rmalarz Loc: Tempe, Arizona

I guess that's why lens manufacturers place scales indicating the depth of field on lenses where the scale "expands" towards the infinity mark. They must have been hoodwinked into believing the 1/3-2/3 relationship all these years.

Don't be misled by one particular focusing method, and one that is probably rarely used by the average person on UHH. I find it interesting that one can latch onto one rule of thumb as if it were provided by divine intervention and try to refute another rule of thumb that, in general use, provides a close enough estimate.
--Bob

selmslie Loc: Fernandina Beach, FL, USA

If you believe that then you are not paying attention or you don't understand DOF.

Maybe you could learn something from a DOF calculator or from What is wrong with Depth of Field and Hyperfocal Distance?

N4646W

Why? Every lens and camera situation is different, the distance to subject is different, environment is different. It gets you within the ball park, and you can adjust from there for your specific gear. I have lenses that are way better than the published DOF charts, others fall short, but it also depends on which camera I use them and how much I want to (think anal) pixel peep. To throw another monkey wrench into the mix, what about the hardware and software used? I certainly do not have the sophisticated software and hardware used to determine these results that labs use.

For me,DOF charts are usefull if you are trying to decide between lenses type from different manufacturers. Is it worth spending the money for this X lens or will Y do the same thing for what I do.

I hope this does not come across as an offensive or argumentative reply, but as another way of looking at supposed bench marks. In the real world bench marks go out the window for the most part.

Still, I don't think we have resolved "why" the OP asked his question. I personally would like to know what prompted him.

rmalarz Loc: Tempe, Arizona

I'm quite acquainted optical characteristics including, but not limited to DOF.
--Bob

selmslie Loc: Fernandina Beach, FL, USA

Apparently not.

So why the statement about engraved DOF marks having anything to do with 1/3-2/3?

All you need to do is look at one of those lenses. There is no such relationship!

rmalarz Loc: Tempe, Arizona

Really!!?? Have you looked at the DOF scale on a lens lately? The markings increase in distance as one approaches the infinity end of the scale. I'll bet if one looks at the distance indicated on the near side of the focus mark vs. the distance on the far side of the focus mark, the distances will, more than likely, be 1/3:2/3.

I shall examine this hypothesis more closely when I return to my laboratory later this evening.
--Bob

Longshadow Loc: Audubon, PA, United States

Still a rule of thumb.
Rules of thumb are not steadfast in their meaning, only guides, like the rule of thumb for taking images of stars. May vary per camera.

selmslie Loc: Fernandina Beach, FL, USA

DOF is primarily defined by film or sensor format, focal length, aperture and focus distance. But other factors matter.

Take a look at the DEPTH OF FIELD CALCULATOR

Focus at 40 feet: 17.49 in front, 139.45 behind - nearly 1:8, not 1:2

(Download)

Focus at 2 feet: 0.07 in front, 0.07 behind - 1:1, not 1:2

(Download)

Longshadow Loc: Audubon, PA, United States

I have two DOF calculators that I sometimes use. They're handy.

selmslie Loc: Fernandina Beach, FL, USA

You would lose that bet as I just showed.

For starters, take any full frame 50mm lens and place the infinity mark at the f/16 mark. You will find the focus point at around 16 feet (the hyperfocal distance) and the near DOF mark over the other f/16 mark at around 8 feet. The calculated DOF would be somewhere between 1390 to infinite.

That's not 1/3-2/3 (1:2). It's closer to 8:infinity.

(Download)

Dikdik Loc: Winnipeg, Canada

I nearly always place the far focus mark on infinity... an old photographer showed me that half a century ago.

Dik

Blurryeyed Loc: NC Mountains.

Smaller apertures will require a longer exposure time in any given available light, today's cameras will adjust the exposure time to properly expose. Smaller apertures will give a greater depth of field, but I am not sure that was your question, the premise of your question I think is wrong, the smaller aperture does not block light so much as it lets less light through from the entire scene which in turn requires a longer exposure time, the "out of focus" area should be exposed the same either way as well as the subject.

selmslie Loc: Fernandina Beach, FL, USA

Take it from another old photographer - if you do that your distant subjects will be at the far limit of the DOF and on the verge of looking blurry.

You also might learnn something useful from What is wrong with Depth of Field and Hyperfocal Distance?

Dikdik Loc: Winnipeg, Canada

The smaller aperture uses a smaller surface of the lens where the angle of the glass surface to the incident light is less; the depth of field is greater.

Dik

N4646W

May I ask what information prompted you to ask this question? That way maybe we can get your topic back on track. Hopefully someone can help with out hijacking your thread.

Ron