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Depth of Field - I am confused (1 Viewer)
- Thread starter jafritten
- Start date
Hermann
Well-known member
Zeiss first used the T* designation for the multicoatings they started using on their Dialyts. That was in the early 1980s, more than 40 years ago now. Even at the time there were apparently differences between the coatings used on different models, perhaps because of different glass types used in different models. The coatings on the 7x42 BGAT* for instance looked quite different from the ones on e.g. the 8x30 BGAT* and the 10x40 BGAT*.
I have no doubts that the coatings Zeiss uses today are quite different from those used in the early years. (They are for instance IMO much more scratch resistant than the earlier coatings.) I also don't doubt Zeiss tweaks the coatings without making a big fuss about it whenever they believe the new coatings offer some advantages. That's what all the major manufacturers do AFAIK.
BTW, I personally wouldn't be bothered if they dropped the T* designation altogether, just like they dropped the P designation after a few years. If I buy a binocular I don't buy any letters, I buy a binocular. And with a maker like Zeiss (or Leica, or Swarovski, or Nikon, or Canon ...) I firmly believe I can rely on them using coatings that are state of the art. The exception may be low-end binoculars like the Terras.
Hermann
Paultricounty
Well-known member
I think you have to reevaluate on this one. We actually did a nice little test using a half a dozen specific binoculars of the same magnification with similar and different objective of sizes. We focused on specific objects close and far to see if there was any difference. I think we also threw in a different magnification just for giggles.
Im looking for the post. If anybody knows where it is please share the link.
Paultricounty
Well-known member
Only if he’s a scientist 🤣
Paultricounty
Well-known member
What about Chyna 🤭Discussing is easier than investigating. It does not requires scientific competence, tools, etc. Just good English.
If someone investigate, are we ready to trust the results?
This is a forum, and not a scientific one.
Let’s enjoy what we have.
From this thread:
Therefore:
It is very possible to be right, but your experience cannot be extrapolated to all binoculars 10x. Nor for the same binocular utilized by different humans.
Therefore:
What is your definition of "the same"? Do you measured it, do you have numbers? Or just a guesstimate?
It is very possible to be right, but your experience cannot be extrapolated to all binoculars 10x. Nor for the same binocular utilized by different humans.
Just a guesstimate - not extrapolating to anything else, just a quick look with my two 10x binos. When I used my 8x56 Dialyt, they seemed to have enormous DOF, more than my 8x42's. Will have to test those two and do some more comparing.
Elkhornsun
Well-known member
What we perceive as DOF is really the clarity of the image presented to our eyes and this depends on the contrast and resolution of the binoculars. There does not appear to be an industry standard for measuring either contrast or resolution as is done for camera lenses so it becomes a subjective matter with a person alternating between two binos and stating their option.
With lenses that provide exceptional resolution and contrast I have found that when viewing a print that it looks like one is at the location and viewing it first hand. This is rare and I have only encountered it with high end medium format cameras and lenses and one underwater lens - Nikonos 15mm underwater only lens.
With lenses that provide exceptional resolution and contrast I have found that when viewing a print that it looks like one is at the location and viewing it first hand. This is rare and I have only encountered it with high end medium format cameras and lenses and one underwater lens - Nikonos 15mm underwater only lens.
The DOF I'm talking about is not clarity, contrast, or resolution. It refers to focus. Whether objects in the distance are in focus or out of focus. For this test I focus on the fence in my backyard 100 feet away and then check the tree trunks in front and behind and see how many of them are in focus. With 7x some of the trees in front and behind are in focus along with the fence - at 10x, the trees are out of focus - only the fence is still focused.
Sounds like a more fascinating subject for a thread than this one even! Do you know enough about the concept to start a thread on it?
Many of these conversations become more interesting as I read about them, but very often I'll stop following a thread when I realize that regardless of its importance to the the subject of optics, they're boring to me.
