[stevebrot]

there is no doubt that a sharp plane of focus can be seen...

I could not help captioning your image...

OSV Demonstrates the Thickness of a Plane (metaphorically speaking*)



Extremely cool image, BTW.


Steve

* Geometrically speaking it goes something like this: https://en.wikipedia.org/wiki/Plane_%28geometry%29 with the emphasis being on the words "two-dimensional".

---

Last edited by stevebrot; 04-20-2016 at 03:34 PM.

[emalvick]

And, as much as you guys have been arguing geometry, if you want to get truly technical and accurate, this focal "plane" is a actually part of the surface of a sphere, which is not a plane. I suppose mathematically, it is still 2D, but the 2D that matter are angular with no variation in depth (radius); the reality is that is no longer planar geometry even. The concept of a focal plane as Steve quoted the definition of is a simplification of the real optics of our lenses and their focal points. People struggle with math and geometry, in general, so forcing the geometry and trigonometry associated with a sphere is way more complicated than the approximately correct planar approximation being debated in this thread.

Thus, it has always driven me crazy when people use wide angled lenses, such as a 15 mm lens and complain that the edges are soft. They shoot a brick wall and show the soft lines at the edges or corners. Well, the reality is that the points of focus are spherical; the flat brick wall is going to be much further away from the camera at its extremes and out of that focal "plane" and by observation out of the zone that would represent the depth of field.

And for those that want to argue that the DOF represents some plane, it would be more appropriate to argue that the DOF represents the distance between two planes. The two planes being the ones that one could argue separate the area that acceptably in focus from the out of focus areas in front of or behind that area. Of course the location of those planes is again dependent on what the word acceptable means to the individual. Heck, if I take my glasses off, I question whether that acceptable area even exists.

[MarkJerling]

Precisely!

[stevebrot]

this focal "plane" is a actually part of the surface of a sphere

Focal plane is a true plane (abstract concept). What are not planar are the Focus Plane and Plane of Focus. Those are determined by the lens design and are often (usually? almost always?) curved*, but still have the thickness of a point. And a point, after all, is defined in zero dimensions and has no measurable attributes outside of location and then only when considered from the perspective of a higher dimension.

And for those that want to argue that the DOF represents some plane, it would be more appropriate to argue that the DOF represents the distance between two planes. The two planes being the ones that one could argue separate the area that acceptably in focus from the out of focus areas in front of or behind that area.

Yep...Of course, though I only say that because I am hampered by obsolete tech.

Steve

* Yes, even when we are using a "Planar" lens design. Wishful thinking on the part of those people at Zeiss.

---

Last edited by stevebrot; 04-20-2016 at 04:18 PM.

[pacerr]

Ya sure we don't need to throw 'crop factor' in here too? (D an' R)

[osv]

And for those that want to argue that the DOF represents some plane, it would be more appropriate to argue that the DOF represents the distance between two planes. The two planes being the ones that one could argue separate the area that acceptably in focus from the out of focus areas in front of or behind that area. Of course the location of those planes is again dependent on what the word acceptable means to the individual. Heck, if I take my glasses off, I question whether that acceptable area even exists.

defining it as being two delineated planes is essentially the same argument that i posed earlier, when i said that perfect focus can be measured; i posted a 100% crop pic to back that up.

it works at any level because we can't visually differentiate graduated blur beyond a certain point, and i defined that to be measured at 100% size, because blowing the pic up to 200% isn't going to make it sharper in that area... so there is a realistic hard limit to this, where distance-influenced perception is not a factor, and that's where i shoot.

---------- Post added 04-20-16 at 07:56 PM ----------

I could not help captioning your image...

OSV Demonstrates the Thickness of a Plane (metaphorically speaking*)

Extremely cool image, BTW.

and thx, i like that pic a lot, if you only knew what i went through to get that shot.

[reh321]

And for those that want to argue that the DOF represents some plane, it would be more appropriate to argue that the DOF represents the distance between two planes. The two planes being the ones that one could argue separate the area that acceptably in focus from the out of focus areas in front of or behind that area. Of course the location of those planes is again dependent on what the word acceptable means to the individual. Heck, if I take my glasses off, I question whether that acceptable area even exists.

defining it as being two delineated planes is essentially the same argument that i posed earlier, when i said that perfect focus can be measured; i posted a 100% crop pic to back that up.

