DOF .. 1/3 front, 2/3 behind?

Still True? Modern era expectation? Old school? .....?

This is just a rough estimate... the 1/3 and 2/3 rule of thumb.

It's an optical thing, DOF.

It makes no difference, old school or modern... daguerreotype, glass plate, sheet film, roll film, or digital... DOF actually is the same.

DOF is shallower or deeper depending upon lens focal length and distance to the subject. Large, medium or small format, be it analog or digital, makes no actual difference so long you use the same focal length and stand the same difference from the subject. However, we rarely use the same focal length or distance to the subject, after we change format. We tend to change focal length and/or move closer to or farther from the subject to better accomodate a different format, so in real practice DOF changes.

But the approx. way it falls doesn't change... it will always be roughly 1/3 in front, 2/3 behind.

Check out the illustrated example partways down the page at http://www.dofmaster.c​om/dofjs.html With a lens focused at ten feet and an aperture that gives 6.61 feet of total DOF, appprox. 2.21 feet of that is in front of the point of focus, while approx. 4.2 feet of that total DOF falls behind the point of focus.

BEFORE USING THE DOF MASTER SITE MENTIONED ABOVE, READ THIS:

https://photography-on-the.net …p?p=15249487#po​st15249487

The DOF Master site was declared clean quite some time ago but the warning message was posted for 30 days auto-expiration. Thus it will remain for another 10 days (more less). You can see what Google has determined on any site by using the URL http://www.google.com …iagnostic?site=​domain.tld but replace the domain.tldwithe the domain of the site you desire info about. In other words go to http://www.google.com …ic?site=www.dof​master.com and Google will report back the following:

■What is the current listing status for domain.tld?
■What happened when Google visited this site?
■Has this site acted as an intermediary resulting in further distribution of malware?
■Has this site hosted malware

As the focus distance approaches the macro range, the depth of field will be equally spaced before and behind the subject. Ratio = 1:1

As the focus distance approaches the hyperfocal distance, the depth of field behind the subject will become progressively bigger than the depth of field before the subject. This makes sense when you consider that at the hyperfocal distance the DOF in front of the subject is finite and behind the subject it is infinite. Infinity / finite # = infinity.

So at some middling range the DOF behind the subject will be a little bigger than in front of the subject. Thus the quite general rule of thumb.

John from PA wrote in post #15330477
The DOF Master site was declared clean quite some time ago but the warning message was posted for 30 days auto-expiration. Thus it will remain for another 10 days (more less). You can see what Google has determined on any site by using the URL http://www.google.com …iagnostic?site=​domain.tld but replace the domain.tldwithe the domain of the site you desire info about. In other words go to http://www.google.com …ic?site=www.dof​master.com and Google will report back the following:

■What is the current listing status for domain.tld?
■What happened when Google visited this site?
■Has this site acted as an intermediary resulting in further distribution of malware?
■Has this site hosted malware

Thanks for clearing that up John. I was just bringing the post to the OP's attention.

the problem i have is unless were focusing on something totally flat and perpendicular to the sensor, the AF will always focus closer to the camera because thats the way canon programmed it. The big AF square will lock at the first opourtunity it can grab anything. So if your photographing a full body portrait, the AF square covers the whole face, youre esentially focusing on the guys nose and losing a substantial amount of depth. So in this respect i would say the focus depth is in reality more in front than it is behind. This is why i wish my 60D had MFA, i would set it to back focus slightly when shooting full body portraits.

Just how big is your AF box? I think you're missing a point. If you are far enough back to be able to get the whole body in, the DoF is not going to be that shallow. Everything from the tip of the nose to the eyes will be in focus. I think you would be insane to MA something in the manner you are talking about.

As to the 1/3f and 2/3b, it depends. Like another one said, it will approach 50/50 depending on distance to subject, etc..

Or focus lock on their ear???

But Gregg is right. If you are taking a whole body portrait the difference between focusing on the tip of their nose or their eyes is not going to make any difference.

John

Gregg.Siam wrote in post #15332778
As to the 1/3f and 2/3b, it depends. Like another one said, it will approach 50/50 depending on distance to subject, etc..

Precisely this is the result as what i described. Close up you can nail the focus dead on the eyes hence the 1/3 front and 2/3 behind. At a distance you cant nail the eyes as the AF point rather grabs the nose or whatever it is thats closer like the brow or a protruding finge ect which gives you the 50/50.

^? As you get further away from a subject your dof is going to increase so if your AF point "grabs" the nose then their eyes are still going to be in focus.

Take your 17-50 for example. To get a full body shot at 50mm with your 60D you are going to need to be almost 4 meters away from your subject at the very least. At that distance your 2.8 lens will have a total dof of 68 cm or 31 cm in front and 37 cm in back of where your focus point locks..... so unless their eye sockets are really really deep that should be enough to get their eyes in focus even if you focus on the very tip of their nose!

Now if you want to zoom in at 200% crops and look at your images... all bets are off. Which brings us back to the OP's question. The 1/3-2/3 "rule of thumb" had to do with acceptable focus. It was never a exact measure of how in focus an area would be. Today it still applys if you use some common sense when looking at your images. (Get your nose off the computer screen!)

jwp721 wrote in post #15332962
^? As you get further away from a subject your dof is going to increase so if your AF point "grabs" the nose then their eyes are still going to be in focus.

The eyes will be acceptably in focus but the nose will be optimally in focus. And 50% of your optics are working on the fresh air infront of the subject. Doesnt it seem like a waste to you?

jwp721 wrote in post #15332962
Take your 17-50 for example. To get a full body shot at 50mm with your 60D you are going to need to be almost 4 meters away from your subject at the very least. At that distance your 2.8 lens will have a total dof of 68 cm or 31 cm in front and 37 cm in back of where your focus point locks..... so unless their eye sockets are really really deep that should be enough to get their eyes in focus even if you focus on the very tip of their nose!

so would you agree then that what i say is atleast relevant to making pictures of a horse or an ape... Or some peoples inlaws?

boerewors wrote in post #15333218
The eyes will be acceptably in focus but the nose will be optimally in focus. And 50% of your optics are working on the fresh air infront of the subject. Doesnt it seem like a waste to you?

Not if that is the effect I am going for... right now I am looking at a head and shoulder portrait I took where the subject's eyes and nose are in focus yet the back of her shoulders are slightly out of focus due to the dof. If I didn't want that effect I would have used an fstop of f-8 vs the f-4 that I selected.

boerewors wrote in post #15333218
so would you agree then that what i say is at least relevant to making pictures of a horse or an ape... Or some peoples inlaws

If I were taking a full body shot of a horse I doubt the fact that I focus locked on the tip of the nose would cause the eyes to be out of focus (would need to run the numbers but I doubt you would get into too much trouble unless you got down to f1.8 or f1.4). As far as inlaws that might be another issue.

Again it is all about acceptable focus and today's expectations.