This concept of increasing depth of field through the usage of fresnel components seems like it would also be of interest to others who have participated in threads like this.
The discussions I had on these lenses were private and I don't want to get into the work that companies are involved with.
So no, I'll leave this topic to someone else if they have non private knowledge.
I just thought I should mention that this topic is more complex than the opinions in the above posts.
Increased depth of field is not a new concept.
Regards,
B.
So no, I'll leave this topic to someone else if they have non private knowledge.
I just thought I should mention that this topic is more complex than the opinions in the above posts.
Increased depth of field is not a new concept.
Regards,
B.
tenex
reality-based
Some camera lenses (e.g. Nikkor 300/500mm PF) use a "Phase Fresnel" element to reduce overall bulk. I gather that it has inverse properties of refraction (bringing longer wavelengths to a closer focus) which corrects CA more efficiently than combinations of conventional lenses. But it doesn't seem obvious how this could increase DOF, and I haven't heard that it does in these lenses. Photographers often want less of it at such focal lengths.
looksharp65
Well-known member
The DOF discussion has not really tempted me, for a number of reasons, maintaining mental sanity being one. With this comment, I will present a few statements that may challenge someone's deeply rooted knowledge or prejudices. I offer them as means to broaden the understanding of the depth-of-field concept.
Well aware that there may be details where I draw incorrect conclusions, I'd with certainty say most of all this is true.
First, I'll deal with focal systems as opposed to afocal systems. Focal systems project a real image onto a surface, usually film or a digital sensor. The science of depth-of-field in focal systems is very thoroughly researched. It is not unusual with camera lenses with coloured lines for different apertures, to aid when setting focus on the hyperfocal distance in order to achieve maximum DOF.
The result is convincing when you look at a print where your eyes can roam over a frozen-in-time two-dimensional representation of a three-dimensional reality to see full edge sharpness, apparently at a considerably closer distance than the sharp horizon in the distant.
The actual size of the aperture (not the f/ number) and the imaging scale are the only two quantifiable factors to decide the DOF, unless a large format camera with a tilting film plane is used.
You may argue that the lens's curvature of field also could serve to increase DOF. This is not necessarily wrong, but is it DOF?
This brings us to the first point that needs clarification, or rather an agreement upon where to assess DOF – using test targets as close as possible to the optical axis, or targets placed on the ground plane where closer targets (usually) will appear increasingly closer towards the lower part of the image.
The latter can mean a huge difference in apparent DOF when compared to the first method, should the lens have considerable curvature of field. I own an '80s Mamiya roof prism that's virtually progressive, the edges focus a lot closer than the center.
It is very important to be clear that real aperture size and imaging scale are the determining factors for DOF. A real world example would be an image shot with a 100 mm f/2.8 at a certain distance and at full aperture, compared to another shot with a 50 mm f/1.4 under the same circumstances.
If prints are made, and the ”50 mm” prints are printed twice as large, the size of objects in the image will not only be identically large, but also exhibit the same apparent DOF. Grain or digital noise will of course differ. Conversely, a print from a camera with a small sensor will exhibit a deeper DOF despite the same image scale, but then because of the small aperture of the small lens with its short focal length. A smaller aperture produces smaller circles of confusion, and the smaller, the sharper appears the image. (Here lies the only reason small binoculars can produce a greater perceived DOF, namely when the instrument's exit pupil is smaller than the observer's pupil and acts as a mask.)
End of the part dealing with focal instruments.
This second part may appear in stark contrast to the first part, that's dealing with (largely) quantifiable factors. I claim there isn't really a thing as depth-of field. Rather, DOF is, actually like anything concerning vision and perception, a hallucination the majority agrees is useful.
It relies upon standardised visual acuity, and is essentially defined as a defocus too small to be detected by a normal eye. This is extremely important to keep in mind.
DOF is (again) depending on image scale and the observer's visual acuity, and is inversely proportional to both. 'The better we see, the worse we see'.
