[clackers]

and dof exists along the same plane that focus does.

Geometry lesson for Osv ... a plane has no depth. ☺

[John Poirier]

There was me thinking this was a friendly forum..!
Can I sum this up?

- There is a peak of sharpness at the focal distance
- The sharpness drops off on either side of this distance
- The rate at which the sharpness drops off depends on a number of factors, but mainly on aperture...
- The point at which sharpness becomes unacceptable is very subjective and depends on subject, photographic style and purpose, and the viewer themselves
- DoF calculators assume an 'acceptable' level of sharpness that you may or may not agree with depending on the above

That is, surely, the answer to the original question. How you go about using these facts is a personal preference which, most would agree, is fairly unimportant to creative photography... However, there are certain branches of photography where sharpness is the be all and end all.

Each to their own. How about we move on?

You summation is correct in all details. Several previous posts have made similar points without effect. Extraordinary. For my part, I am going back to drinking beer and eating popcorn while watching hockey.

---------- Post added 04-16-2016 at 05:18 PM ----------

light rays are radiation, do you think that has any depth? how many light rays can i hold in a tablespoon?

now give us an example of a physical plane that has no depth.



focus manifests itself as a gradient of sharpness, reducing with distance on either side of the theoretically perfect plane of focus.

and dof exists along the same plane that focus does.

I would like to congratulate you on being the first to introduce the concept of a plane with depth to science. The depth of your understanding of the topic can best be described as a profoundly deep plane.

TTFN

[osv]

I would like to congratulate you on being the first to introduce the concept of a plane with depth to science. The depth of your understanding of the topic can best be described as a profoundly deep plane.

and i'd like to congradulate you on your failed attempt to compare a theoretical but totally non-existent geometrical construct with the real world of photography, were we can see and measure the effects of light and focus planes.

i'd say that deserves another beer, but i think that you've had enough already have a good evening!

[John Poirier]

and i'd like to congradulate you on your failed attempt to compare a theoretical but totally non-existent geometrical construct with the real world of photography, were we can see and measure the effects of light and focus planes.

i'd say that deserves another beer, but i think that you've had enough already have a good evening!

Wow.

I do have some slight acquaintance with the real world of photography, having spent 20 years designing and implementing major technical imaging projects- both film and digital. Nothing compared to your skills, of course.

In my debauched lifestyle one can of beer is plenty, thank you.

Cheers!

---

Last edited by John Poirier; 04-16-2016 at 06:56 PM.

[reh321]

no, sharpness in a photo means the plane of focus, and that might be measured in inches if you are lucky, see the point on the blue line, everything outside of that point is just different degrees of blur... distance to the focus point doesn't change the plane of focus much, if any.
i already proved all that with pics earlier, but you clearly still don't get it...

Actually, those of us who are truly competent in math and physics get it much better than you seem to. "Plane of focus" means only the locus of points which are exactly and precisely in focus - if you would expand your graph in the vertical dimension enough, you would see that the "plane of focus" is essentially one molecule thick, and so that term is largely useless in this type of conversation. The correct term is DOF, namely the area which a viewer will consider to be in focus. That is what we have been talking about, because that is what the OP asked about. You seem to be insisting on a much tighter definition than is usual; the usual definitions are based on what a viewer perceives when looking at the photo as a whole, not looking at one tiny area with a magnifying device. You, of course, may do that if you want to, but the definition you seem to be using now is not consistent with the calculators that even you seemed to accept in the first six pages of this discussion.

Say "f/8 and be there" to anyone with working competence with the 35mm format and the intent of the saying is readily obvious and understood. After all, intelligent leveraging of DOF is chapter two in most introductory photography books.

I covered that already in an earlier post, including the math, it's not relevant to setting the correct focus point.

You are correct that aperture setting has no bearing on setting the "focus point", and that is precisely why your continued insistence on talking about "focus point" and "focus plane" is totally irrelevant to this discussion. The OP asked about how the DOF is determined; the answer is that DOF is determined by the aperture, and there are various means for evaluating the DOF for each aperture setting.

[pacerr]

"Plane of focus" means . . .

Just to throw a little spaghetti sauce at the picture, don't ignore the 'DOF' associated with sharp focus behind the lens at the sensor too.

