# How Useful is Merklinger's "Object Field" Focusing ?

Started Jul 24, 2013 | Discussions
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How Useful is Merklinger's "Object Field" Focusing ?

Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?

When focusing at "infinity", the Near Focus Distance moves from being equal to the Hyperfocal Distance divided by 2 (as is the case when focusing at the Hyperfocal Distance) to being equal to the Hyperfocal Distance itself (Equation 69, Page 17 of Jeff Conrad's Depth of Field in Depth):

http://www.largeformatphotography.info/articles/DoFinDepth.pdf

The writings of Harold Merklinger describe his related "Object Field" techniques (A Different Approach - The Object Field, Chapter 5, Pages 25-38, The INs and OUTs of FOCUS) here:

http://www.trenholm.org/hmmerk/TIAOOFe.pdf

... and in a shorter, abbreviated version (from a reprinted "Shutterbug" magazine article) here:

http://www.trenholm.org/hmmerk/DOFR.html

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

Translated back to the film/sensor plane, the above parameters are used to define a given Circle of Confusion diameter. However, Merklinger's Object Field approach appears to concentrate exclusively on the Object Space side of the camera lens with his "Disk of Confusion" mathematical identities.

What I am wondering is this:

The "price paid" for focusing at "infinity" (as opposed to focusing at some Hyperfocal Distance derived from some given Circle of Confusion diameter) seems to be that the Near Focus Distance (of a "depth of field of acceptable focus") from the camera is doubled in value as a result. Depending upon the intended nature of the composition as it relates to the subject-matter desired to be in "acceptable" focus, this may (or may not) represent a significant sacrifice.

If the viewer of a printed/displayed image may (as a result of individual visual acuity, viewing-size, and viewing distance) be unable to perceive (some or all of) the increased resolution of the image's far-field subject-matter, then would Merklinger's "Object Field" focusing technique represent a net improvement - or are (some or all of) the alleged advantages of the technique (relating to the resolution of far-field subject-matter) diminished or negated as a result ?

DM ...

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Establishing acceptable object detail?

Detail Man wrote:

Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?

No opinion on that. It seems more like a consequence of Merklinger's method than a goal of the method.

Since the method only controls detail resolution in front of the plane in focus (at least in the "For dummies" version of his method that I am familiar with), you have to make sure that you have nothing important behind the plane of focus.

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

No, as I have understood it, it concentrates on which size of details in the foreground of the scene you want to be able to resolve.

While I can sympathize with the reasoning behind this approach, I have one huge problem with it:

When I compose a scene, I have great difficulty imagining how small details in the foreground of the scene I need to be able to resolve to get a photo which appears sharp.

But I guess that this adds nothing new to what you have already said.

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Re: Establishing acceptable object detail?

Allan Olesen wrote:

Detail Man wrote:

Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?

No opinion on that. It seems more like a consequence of Merklinger's method than a goal of the method.

Since the method only controls detail resolution in front of the plane in focus (at least in the "For dummies" version of his method that I am familiar with), you have to make sure that you have nothing important behind the plane of focus.

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

No, as I have understood it, it concentrates on which size of details in the foreground of the scene you want to be able to resolve.

While I can sympathize with the reasoning behind this approach, I have one huge problem with it:

When I compose a scene, I have great difficulty imagining how small details in the foreground of the scene I need to be able to resolve to get a photo which appears sharp.

But I guess that this adds nothing new to what you have already said.

Think that 'simple' things like focusing and determining how deep the DoF is can be surprisingly difficult in practice. Which CoC should I use if I want to know how deep the Dof is when viewing an image at 100%? Should CoC in that case be something like 2x the linear pixel size, or maybe even less? (meaning that I'll get much less Dof than dofmaster.com says, if using the standard CoC value for the sensor size).

And how do I focus at e.g. 6 meter if that is what I (for whatever reason) have decided I want to do? Is PDAF accurate enough? (dont think so, especially not with WA/UWA lenses) Can I trust the focus scale on the lens? And what about field curvature, and maybe also focus shift when stopping down? All in all I think that getting the correct/preferred focus (and DoF) can be a bit of a challenge.

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Re: How Useful is Merklinger's "Object Field" Focusing ?

Detail Man wrote:

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

I find precisely that to be one of the benefits of Merklinger's approach. It does not assume a particular display size or viewing condition. I cannot see any advantage of such an assumption unless you know you will be constrained to those particular circumstances which, I believe, is a rather arbitrary choice.