If this seems counter-intuitive, imagine smearing vaseline on your ocular lens. The general sharpness will of course plummet, but it is the central sharpness that takes the big hit. Outside the central macula of the retina where visual acuity decreases rapidly going further out on the peripheral retina, there's not so much to lose. So the difference in acuity, or focus, between the worse and the better parts, is not as big, which in turn means DOF is greater when VA, or the instrument's resolution, or both, are worse. This also applies to detection of resolution differences between central and peripheral parts of lenses or lens systems, i.e. across the image plane.
Conversely, on the opposite side of the scale, we have the situation where an observer has an insanely high visual acuity. VA is essentially the same thing as resolution, and is defined by the smallest gap between lines that can be seen. If the point of absolute focus contains the absolutely smallest line pair this observer can see, they will also fail to detect it with a minimal amount of defocus (due to distance differences), while an observer who can only resolve a bigger line pair may also be able to detect their line pair despite a slight defocus. This is because the circle of confusion, that has an absolute size determined by the aperture and dioptrical defocus, is relatively smaller compared to the bigger line pair than to the small line pair.
Increased magnification will reveal defocus regardless of whether using telescopes, microscopes, shortened viewing distance, zooming on a screen or printing a larger print. Even going closer to a print will show lack of focus. Naturally, the grain or pixel size puts a hard stop somewhere along the line.
A high visual acuity offers the possibility to detect defocus and otherwise subpar performance of an instrument. However, the observer may also be able to dismiss these minute differences and blend it all to a ”clearly sharp enough” judgement. 'The better you see, the worse you see' holds a reality when critically approaching the limits, but in daily life, good vision simplifies things as there's a wide margin.
Keeping the counterintuitive nature of DOF, and the implications of DOF being a perceptual rather than a technical concept, in mind, I'll now finally with a few words mention apparent DOF in afocal instruments.
This subject has been penetrated thoroughly in many good posts and then again others, but I feel the two parts I mentioned above have largely been omitted.
The afocal instrument's objective lens creates a real image, that could have been projected on a surface, but instead we watch it with a loupe, the eyepiece. Generally speaking, we let diverging or parallel rays enter the objective, and we collect parallel, or sometimes diverging rays leaving the ocular lens. For objects near infinity (optically speaking), it's parallel rays in and parallel rays out, unless you're an uncorrected myope, where you must focus the instrument beyond infinity.
Typically, we can see at infinity because rays are parallel, and closer because accommodation ensures that the diverging rays from nearby objects are refracted in the lens crystallina, not to parallel, but converging to a real image on the retina just as parallel rays from infinity are after entering the eye.
We can not process converging rays from outside the eye, such as those that form a real image.
As I showed above, DOF is a dirty concept. Initially, it may seem technical, but it is entirely perceptual, and, as such, entirely depending on the observer. There is to my knowledge no evidence that focal ratio of an afocal instrument has any quantifiable effect on the perceived DOF.
The evasive nature of DOF as a perceptual concept, in particular weighing in the individual's continual accommodation effort, their likewise incessantly changing pupil diameter, the illumination, whether or not a big AFOV produces a smaller pupil due to greater area of the retina getting illuminated, if the individual has astigmatism, has or has not different refractive status of the right and the left eye, the eye's axial length, whether or not spectacles are used, or whether or not the diopter is used, what focussing technique they use (approaching the focus target from near or from far away), and so on ad nauseam, makes this impenetrable.
If, theoretically, photography through binoculars was performed, if the photos all were taken near the center of the field, and then any minuscule DOF differences could be detected that consistently followed the configurations, e.g. 10x25 vs 10x50, with several samples of each configuration, each model and each brand, it would actually still be quite useless, because in the end, the ever-changing compound effect of our eyes, our perception, our brain, our current physical and mental condition would trump those differences with several magnitudes. As far as I know, no convincing arguments of real DOF differences within a set magnification have been presented to date.
