Using hyperfocal distance focusing

Rooster

Rooster

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John
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I've been reading about hyperfocal distance focusing and I'm keen to give it a go next time I'm out. My usual method is the old "focus a third of the way in" rule of thumb. Basically if I'm using a narrow aperture like f/18 then as long as the foreground is sharp the background can take care of itself. It's a bit hit or miss, it's usually good enough but I've marred some good landscapes by having soft background details.

So I've got an iphone app called Photocalc. You put in the focal length and aperture and it tells you the distance you should be focusing at. Eg 17mm using f/18 the hyperfocal distance is apparently 1 foot 9 inches. Now my lenses have distance scales but they're nowhere near that precise. There's little distance between the 1 metre mark and the infinity mark. Do I take a tape measure, measure out 1' 9", stick my thumb out there and focus on it manually or what? Or is it not so precise, as long as the focus is somewhere around that distance it'll be ok?

A mate of mine says not to bother as it results in everything being somewhat in focus but nothing really pin-sharp. Is he just doing it wrong? I suppose sharpening up the foreground would sort that problem out?
 
At f/18 it probably doesn't matter because everything will be softened by diffraction.

Anyway, if you want to use the hyperfocal technique you don't need to be that precise. Your app is telling you that if you focus at 1'9" then everything will be in focus from there to infinity. But if you focus at 2 feet, or 3 feet, or wherever, then obviously everything from there to infinity will be sharp. If it really matters to you to have an object 2 feet from the lens in focus, then focus on it; otherwise you'll be OK.

Note, however, that if you focus at the hyperfocal distance then by definition the far distance is right on the limit of the zone of "acceptable sharpness". Trouble is, that word "acceptable" hides a multitude of assumptions and what's acceptable for one person might not be acceptable for another. To my mind it's better to play safe and focus a bit beyond the hyperfocal distance.
 
Given that for f/5.6 the hyperfocal is about 2m at 17mm on full frame (about 3m on APS-C), I haven't a clue why anyone would use f/18 and risk compromising image quality through diffraction.

Hyperfocal and DoF calculaters are handy tools in the field, but they're very easy to use badly if you don't once in a while have a look at a full DoF Table. If you don't have anything in the frame as close as 21" then being absolute on the distance isn't critical. Focussing on anything beyond the hyperfocal distance will also give focus to infinity and the only difference will be how far in front of the focus point is also acceptably sharp.
 
Rooster said:
A mate of mine says not to bother as it results in everything being somewhat in focus but nothing really pin-sharp. Is he just doing it wrong? I suppose sharpening up the foreground would sort that problem out?
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Id agree with him, Hyper focal 2/3 stuff is a useful tool, especially as a beginner, but if you really want to control what is and isn’t pin sharp -against what is and isn’t a reasonable sharpness. then go directly to actually focusing on foreground and from that calculate and know what the sharpens will be all the way to the back of your scene, rather than relying on possibly slightly less pin sharp ends of a hyper focal range.
 
Rooster said:
...A mate of mine says not to bother as it results in everything being somewhat in focus but nothing really pin-sharp. Is he just doing it wrong? I suppose sharpening up the foreground would sort that problem out?
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People do say rather silly things like that, but if you take that view then what you are saying is that the concept of depth of field doesn't exist and that the only time anything is ever pin sharp is when you are focused directly on it. Which seems a bit foolish to me, and certainly not very helpful.

Depth of field calculations directly address the question of what exactly is 'pin sharp'? Which is, the finest level of detail that can be detected by the human eye in a print when viewed from a normal distance, and normal distance being defined as the length of the diagonal. So if you take a 10x7in print an view it from a distance of about 12in, or maybe an A4 magazine size page at 15in, then there will be certain level of detail beyond which you cannot see.

That is 'pin sharp' and it is pointless having any finer level of detail than that if you can't see it. DoF calulations take that limit of visual acuity and turn it into a set of tables that give a wide range of settings that can be used to ensure that all detail is always kept within that limit.

If you stick to the rules about print size and viewing distance, the DoF calcs always work perfectly, but often people make quite big prints of a favourite shot and, naturally enough, want to look at them quite closely. If that's the case, then you can tighten up the DoF standard yourself just by setting a higher f/number than the one suggested, like f/8 instead of f/5.6. Or you can tweak the focus setting.
 
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