These are different things; emalvick is talking about DOF {which is "acceptable focus" - basically what we see when viewing the image from a distance which allows us to see the whole thing at once} and you're talking about "perfect focus".

Part of the issue here is technology. If I were to post a scan of a slide I took in 1992, you would rightfully comment on its "lack of sharpness". I had an eye-opening experience when I mounted the Pentax-A 50mm f/1.7 kit-lens {kitted with the Super Program I bought in 1984} on my K-30; the pictures were much sharper than I was getting when I retired that camera + lens in 1995. The difference was not 20 years of rest for the lens; the difference is that the K-30 provides much more sharpness than Kodachrome 25 ever did. The same thing is true of today's equipment; no matter how wonderful it may seem today, it provides only a hint of what is actually out there; that is, true "perfect focus" exists physically only at the molecules located on the plane of focus, but current equipment shows a noticeable difference only when you get some distance away from there. That distance is embedded in our definition of DOF. I don't expect to be around 30 years from now, but I expect that this kind of progress will continue, and the difference between equipment available in 2046 and what we have today could be just as dramatic as the difference between today and 1986. In 2046 any grandchildren {or great grandchildren} in my line might laugh at our best efforts today, and most likely that equipment will show differences {at the pixel-peeking level} earlier as they get away from the plane of focus, but regardless of when those differences show, the simple scientific fact is that the plane of focus is the only place with "perfect focus", regardless of when the differences show up using our equipment.

---

Last edited by reh321; 04-21-2016 at 07:53 AM. Reason: arithmetic mistake in originally figuring age of "A" lens

[osv]

These are different things; emalvick is talking about DOF {which is "acceptable focus" - basically what we see when viewing the image from a distance which allows us to see the whole thing at once} and you're talking about "perfect focus".

no, that's not even logical, because the definition of dof has no distance limitations associated with it, dof doesn't suddenly stop existing just because you are at 100%... if for example you zoom in to 100% and crop the shot there, that's "the whole thing at once".

it doesn't matter what equipment you use, failing to set accurate focus will result in slop.

[reh321]

no, that's not even logical, because the definition of dof has no distance limitations associated with it, dof doesn't suddenly stop existing just because you are at 100%... if for example you zoom in to 100% and crop the shot there, that's "the whole thing at once".

There you go again, quibling over details and going totally off topic. So, just for you, I will restate my post:

And for those that want to argue that the DOF represents some plane, it would be more appropriate to argue that the DOF represents the distance between two planes. The two planes being the ones that one could argue separate the area that acceptably in focus from the out of focus areas in front of or behind that area. Of course the location of those planes is again dependent on what the word acceptable means to the individual. Heck, if I take my glasses off, I question whether that acceptable area even exists.

defining it as being two delineated planes is essentially the same argument that i posed earlier, when i said that perfect focus can be measured; i posted a 100% crop pic to back that up.

The statement by emalvick is about DOF, and saying it can be viewed as the region between two planes. "Perfect focus" can be truly achieved at the plane of the focus only. Talking about the region between two planes {emalvick} is not the same as talking about one plane {osv}. Not the same issue, not the same discussion.

it doesn't matter what equipment you use, failing to set accurate focus will result in slop.

Everyone agrees that the more accurate the focus, the better the image.

[osv]

There you go again, quibling over details and going totally off topic. So, just for you, I will restate my post:
The statement by emalvick is about DOF, and saying it can be viewed as the region between two planes. "Perfect focus" can be truly achieved at the plane of the focus only.

no, the theoretical perfect plane of focus is not visible, it can't be seen with the human eye, so perfect focus = dof, it's all just graduated degrees of blur.

once you eliminate the distance perception factor, by going to 100%, plane of focus is defined by the limits of eyesight, the viewing medium, and the resolution of the gear, per the 100% pic i posted.

Everyone agrees that the more accurate the focus, the better the image.

no, you think that dof will cover up your inability to focus the camera correctly, you've stated that repeatedly in this thread, it's a fail.

you can't focus a camera with the aperture ring.

