit of my camera/lens). Alternatively, I could choose f/11 (with very little diffraction) and live with the water/land/midground from 8m (the nearest point in view) to 18m being out of focus.
Comments / thoughts / what have I missed?
So, in a quiet moment during my lunchbreak I decided to knock up a quick hyperfocal distance table for my camera, to print out and keep with me when I'm shooting landscapes. As many of you will know - and use - focusing your camera at the hyperfocal distance (which for any given camera/sensor varies according to focal length of the lens and the f/stop chosen) means everything from half that distance (i.e. half way between the lens and the hyperfocal distance point) all the way back to infinity should be "in focus". Just to elaborate for anyone unfamiliar with this, let's say you're using my Pentax K5 with an 17mm wide angle (this combo will be our "kit" for the rest of this monologue, by the way). At f/8, the hyperfocal distance would be 1.82m, meaning everything which is further away than 91cm from the lens should be in focus. Bonzer!
Now that got me thinking a bit more... I rarely shoot these sorts of shots from ground level - instead the camera is on a tripod, perhaps somewhere between 50 and 150cm from the ground. Using this 17mm wide angle lens, the field of view might be about 50 degrees or so vertically, which means the ground at the very bottom of the frame (i.e. nearest point I can see in picture) would still be over 1m away horizontally (if the lens is only 50cm above ground level) and well over 2m away if the camera is 1m high (which is still only about waist height even for a shortarse like me
) So given everything from 91cm onwards at f/8 should be in focus, everything in frame should be in focus as long as my camera is at least about 40cm off the ground... and my tripod doesn't even go that low!So all this fuss about using f/11 or f/16 (on a crop sensor)... is that unnecessary if we're shooting pictures of lakes, beaches and the like? Well, maybe not... because the calculation above makes a fair few assumptions:
1. We're shooting the camera perfectly horizontally - unlikely for most shots where we might choose to have 1/3 sky : 2/3 land (for example), i.e. pointed more "into the ground"
2. I can't focus "by distance" that accurately using the scale on my lens - I can hit 1m or 3m give or take as there are markings for those distances, but 2m or 2.5m? Especially given it's a sort of logarithmic scale...
3. We might be using wider angle or longer focal length lenses... this will definitely make a difference
4. Other people might not be using a Pentax K5 - what about full frame or even medium format (as well as MFT)?
Well, dealing with each of these complications in turn:
1. With our wide angle, we're actually only pointing our camera down by up to 10 degrees to get about 1/3 sky in the picture. After doing some trigonometry (which might well be wrong - it has been a while!) it seems this composition adjustment has the effect of reducing the distance of the nearest point of the ground in frame by about 25% for a telephoto or up to 30% for an UWA. So, if we're shooting at waist-height (1m) from the ground, this means the nearest bit of the ground to us that we can see in frame with our 17mm lens is still 1.5m away.
2. Focusing difficulty: This is tougher... if we've just calculated in the point above that we want to have everything at 1.5m and beyond in focus, this means we need to be able to set the focal range to 3m (or slightly less) and then choose an f-stop which makes sure that the hyperfocal distance is not more than this. As it happens, on my WA lens, I have a scale marking for 3m so I can probably get it pretty close to 2.9-3.1m or thereabouts. Generally, though, I reckon it's a lot tougher than this to set focus reliably using the distance scale (at least on my lenses). I reckon there's an error of perhaps 25%... so we need to factor this in when working out what we can reliably set out aperture to and still guarantee F2B sharpness.
So what does this mean so far? Well, for my 17mm lens, with a composition 1/3 sky and 2/3 "land", I'm guesstimating my manual focus distance to be somewhere in the 2.3-3m range (I can probably do better than that, but let's be conservative), which will mean my foreground is definitely going to be in focus (we can, of course, check this is the case by looking through the viewfinder
). So, taking the lower of this range (2.3mn), I want an aperture of f/6.3 or smaller to guarantee front-back-focus. Now, unless I move my camera further towards the ground, either by lowering the tripod or by pointing the lens more towards the group (i.e. increasing the 2/3 land proportion of the shot), there is NOTHING "landscapey" I can do with this 17mm lens which will require a smaller aperture than f/6.3 to guarantee front-to-back focus, assuming I get my focusing approximately right. Isn't this a bit surprising? So much for f/11. I might WANT a smaller aperture than f/6.3 because of a lens's sweet spot or because of high overall scene brightness, but it's not going to be driven by depth of field for landscape shots (macro's different, ok guys ).3. What about longer or wider lenses? Well, the interesting thing is that the wider we go, the shorter our hyperfocal distance becomes for any given aperture, and although we're able to see ground closer to the lens (because of the wider field of view), the decreasing hyperfocal distance wins the "maths race" here. So, wider than 17mm? Well, you may be able to get away with an even bigger aperture (lower f/stop) than f/6.3 at 1m above ground. It's only when we start moving to longer focal lengths that we do need to be careful. With a 35mm lens on my crop sensor (so closer to a nifty fifty on 35mm) my nearest object should be further away at 3.3m, but that means a 6.6m theoretical HF distance and given the tiny throw on my focus ring between 3m and infinity, it's just guesswork setting the focus distance according to the scale. Of course, a quick chimp at maximum zoom should be able to confirm focus once you've set it. But anyway, we're talking f/10 or f/11 to get front-to-back focus using that lens. Once we start using longer telephotos still then we're well into diffraction territory and we're going to be losing sharpness somewhere, somehow. But how many landscape shots requiring F2B sharpness are really taken with long lenses? Some, yes, but not the vast majority.
4. Other sensor sizes and camera formats... well, this is easy. On my camera, a 15.7mm lens is the same f/l as the height of the sensor so let's switch for a moment from our notional 17mm lens used in the above example to an exact match for the sensor. At 1m from the ground and 1/3 sky, my nearest object is about 1.4m away so hyperfocal distance needs to be 2.8m or less (probably a touch lower still to make sure). This means I'd want f/6.3 to guarantee F2B focus for an UWA which is the same focal length as the height of the sensor. Switching to full frame (23.9mm), all the distances stay the same if we use a WA equal to the height of the sensor (24mm). The greater "circle of confusion" for the larger sensor, though, means we'd want to up to f/8 or perhaps even f/11 (to allow more margin for error in setting focus distance) to guarantee F2B sharpness. Of course, we have more latitude with full frame to stop down further before hitting diffraction problems. If we go wider than 24mm on full frame, we're just giving ourselves more headroom to play with.
Conclusions / tl;dr
Unless you are physically lying on the ground or shooting pretty much at the ground, there isn't any benefit (in terms of depth of field) of taking your WA lens past about f/8 for crop and f/11 for full frame with landscapes. There are always exceptions and if there is something big raised up from the ground which enters view much nearer than my calculations assume then, sure, you're scoobied. But, ignoring these fairly unusual extremes, you simply don't need to chase the aperture down with wide angle lenses to get sharp landscapes front-to-back.
If, however, you are not using a WA lens, then you might quickly find your image squashed between the blurry boundaries of diffraction and an inability to get front-to-back sharpness. If I want to take a nice layered hillscape perhaps with a big fat setting sun and have my camera 1m from the ground equipped with a 90mm zoom, I'm going to need f/32 to get full front-to-back sharpness (which is properly in diffraction-limited territory and also at the upper limit of my camera/lens). Alternatively, I could choose f/11 (with very little diffraction) and live with the water/land/midground from 8m (the nearest point in view) to 18m being out of focus.
Comments / thoughts / what have I missed?