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Re: How Useful is Merklinger's "Object Field" Focusing ?

Detail Man wrote:

Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?

Well if the subject is at infinity, then focusing at infinity will make the subject as in-focus as possible. If you focus at hyperfocal distance, then the subject at infinity is going to be about as out-of-focus as it is possible to be while still being "acceptable."

As you discuss later, it's harder to say whether the result would be "better," since you'd be losing something on a nearby subject which you (presumably) also find important to your picture.

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

He follows the traditional definition that "resolving" details at some size means you can tell them apart. If the CoCs of neighboring points are big enough that they overlap, then you aren't going to be able to tell them apart very well. Visual acuity plays into this only a little.

Translated back to the film/sensor plane, the above parameters are used to define a given Circle of Confusion diameter. However, Merklinger's Object Field approach appears to concentrate exclusively on the Object Space side of the camera lens with his "Disk of Confusion" mathematical identities.

I think it's an interesting way of looking at DOF. The usual method concentrates (I'll avoid "focuses" ) on minimizing the size of circles on the surface of the end print (or however else you look at your photos). Merklinger's method gets you to think about which objects in the actual three-dimensional scene will be "resolved."

What I am wondering is this:

...

If the viewer of a printed/displayed image may (as a result of individual visual acuity, viewing-size, and viewing distance) be unable to perceive (some or all of) the increased resolution of the image's far-field subject-matter, then would Merklinger's "Object Field" focusing technique represent a net improvement - or are (some or all of) the alleged advantages of the technique (relating to the resolution of far-field subject-matter) diminished or negated as a result ?

If two objects aren't "resolved" in the technical sense, then they will never be resolved, no matter how good your eyes are or how much you enlarge the image.

If your print size happens to be small enough that you couldn't see those objects anyway, then sure, it doesn't help.  (But that also applies to the usual method of DOF, right? I mean, nothing has to be very well focused if your print is small enough...  )

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Re: Establishing acceptable object detail?

Allan Olesen wrote:

When I compose a scene, I have great difficulty imagining how small details in the foreground of the scene I need to be able to resolve to get a photo which appears sharp.

That's the bit that I find easy. If you have a bit of an idea for dimension you can look at something and estimate the size of the details that you want to be rendered. For instance, grass blades are a couple of millimetres wide, veins on a leaf about half a millimetre, as is the texture on bricks and rocks. Then you size the aperture according to that estimate. The 'Dummies' method says just make the aperture the size of the minimum feature, the more sophisticated says scale it according to its position between the aperture and the plane of focus, so if its half the distance make the aperture twice the size, and so on. So the trick is to visualise in terms of the scene you see in front of you, not the scene that you imagine in the final image.

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Bob

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Re: Establishing acceptable object detail?

Bobn2 wrote:

Allan Olesen wrote:

When I compose a scene, I have great difficulty imagining how small details in the foreground of the scene I need to be able to resolve to get a photo which appears sharp.

That's the bit that I find easy. If you have a bit of an idea for dimension you can look at something and estimate the size of the details that you want to be rendered. For instance, grass blades are a couple of millimetres wide, veins on a leaf about half a millimetre, as is the texture on bricks and rocks. Then you size the aperture according to that estimate.

Well, that is the easy part. The hard part is "Would my sensor even be able to resolve the veins on this leaf, even if my focusing method allows it."

And yes, I know that usual DOF calculations doesn't really answer that question either since the usual CoC is so much larger than the detail the sensor can resolve. But at least there is a rather constant relationship between the two as long as you keep using the same camera.

the more sophisticated says scale it according to its position between the aperture and the plane of focus,

Yes, I already figured that out, even though it wasn't mentioned in the Dummies method.

I think that for me, the Merklinger method is a good tool for understanding DoF mechanics, but not for actually composing a scene.

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Re: Establishing acceptable object detail?

Allan Olesen wrote:

Bobn2 wrote:

Allan Olesen wrote:

When I compose a scene, I have great difficulty imagining how small details in the foreground of the scene I need to be able to resolve to get a photo which appears sharp.

That's the bit that I find easy. If you have a bit of an idea for dimension you can look at something and estimate the size of the details that you want to be rendered. For instance, grass blades are a couple of millimetres wide, veins on a leaf about half a millimetre, as is the texture on bricks and rocks. Then you size the aperture according to that estimate.