[mohb]

no, you think that dof will cover up your inability to focus the camera correctly, you've stated that repeatedly in this thread, it's a fail.

you can't focus a camera with the aperture ring.

osv, do you only use a camera on a monumentally solid tripod and make all adjustments remotely? If not then surely you cannot claim to be getting 'perfect focus'

[reh321]

no, the theoretical perfect plane of focus is not visible, it can't be seen with the human eye, so perfect focus = dof, it's all just graduated degrees of blur.
once you eliminate the distance perception factor, by going to 100%, plane of focus is defined by the limits of eyesight, the viewing medium, and the resolution of the gear, per the 100% pic i posted.

Wrong again. My point was just that - perfect focus is a plane {two dimensional}. You, yourself, made that very point several times, including just yesterday

"A camera lens can only focus on one plane of the subject. This is the only area of the scene that is really sharp." Depth-of-field - Canon Professional Network

You cannot see longitude lines {one dimensional} either, but we can locate them and we can use them for reference. That plane of focus reference is used in determining the DOF that we actually work within.

no, you think that dof will cover up your inability to focus the camera correctly, you've stated that repeatedly in this thread, it's a fail.
you can't focus a camera with the aperture ring.

Misrepresentation again. What I have said repeatedly is that a comfortable DOF provides a greater region of acceptable focus. The aperture ring provides that at the cost of having to go with higher ISO or lower shutter speed, the tradeoff that we've all been working with for many years. Some people use DOF to help tell their story - to include or exclude areas, while others, like the OP, may want to expand the area in case they do not have time to respond to changing circumstances. You, yourself, talk about taking a step forward if the car moves over in the track. Everyone needs options; it is great for you to be able to step forward at those venues, but sometimes people are in a position where they cannot change position in a timely fashion {again, my example that you probably would limit your forward movement if you were in the very front row of the balcony or right at the barrier at IMS}.

[emalvick]

Perfect focus does not equal acceptable focus... What I see when you say DOF = Perfect focus is that you have a loose definition of perfect.

In terms of physics and optics, there is only one plane where focus can truly be perfect. That's a fact. But, no camera is perfect, and neither are eyes. So of course we calibrate ourselves to accept a range of focus as "perfect" and this range should have some depth. After all, it isn't like one molecule off perfect means a blurry mess. But, you do have to realize that when it comes to depth of field, most people are not going to consider points at the the extremes of the traditional depth of field as perfect focus, just acceptable. And, of course the definition and formulas for defining depth of field are somewhat arbitrary based on mathematics and the expected level of softness people will accept as "in focus" . And this as become the standard for markings on our lenses and most apps and equations and so forth. All I see that makes you different is that you don't find what has been called acceptable as acceptable for you, which is fine. You essentially define depth of field as an area that you consider as "perfect" focus, which in terms of real physics is just your limit on what is acceptable.

All this thread has proven is that the acceptable depth of field is quite subjective and despite physical aspects such as aperture, focal distance, viewing distance, viewing size, etc., there is still a level of opinion to what you and or the next person might consider acceptable. It's all just opinions, and respectful people recognize that everyone might have a different one, and that your own opinion isn't necessarily better than anyone else's.

[clackers]

no, the theoretical perfect plane of focus is not visible, it can't be seen with the human eye.

He can't see points in focus?

Extraordinary statement from someone who claims to use manual focus.

[osv]

osv, do you only use a camera on a monumentally solid tripod and make all adjustments remotely? If not then surely you cannot claim to be getting 'perfect focus'

what shutter speeds did i use to take the sharp pics that i've posted?

do you really think that all shutter speeds need "a monumentally solid tripod" and remote control over the camera?

---------- Post added 04-21-16 at 02:09 PM ----------

Wrong again. My point was just that - perfect focus is a plane {two dimensional}.

wrong, you contradicted yourself once again, as usual: "A camera lens can only focus on one plane of the subject. This is the only area of the scene that is really sharp." Depth-of-field - Canon Professional Network

canon specifically defines a plane of focus as being visible, because they said it's sharp... a theoretical perfect plane of focus is not visible, so it's irrelevant to the discussion, stop posting non-existent failed geometrical constructs.

the 100% crop i posted is exactly what canon says a plane of sharp focus is.

What I have said repeatedly is that a comfortable DOF provides a greater region of acceptable focus.

no, what you keep telling people to do is use dof in place of focusing, which is a fail.