Discussion on DOF usually means we bite off more than we can chew. Discussing colour reproduction or rolling ball is a child's play compared to depth of field.
I have no intention to get the last word, but even this post, that cost me a Saturday's evening, is no more than a ripple on a deep ocean of ignorance, and I have no expectation that the shore will appear before our eyes. Maybe I helped someone look in the right direction.
//L
Well aware that there may be details where I draw incorrect conclusions, I'd with certainty say most of all this is true.
First, I'll deal with focal systems as opposed to afocal systems. Focal systems project a real image onto a surface, usually film or a digital sensor. The science of depth-of-field in focal systems is very thoroughly researched. It is not unusual with camera lenses with coloured lines for different apertures, to aid when setting focus on the hyperfocal distance in order to achieve maximum DOF.
The result is convincing when you look at a print where your eyes can roam over a frozen-in-time two-dimensional representation of a three-dimensional reality to see full edge sharpness, apparently at a considerably closer distance than the sharp horizon in the distant.
The actual size of the aperture (not the f/ number) and the imaging scale are the only two quantifiable factors to decide the DOF, unless a large format camera with a tilting film plane is used.
You may argue that the lens's curvature of field also could serve to increase DOF. This is not necessarily wrong, but is it DOF?
This brings us to the first point that needs clarification, or rather an agreement upon where to assess DOF – using test targets as close as possible to the optical axis, or targets placed on the ground plane where closer targets (usually) will appear increasingly closer towards the lower part of the image.
The latter can mean a huge difference in apparent DOF when compared to the first method, should the lens have considerable curvature of field. I own an '80s Mamiya roof prism that's virtually progressive, the edges focus a lot closer than the center.
It is very important to be clear that real aperture size and imaging scale are the determining factors for DOF. A real world example would be an image shot with a 100 mm f/2.8 at a certain distance and at full aperture, compared to another shot with a 50 mm f/1.4 under the same circumstances.
If prints are made, and the ”50 mm” prints are printed twice as large, the size of objects in the image will not only be identically large, but also exhibit the same apparent DOF. Grain or digital noise will of course differ. Conversely, a print from a camera with a small sensor will exhibit a deeper DOF despite the same image scale, but then because of the small aperture of the small lens with its short focal length. A smaller aperture produces smaller circles of confusion, and the smaller, the sharper appears the image. (Here lies the only reason small binoculars can produce a greater perceived DOF, namely when the instrument's exit pupil is smaller than the observer's pupil and acts as a mask.)
End of the part dealing with focal instruments.
This second part may appear in stark contrast to the first part, that's dealing with (largely) quantifiable factors. I claim there isn't really a thing as depth-of field. Rather, DOF is, actually like anything concerning vision and perception, a hallucination the majority agrees is useful.
It relies upon standardised visual acuity, and is essentially defined as a defocus too small to be detected by a normal eye. This is extremely important to keep in mind.
DOF is (again) depending on image scale and the observer's visual acuity, and is inversely proportional to both. 'The better we see, the worse we see'.
If this seems counter-intuitive, imagine smearing vaseline on your ocular lens. The general sharpness will of course plummet, but it is the central sharpness that takes the big hit. Outside the central macula of the retina where visual acuity decreases rapidly going further out on the peripheral retina, there's not so much to lose. So the difference in acuity, or focus, between the worse and the better parts, is not as big, which in turn means DOF is greater when VA, or the instrument's resolution, or both, are worse. This also applies to detection of resolution differences between central and peripheral parts of lenses or lens systems, i.e. across the image plane.
Conversely, on the opposite side of the scale, we have the situation where an observer has an insanely high visual acuity. VA is essentially the same thing as resolution, and is defined by the smallest gap between lines that can be seen. If the point of absolute focus contains the absolutely smallest line pair this observer can see, they will also fail to detect it with a minimal amount of defocus (due to distance differences), while an observer who can only resolve a bigger line pair may also be able to detect their line pair despite a slight defocus. This is because the circle of confusion, that has an absolute size determined by the aperture and dioptrical defocus, is relatively smaller compared to the bigger line pair than to the small line pair.