Well, that is the easy part. The hard part is "Would my sensor even be able to resolve the veins on this leaf, even if my focusing method allows it."

That bit, I leave to the sensor - after all, hyperfocal technique doesn't tell you whether the sensor's going to image the full splendour of your in-focus area.

And yes, I know that usual DOF calculations doesn't really answer that question either since the usual CoC is so much larger than the detail the sensor can resolve. But at least there is a rather constant relationship between the two as long as you keep using the same camera.

But that is only if you use the same CoC regardless of how you intend to use the image.

the more sophisticated says scale it according to its position between the aperture and the plane of focus,

Yes, I already figured that out, even though it wasn't mentioned in the Dummies method.

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Bob

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Re: Establishing acceptable object detail?

Bobn2 wrote:

And yes, I know that usual DOF calculations doesn't really answer that question either since the usual CoC is so much larger than the detail the sensor can resolve. But at least there is a rather constant relationship between the two as long as you keep using the same camera.

But that is only if you use the same CoC regardless of how you intend to use the image.

Yes, I know.

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Re: Establishing acceptable object detail ?

Allan Olesen wrote:

Detail Man wrote:

Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?

No opinion on that. It seems more like a consequence of Merklinger's method than a goal of the method.

Since the method only controls detail resolution in front of the plane in focus (at least in the "For dummies" version of his method that I am familiar with), you have to make sure that you have nothing important behind the plane of focus.

(With the "Object Field" system), the Plane of Focus exists at the arithmetic center of what would be considered the "Near" and "Far" Focus Distances (derived below):

Dn = (D) x ( 1 - ( (S) (F) / (L) ) )

Df = (D) x ( 1 + ( (S) (F) / (L) ) )

where:

Dn is the Near Focus Distance;
Df is the Far Focus Distance;
D is the Camera to Subject Distance (from lens front nodal-plane to plane-of-focus);
S is the object-field Spot Size as specified by photographer (the "Disk of Confusion");
F is the F-Number;
L is the actual Focal Length.

Calculating the difference between Df and Dn (above) yields a quantity similar to Depth of Field:

(Df - Dn) = (2) x (D) x (S) x (F) / (L)

On the other hand, (with the "Depth of Field" system), the Plane of Focus exists at the geometric center of the "Near" and "Far" Focus Distances. Thus, the (image-side) COC (as geometrically projected into Object Space) continues to grow in size behind the Plane of Focus.

Regarding subject-matter that is "important behind the plane of focus":

Cases have been made by proponents of Merklinger's "Object Field" focusing method that the fact that the (projected into Object Space, effective) COC diameter (when using "Hyperfocal Focusing") continues to grow in size behind the Plane of Focus - and in amounts which end up being larger than Merklinger's Object Space "Disk of Confusion". This seems to have some merit.

On the other hand, it seems that the relative amount that such (behind the Plane of Focus) subject-matter respresents within the recorded image-frame is (also) decreasing (in inverse proportion to the distance between the camera and that far-field subject-matter) - such that the increasing size of the effective COC diameter projected into Object Space (in some particular proportion to the distance between the Plane of Focus and that far-field subject-matter) would seem to become less of an issue when considering it on an "image level" basis. This also seems to have some merit.

Am here assuming that the size of the COC derived from measures of (20/20) human visual acuity at given viewing-sizes and viewing distances referred to the film/sensor plane (such as the 30 Microns in the case of Full Frame format commonly cited for a 10" viewing-size from a viewing-distance of 25 cm) is larger than the size of a (de-mosaiced) pixel (which, depending on the particular de-mosaicing algorithm utilized) takes into account at least 2x2 photosite arrays. Thus, I am assuming that (de-mosaiced) "pixel-ization" is not a complicating factor in this particular analysis.

Thus, as both arguments described above seem to each have some merit (when considered on an individual basis), I am hoping to define the parameters surrounding under what specific conditions one or the other of these contrary viewpoints should be taken, and applied in practice.

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

No, as I have understood it, it concentrates on which size of details in the foreground of the scene you want to be able to resolve.

While I can sympathize with the reasoning behind this approach, I have one huge problem with it:

When I compose a scene, I have great difficulty imagining how small details in the foreground of the scene I need to be able to resolve to get a photo which appears sharp.