Except for lenses especially designed for 'flat field' imaging the 'plane' of sharpest focus isn't actually flat, it's curved - typically the surface of spheres who's radii are measured from the lens' optical convergent point to the points of sharpest focus both in front of, and behind, the lens. Considering that one radius may equal anything from MFD to infinity and the other is measured in micrometers . . . hmmm.

We talk about OOF effects in front of the lens in terms of aesthetics but call that which occurs behind the lens undesirable aberrations or dress it up and call it 'bokeh'.

Is a little corner softness caused by that curved 'plane' of focus somewhat compensated for by inherent DOF a good thing?

[ I'm still trying to get a handle on the limits of acceptable DOF when focused at infinity. Would that be at infinity-squared? -cubed? or infinite-infinity? or . . . ? Come to think of it, I've never actually seen infinity. And is the HFD for infinity at 1/3rd-infinity or . . . ? ]

[osv]

Actually, those of us who are truly competent in math and physics get it much better than you seem to. "Plane of focus" means only the locus of points which are exactly and precisely in focus

what would you know about "plane of focus"? you just told us that everything is in focus, your exact words were: "The point is that I want the entire thing in focus - so I want assurance that both the end near me and the end away from me will be in focus. If I glance down at the lens and see that the the focus I have set "goes to infinity", then I have that assurance."

You are correct that aperture setting has no bearing on setting the "focus point",

of course i'm correct, because unlike you, i know that there is no such thing as maximum sharp focus to infinity, and i don't "glance down at the lens and see that the the focus I have set "goes to infinity"... that's sloppy technique.

and that is precisely why your continued insistence on talking about "focus point" and "focus plane" is totally irrelevant to this discussion. The OP asked about how the DOF is determined;

no, his exact words were: "WHERE IS NAIL FOCUS POINT IN SHARPNESS FIELD. IN THE MIDDLE OF IT, JUST ON BEGINNING OR IN THE END OF IT."

he never said anything about how "dof is determined", he's asking where the focus point is.

[TonyW]

[ I'm still trying to get a handle on the limits of acceptable DOF when focused at infinity. Would that be at infinity-squared? -cubed? or infinite-infinity? or . . . ? Come to think of it, I've never actually seen infinity. And is the HFD for infinity at 1/3rd-infinity or . . . ? ]

FWIW, I only tried to focus at infinity once after reading a photo book. I walked and walked for days so that I could reach infinity and finally take the shot. The problem I found was that for some strange reason I could never get any closer and to reach infinity seemed to take forever so I gave up. So I suspect that the HFD may not be 1/3rd but 1/2 at infinity but have no way to confirm

[reh321]

what would you know about "plane of focus"? you just told us that everything is in focus, your exact words were: "The point is that I want the entire thing in focus - so I want assurance that both the end near me and the end away from me will be in focus. If I glance down at the lens and see that the the focus I have set "goes to infinity", then I have that assurance."

of course i'm correct, because unlike you, i know that there is no such thing as maximum sharp focus to infinity, and i don't "glance down at the lens and see that the the focus I have set "goes to infinity"... that's sloppy technique.

No, most everyone understands "in focus" to be short for "no detectable out of focus". You are the one who is focused on this "plane of focus" {regardless of its actual shape}; that concept is immaterial to me, because my only concern is that everything of interest appear to be in focus. My technique is no different from your technique in intent. You peek and peek and peek to see if you can detect points which are not as sharp as you want. I got the same information from the "obsolete barrel markings" while it was still relevent, in the few seconds before the train arrived.

no, his exact words were: "WHERE IS NAIL FOCUS POINT IN SHARPNESS FIELD. IN THE MIDDLE OF IT, JUST ON BEGINNING OR IN THE END OF IT."
he never said anything about how "dof is determined", he's asking where the focus point is.

If you read the entire question for content {including the title}, the question was where the point of actual focus is with respect to the DOF.

[osv]

No, most everyone understands "in focus" to be short for "no detectable out of focus".

no, his first post wasn't relevant to your definition of sloppy focus with the aperture ring, his exact words were: "WHERE IS NAIL FOCUS POINT IN SHARPNESS FIELD"

there is only one correct answer, and tonyw got it right off the bat: "The sharpest point will be exactly the distance your lens focus set (assuming no front or back focus)."

