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How do you 'focus into' a scene?
I've been reading some books for beginners, and the phrase that I'm having trouble with is "focus 1/3 of the way into the scene". I'm sure that I'm just dumb, but I can't find an explanation of this. Does this mean, for example, if my subject is 9 feet away, that I manually set the focus ring on the lens to focus at 3 feet? It seems to be related to depth of field considerations, but I don't understand it...

Comments (6)

If there's a clear "point of interest" somewhere less than a mile away, focus on that thing. Don't even consider the 1/3-into-the-scene suggestion..

If there's no particular point of interest, and you want it ALL in reasonable focus, which is often the case in landscapes or architectural shots, then use this rule-of-thumb. Reduce the aperture (bigger numbers, e.g., f/16). Aim at a detail on the ground or some other object that is about a third of the distance between you and the farthest object you can recognize. Then recompose to include the whole scene and shoot..

Let's call the arbitrary "detail on the ground or some other object" the POI. As the aperture gets smaller, more things get into focus in front of the POI, and also behind the POI. More space behind the POI gets into focus. This is the reason for the 1/3-into-the-scene suggestion..

As a suggestion, it's up to you to decide if it applies and if you wish to try it..

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/..

Comment #1

Normally, your depth of field for any given aperture is going to be 1/3 in front of your focus point and 2/3 behind your focus point. If you're shooting wide open, then you may not have enough depth of field to worry about. But if you're shooting at f8 or above, then we might be talking about a more significant amount of space. If you focus on the front edge of your subject, then you're not using all of your depth of field because part of it is falling in front of where you focused and is not being used. So by focusing slightly farther back (or 'into' the scene), you can now use that 1/3 of your depth of field that's in front of your focus point to get your foreground in focus and let the remaining 2/3 of your depth of field that's behind the focus point help get your background into focus. Is that all clear as mud now? lol..

Comment #2

Thanks, Ed, that clears it up nicely. It seemed like the books that I was reading assumed that the reader would understand this even though they explained a myriad of other concepts..

Thanks again...

Comment #3

This rule is very important in group shots with more than one row of folks.If you focus on the front row you may not have backrow completely in focus..

Just a note if you have an especially wide group you need to bring the ends of the group in because they will be further away than the middle of the group, just a tip.Let the light in!.

Comment #4

TaoMaas wrote:.

Normally, your depth of field for any given aperture is going to be1/3 in front of your focus point and 2/3 behind your focus point. Ifyou're shooting wide open, then you may not have enough depth offield to worry about. But if you're shooting at f8 or above, then wemight be talking about a more significant amount of space. If youfocus on the front edge of your subject, then you're not using all ofyour depth of field because part of it is falling in front of whereyou focused and is not being used. So by focusing slightly fartherback (or 'into' the scene), you can now use that 1/3 of your depth offield that's in front of your focus point to get your foreground infocus and let the remaining 2/3 of your depth of field that's behindthe focus point help get your background into focus. Is that allclear as mud now? lol.

I read somewhere that the 1/2 - 2/3 rule you mention is not in fact universally valid: the proportions in focus in front of/behind the thing you focus on varies according to the distance of your target object. For a landscape shot it's more likely to be around 50/50..

(If I weren't already late for work I'd find the source of that info   ).

Tim..

Comment #5

TaoMaas wrote:.

Normally, your depth of field for any given aperture is going to be1/3 in front of your focus point and 2/3 behind your focus point..

This is a myth, often repeated but incorrect..

Try putting some numbers into the depth of field calculator at http://www.dofmaster.com/dofjs.html.

For example - 40D sensor size, 50mm, f/4, 100 feet 4% in front, 96% behind..

Another - as above but focused at 2 feet 49% in front, 51% behind...

Comment #6

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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