I agree on that point. Not only is the idea of wondering and guessing what the minimum physical dimensions of interest to be resolved in object-space within a plethora of varied and intricate foliage existing in front of (as well as behind) the plane of focus a non-trivial and unexact proposition, ... in order to malke such musings more than a worst-case (that is, at the position of the camera), one has to (as well) scale those estimates of physical size by a scalar that varies linearly between the position of the camera and the plane of focus.

Rough approximations may be fine for those for whom resolution of intricate folliage detail represents a non-critical aside, but such mental acrobatics are a "non starter" for my applications.

But I guess that this adds nothing new to what you have already said.

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Re: Establishing acceptable object detail ?

Detail Man wrote:

Regarding subject-matter that is "important behind the plane of focus":

Cases have been made by proponents of Merklinger's "Object Field" focusing method that the fact that the (projected into Object Space, effective) COC diameter (when using "Hyperfocal Focusing") continues to grow in size behind the Plane of Focus - and in amounts which end up being larger than Merklinger's Object Space "Disk of Confusion". This seems to have some merit.

I don't understand this reasoning. Merklinger's Object Space "Disk of Confusion" will continue to grow too. At a distance of 2x the distance to the focus plane it will have a diameter of F/L (the chosen min. resolvable detail according to the "For Dummies" Merklinger method). Behind that point it will continue to grow beyond the chosen min. resolvable detail.

But the growth is more unpredictable with the Merklinger method, which was the point I was trying to make. When you use the Merklinger method, it is not simple to estimate how much the moon will be out of focus - unless the moon is what you have chosen to focus on.

On the other hand, it seems that the relative amount that such (behind the Plane of Focus) subject-matter respresents within the recorded image-frame is (also) decreasing (in inverse proportion to the distance between the camera and that far-field subject-matter) - such that the increasing size of the effective COC diameter projected into Object Space (in some particular proportion to the distance between the Plane of Focus and that far-field subject-matter) would seem to become less of an issue when considering it on an "image level" basis. This also seems to have some merit.

Well, that is the natural consequence of using a DoF criteria which is based on dimensions in the photo instead of dimensions in world in front of the camera. And that is what makes it predictable how much the moon will be out of focus.

Thus, as both arguments described above seem to each have some merit (when considered on an individual basis), I am hoping to define the parameters surrounding under what specific conditions one or the other of these contrary viewpoints should be taken, and applied in practice.

That is out of my league.

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Correction: Establishing acceptable object detail ?

Detail Man wrote:

(With the "Object Field" system), the Plane of Focus exists at the arithmetic center of what would be considered the "Near" and "Far" Focus Distances (derived below):

Dn = (D) x ( 1 - ( (S) (F) / (L) ) )

Df = (D) x ( 1 + ( (S) (F) / (L) ) )

where:

Dn is the Near Focus Distance;
Df is the Far Focus Distance;
D is the Camera to Subject Distance (from lens front nodal-plane to plane-of-focus);
S is the object-field Spot Size as specified by photographer (the "Disk of Confusion");
F is the F-Number;
L is the actual Focal Length.

Calculating the difference between Df and Dn (above) yields a quantity similar to Depth of Field:

(Df - Dn) = (2) x (D) x (S) x (F) / (L)

On the other hand, (with the "Depth of Field" system), the Plane of Focus exists at the geometric center of the "Near" and "Far" Focus Distances. Thus, the (image-side) COC (as geometrically projected into Object Space) continues to grow in size behind the Plane of Focus.

On the other hand, (with the "Depth of Field" system), the Plane of Focus exists at the harmoninc mean of the "Near" and "Far" Focus Distances. Thus, the (image-side) COC (as it exists when projected into Object Space) continues to grow in size behind the Plane of Focus.

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Re: Establishing acceptable object detail ?

Allan Olesen wrote:

When you use the Merklinger method, it is not simple to estimate how much the moon will be out of focus - unless the moon is what you have chosen to focus on.

This does seem like a limitation of Merklinger's method. It only works for sizes and distances that you are familiar with. The size and distances of some leaves might be something you can guess at. The moon on the other hand is a huge size at an astronomical distance. Maybe hyperfocal distances are worth keeping around after all (although... maybe you don't want to put the moon right at the limit of your DOF).

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Re: Establishing acceptable object detail ?