Increased magnification will reveal defocus regardless of whether using telescopes, microscopes, shortened viewing distance, zooming on a screen or printing a larger print. Even going closer to a print will show lack of focus. Naturally, the grain or pixel size puts a hard stop somewhere along the line.
A high visual acuity offers the possibility to detect defocus and otherwise subpar performance of an instrument. However, the observer may also be able to dismiss these minute differences and blend it all to a ”clearly sharp enough” judgement. 'The better you see, the worse you see' holds a reality when critically approaching the limits, but in daily life, good vision simplifies things as there's a wide margin.
Keeping the counterintuitive nature of DOF, and the implications of DOF being a perceptual rather than a technical concept, in mind, I'll now finally with a few words mention apparent DOF in afocal instruments.
This subject has been penetrated thoroughly in many good posts and then again others, but I feel the two parts I mentioned above have largely been omitted.
The afocal instrument's objective lens creates a real image, that could have been projected on a surface, but instead we watch it with a loupe, the eyepiece. Generally speaking, we let diverging or parallel rays enter the objective, and we collect parallel, or sometimes diverging rays leaving the ocular lens. For objects near infinity (optically speaking), it's parallel rays in and parallel rays out, unless you're an uncorrected myope, where you must focus the instrument beyond infinity.
Typically, we can see at infinity because rays are parallel, and closer because accommodation ensures that the diverging rays from nearby objects are refracted in the lens crystallina, not to parallel, but converging to a real image on the retina just as parallel rays from infinity are after entering the eye.
We can not process converging rays from outside the eye, such as those that form a real image.
As I showed above, DOF is a dirty concept. Initially, it may seem technical, but it is entirely perceptual, and, as such, entirely depending on the observer. There is to my knowledge no evidence that focal ratio of an afocal instrument has any quantifiable effect on the perceived DOF.
The evasive nature of DOF as a perceptual concept, in particular weighing in the individual's continual accommodation effort, their likewise incessantly changing pupil diameter, the illumination, whether or not a big AFOV produces a smaller pupil due to greater area of the retina getting illuminated, if the individual has astigmatism, has or has not different refractive status of the right and the left eye, the eye's axial length, whether or not spectacles are used, or whether or not the diopter is used, what focussing technique they use (approaching the focus target from near or from far away), and so on ad nauseam, makes this impenetrable.
If, theoretically, photography through binoculars was performed, if the photos all were taken near the center of the field, and then any minuscule DOF differences could be detected that consistently followed the configurations, e.g. 10x25 vs 10x50, with several samples of each configuration, each model and each brand, it would actually still be quite useless, because in the end, the ever-changing compound effect of our eyes, our perception, our brain, our current physical and mental condition would trump those differences with several magnitudes. As far as I know, no convincing arguments of real DOF differences within a set magnification have been presented to date.
Discussion on DOF usually means we bite off more than we can chew. Discussing colour reproduction or rolling ball is a child's play compared to depth of field.
I have no intention to get the last word, but even this post, that cost me a Saturday's evening, is no more than a ripple on a deep ocean of ignorance, and I have no expectation that the shore will appear before our eyes. Maybe I helped someone look in the right direction.
//L
Last edited:
What these arguments can be?
And what differences are real? How you determine the "realness" of differences?
It seems to me that this discussion has become one of perceived depth-of-field, rather than discussion of an optical property, which can be measured, and which is determined by the relevant physics.
Thus, we have (once again) fearlessly stepped off the path, and are wandering in the swamp of subjectivity.
Thus, we have (once again) fearlessly stepped off the path, and are wandering in the swamp of subjectivity.
How this optical property can be mesured for afocal optics?
The post implies the perceived DOF cannot be measured. It is so?