You are the one who is focused on this "plane of focus" {regardless of its actual shape}; that concept is immaterial to me

agreed, sharp focus is immaterial to you because you don't focus the camera, all you do is throw dof at everything, using inaccurate and untested lens barrel markings.

dof and focusing are not the same thing, pacerr spelled that out pretty clearly, you should go back and read what he wrote.

[reh321]

[ I'm still trying to get a handle on the limits of acceptable DOF when focused at infinity. Would that be at infinity-squared? -cubed? or infinite-infinity? or . . . ? Come to think of it, I've never actually seen infinity. And is the HFD for infinity at 1/3rd-infinity or . . . ? ]

First, we have to understand the meaning of "infinity". Just as most everyone understands "in focus" to mean "no detectable out of focus", "infinity" means "no matter how large a number you choose, this one is larger" {*}. Try playing around with a DOF calculator. For example, if I input parameters for my Super-Takumar 35mm lens set at f/8, focusing at 100' {what they call "subject distance of 100 feet"} gives of a DOF of 20' - infinity, while focusing at 10,000' gives a DOF of 25.1' - infinity, and even focusing at 26' gives a DOF of 12.8' - infinity. Thus, when I use the "obsolete lens markings" and want to include as much of the landscape as possible, I will put "infinity" at the left DOF marker, which has the effect of bringing more of the foreground "into focus" while still giving as much background detail as my system is able to capture.


{*} actually, mathematicians recognize several levels of "infinity", but my blanket definition applies to all of them

[John Poirier]

What is Buzz Lightyear's catchphrase? I think it's "To infinity and beyond!!!"

[reh321]

no, his first post wasn't relevant to your definition of sloppy focus with the aperture ring, his exact words were: "WHERE IS NAIL FOCUS POINT IN SHARPNESS FIELD"

Later posts indicated that DOF-related responses were exactly what was wanted:

Have a look here, that may help
Online Depth of Field Calculator.
Typically 1/3 before and 2/3 behind the focused distance.

thank you, that's pretty helpful

I was just trying to find out, is nail focus begin more in the front, exactly front, or closer to the middle of, what we called acceptable sharpness.
If I nail singer, from 3,4 m away, and he move after focusing 30 cm to me, with his body, will he be in focus if I choose for example f8 or even f11?
Or on the opposite side, If he move away 30 cm from me, after focusing.

Especially note the concerns about the person moving towards or away; your method requires an ability to precisely determine how much the person moved, and then repeat it yourself {which is a real problem in some venues, such as first row in balcony seating}, while having an adequate DOF provides assurance that the person remains in the area of "accepted sharpness" {OP's words}

agreed, sharp focus is immaterial to you because you don't focus the camera, all you do is throw dof at everything, using inaccurate and untested lens barrel markings.

No, I do focus the lens when possible, {I'm not sure what "focusing a camera" would consist of - is this another one of your invented words, like "focus plane"} which is most of the time, but I also suggest keeping a sufficiently wide DOF as added assurance, which {as indicated in the quote directly above} is the concern that started this thread. And you cannot be sure your focus, chimp, repeat pattern works at all if you have no time to prepare {for example, my AFT pictures} or if you have nothing to focus on in advance {basketball players in the air or perhaps cars at IMS where they keep the track clean and smooooth}

dof and focusing are not the same thing, pacerr spelled that out pretty clearly, you should go back and read what he wrote.

Yes, I especially noted the place which pointed out that your "focus plane" isn't:

Except for lenses especially designed for 'flat field' imaging the 'plane' of sharpest focus isn't actually flat, it's curved - typically the surface of spheres who's radii are measured from the lens' optical convergent point to the points of sharpest focus both in front of, and behind, the lens. Considering that one radius may equal anything from MFD to infinity and the other is measured in micrometers . . . hmmm.

[stevebrot]

Each to their own. How about we move on?

One could only wish that the mods close this thread soon.

Steve

[mee]

Geometry lesson for Osv ... a plane has no depth. ☺

The pilot might have just called to say he found one that does..