Allan Olesen wrote:

Detail Man wrote:

Regarding subject-matter that is "important behind the plane of focus":

Cases have been made by proponents of Merklinger's "Object Field" focusing method that the fact that the (projected into Object Space, effective) COC diameter (when using "Hyperfocal Focusing") continues to grow in size behind the Plane of Focus - and in amounts which end up being larger than Merklinger's Object Space "Disk of Confusion". This seems to have some merit.

I don't understand this reasoning. Merklinger's Object Space "Disk of Confusion" will continue to grow too. At a distance of 2x the distance to the focus plane it will have a diameter of F/L (the chosen min. resolvable detail according to the "For Dummies" Merklinger method). Behind that point it will continue to grow beyond the chosen min. resolvable detail.

I think that in both cases the ratio of the Object Space "spot-sizes" (R, below) are defined by:

R = ( Df / D - 1 ) / ( 1 - Dn / D )

where:

D is the Camera to Subject Distance (front-nodal-plane to plane-of-focus distance);

Dn is the Near Focus Distance (with a numerical value that is always less than D);

Df is the Far Focus Distance (with a numerical value that is between D and infinity).

So, for any focusing scheme that attempts to resolve subject-matter existing behind the Plane of Focus, the size of the (Object Space) "Disk of Confusion" continues to grow without bounds.

But the growth is more unpredictable with the Merklinger method, which was the point I was trying to make. When you use the Merklinger method, it is not simple to estimate how much the moon will be out of focus - unless the moon is what you have chosen to focus on.

Would not it be true that if the Plane of Focus chosen when using "Object Field" focusing exists at any distance farther away from the camera than the "Hyperfocal Distance" (but closer than the moon itself), then as a result the moon would invariably seem to be in better focus than had the "Hyperfocal Distance" been chosen instead ? If so, why would such mysteries be vexing ?

On the other hand, it seems that the relative amount that such (behind the Plane of Focus) subject-matter respresents within the recorded image-frame is (also) decreasing (in inverse proportion to the distance between the camera and that far-field subject-matter) - such that the increasing size of the effective COC diameter projected into Object Space (in some particular proportion to the distance between the Plane of Focus and that far-field subject-matter) would seem to become less of an issue when considering it on an "image level" basis. This also seems to have some merit.

Well, that is the natural consequence of using a DoF criteria which is based on dimensions in the photo instead of dimensions in world in front of the camera. And that is what makes it predictable how much the moon will be out of focus.

Thus, as both arguments described above seem to each have some merit (when considered on an individual basis), I am hoping to define the parameters surrounding under what specific conditions one or the other of these contrary viewpoints should be taken, and applied in practice.

That is out of my league.

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Re: Establishing acceptable object detail ?

Detail Man wrote:

I think that in both cases the ratio of the Object Space "spot-sizes" (R, below) are defined by:

R = ( Df / D - 1 ) / ( 1 - Dn / D )

where:

D is the Camera to Subject Distance (front-nodal-plane to plane-of-focus distance);

Dn is the Near Focus Distance (with a numerical value that is always less than D);

Df is the Far Focus Distance (with a numerical value that is between D and infinity).

So, for any focusing scheme that attempts to resolve subject-matter existing behind the Plane of Focus, the size of the (Object Space) "Disk of Confusion" continues to grow without bounds.

Yes, that was my reasoning, though I was referring to the actual Object Space "spot-sizes", not the ratio between two of them.

At a given distance A from the camera, where A > D, the object space spot size S will be:

S = (A/D - 1) * L / F

Where D, L and F follows your definitions from a previous post.

But the growth is more unpredictable with the Merklinger method, which was the point I was trying to make. When you use the Merklinger method, it is not simple to estimate how much the moon will be out of focus - unless the moon is what you have chosen to focus on.

Would not it be true that if the Plane of Focus chosen when using "Object Field" focusing exists at any distance farther away from the camera than the "Hyperfocal Distance" (but closer than the moon itself), then as a result the moon would invariably seem to be in better focus than had the "Hyperfocal Distance" been chosen instead ? If so, why would such mysteries be vexing ?

It would only be true at the same aperture setting. And since the two methods can lead to different aperture settings, I do not agree.

So, in order to know if you are focusing behind the hyperfocal distance at the aperture you chose with the Merklinger method, you would need to calculate this hyperfocal distance anyway. And consequently, you haven't made your life simpler - though simplicity is one of the sales points for the Merklinger method.

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Re: How Useful is Merklinger's "Object Field" Focusing ?

Detail Man wrote:

Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?

Absolutely, without a doubt.

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

Well, you could argue that it doesn't need to because it maximises the possible sharpness where it matters.

What I am wondering is this:

The "price paid" for focusing at "infinity" (as opposed to focusing at some Hyperfocal Distance derived from some given Circle of Confusion diameter) seems to be that the Near Focus Distance (of a "depth of field of acceptable focus") from the camera is doubled in value as a result. Depending upon the intended nature of the composition as it relates to the subject-matter desired to be in "acceptable" focus, this may (or may not) represent a significant sacrifice.

AFAIK, Merklinger only advocates focussing at infinity in very specific circumstances, it's not his method as such, so you may be wondering about something different. (It's a good exercise for the reader to find out when he said to focus at infinity and why.)

If the viewer of a printed/displayed image may (as a result of individual visual acuity, viewing-size, and viewing distance) be unable to perceive (some or all of) the increased resolution of the image's far-field subject-matter, then would Merklinger's "Object Field" focusing technique represent a net improvement - or are (some or all of) the alleged advantages of the technique (relating to the resolution of far-field subject-matter) diminished or negated as a result ?

Depends on what you mean by his "technique" - focus at infinity, or focus on the furthest thing that you want to be truely sharp in the image?

My guess is, if the viewer can't see well enough to differentiate levels of sharpness/focus/resolution in the image, it doesn't matter whether you went hyperfocal or beyond. IOW, if the alleged advantages of focussing on the furthest thing you want to be sharp are negated, then so are the alleged (and far more dubious) advantages of focussing at the hyperfocal distance.

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Re: How Useful is Merklinger's "Object Field" Focusing ?

If I read him [in the short paper] correctly, he means the latter.

WilbaW wrote:

Depends on what you mean by his "technique" - focus at infinity, or focus on the furthest thing that you want to be truely sharp in the image?

BTW: I don't know where this thread was originally, but I'm a bit a bit curious why this was moved here. This is actually a subject that better fits in a 'photography praxis' forum. Maybe the 'general photo techniques' is intended as such?

(not that I mind, this is forum I visiit, the other so far not)

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Re: How Useful is Merklinger's "Object Field" Focusing?

As a layman photographer my contribution (for what it's worth) is not scientific at all.  What I got when I read Merklinger's article can be summed up as:  Focus the camera on what you want the viewer to focus on.  If I want something in the background to be sharp then clearly I will be focusing on that; if I want something in the foreground to stand out then I focus on that; grains of sand and blades of grass often detract from the photo rather than add to it, so after reading Merklinger I realized that using wider apertures that deliberately blur those out of the foreground can make for a more compelling landscape; and finally, using hyperfocal technique and focusing somewhere in the middle is merely focusing on nothing at all and leads to a photo without purpose.

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Re: How Useful is Merklinger's "Object Field" Focusing ?

WilbaW wrote:

Detail Man wrote:

Do you find that focusing directly on the most important subject-matter (even if that exists at "infinity") provides better results as compared to using so-called "Hyperfocal Focusing" techniques ?

Absolutely, without a doubt.

Something that puzzles and troubles me a bit about Merklinger's "Object Field" focusing approach is that it does not appear to take into account the effects of individual human visual acuity when viewing an image (of some particular viewing-size, and from some particular viewing-distance).

Well, you could argue that it doesn't need to because it maximises the possible sharpness where it matters.

Thank you for expressing your thoughts (with which I do agree) ! The rub (where applicable) is in the required foreground resolution (which may be variable in certain situations when a shot is set-up). Allowing for a borrowing (from near-field) - in order to be able to effectuate maximal focus upon a given element at (whatever) distance of the resultant plane-of-focus of - seems best, indeed.

Attention to (and the intentional omitting of when framing a shot) existing near-field subject-matter saves the disadvantages of having (later) to ("heavily") crop-out otherwise desired portions.

What I am wondering is this:

The "price paid" for focusing at "infinity" (as opposed to focusing at some Hyperfocal Distance derived from some given Circle of Confusion diameter) seems to be that the Near Focus Distance (of a "depth of field of acceptable focus") from the camera is doubled in value as a result. Depending upon the intended nature of the composition as it relates to the subject-matter desired to be in "acceptable" focus, this may (or may not) represent a significant sacrifice.

AFAIK, Merklinger only advocates focussing at infinity in very specific circumstances, it's not his method as such, so you may be wondering about something different. (It's a good exercise for the reader to find out when he said to focus at infinity and why.)

Yes. I "focused" (in the rhetorical sense) upon the extreme (being focus at "infinity") to state the (as much as) doubling of the lens-system F-Number necessary to achieve the same Near Focus Distance (from the DOF identities). This consequence can be a factor (depending on distance to any foreground of subject-matter of interest, and the spatial frequency resolution thereof).

It seems that the "sensitivity" of the Near Focus Distance - when comparing focusing at "infinity" and focusing at (many) finite camera-to-subject distancess - is not going to be high ?

The Near Focus Distance increases from the Hyperfocal Distance divided by 2 to being equal to the Hyperfocal Distance itself. Seldom would I be inclined to double the F-Number in order to "buy back" that. The (squared) decrease in sensor-level exposure would seem (to me) to in many cases not be a worthwhile trade in return for a somewhat closer Near Focus Distance.

Using lower valued Focal Lengths (may in some cases) help considerably - but only in cases where the Angle of (and thus Field of) View works out desirably when recorded (without post-cropping).

If the viewer of a printed/displayed image may (as a result of individual visual acuity, viewing-size, and viewing distance) be unable to perceive (some or all of) the increased resolution of the image's far-field subject-matter, then would Merklinger's "Object Field" focusing technique represent a net improvement - or are (some or all of) the alleged advantages of the technique (relating to the resolution of far-field subject-matter) diminished or negated as a result ?

Depends on what you mean by his "technique" - focus at infinity, or focus on the furthest thing that you want to be truely sharp in the image?

I meant Merklinger's "Object Field" focusing technique(s), ranging from "infinity" to closer focusing. Yes, the question was proposed too generally (as answers may correspondingly differ).

My guess is, if the viewer can't see well enough to differentiate levels of sharpness/focus/resolution in the image, it doesn't matter whether you went hyperfocal or beyond. IOW, if the alleged advantages of focussing on the furthest thing you want to be sharp are negated, then so are the alleged (and far more dubious) advantages of focussing at the hyperfocal distance.

It seems that a "developer" (of processed images) is wise to take note, and to factor-in, the intended viewing-size, viewing distance, and (the possibility of) 20/20 visual acuity in viewing.

In intentional, analytic, and predictive cases - where parameters such as operational focal-length, sensor resolution, image-processing characteristics, print/display characteristics, viewing-size, viewing-distance, and 20/20 visual acuity are reflected upon and understood in an operational sense - knowing the lower limits of spatial optical resolution expected (for 20/20 visual acuity) could be valuable knowledge where it comes to any focusing decisions involving focusing in front of the subject-matter of primary interest to the eye (that might alternatively take place).

Where it comes to image enlargement-factor in relation to photosite dimensions, some finite lower limit of a viable "COC diameter" would seem to reasonably apply in the processes of specifying print/display size at presumed viewing-distances. That (minimum) dimension would seem to be some measure of the effective "size" of the photosite-data (as affected in the composite system sense, with lens-system diffraction, any optical filter(s), and (as well) after de-mosaicing.

Below such image dimensions exist known hardware/software/print/display limitations - as opposed to specific limitations in ocular angular resolution at some viewing-size and viewing-distance.

Such things are better determined by measurements than by analysis, as the product of wavelength and F-Ratio is an independent variable in identities describing the effects of de-focusing (due to some COC dimension) combined with diffraction (quite complex), in addition to any optical filtering and photodetector sampling effects, as well as lens-system optical aberrations - where (as I understand it) ray-tracing analysis must be used - in modelling a composite system spatial frequency response (at a RAW-level, and prior to the additional effects of whatever de-mosaicing algorithm may be utilized).

Best Regards,

DM ...

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Re: How Useful is Merklinger's "Object Field" Focusing ?

robert1955 wrote:

WilbaW wrote:

Depends on what you mean by his "technique" - focus at infinity, or focus on the furthest thing that you want to be truely sharp in the image?

If I read him [in the short paper] correctly, he means the latter.

I've had several lively discussions around here with people who are convinced that all Merklinger ever said was "focus at infinity", so I never assume we are talking about the same thing if there's any doubt.

BTW: I don't know where this thread was originally, but I'm a bit a bit curious why this was moved here. This is actually a subject that better fits in a 'photography praxis' forum. Maybe the 'general photo techniques' is intended as such?

Yeah, I don't know where it came from (if I did I would have replied there), but I think it fits here.

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