The Easy View (2 Viewers)

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DOF, properly defined, is just the distance in front and behind a focused object where other closer or more distant objects AT THE SAME POINT in the field continue to be acceptably focused. It has nothing to do with stereopsis or any other "3D" effect, real or imagined. It can be as easily determined with one eye as with two.

Field curvature shifts the distance of a focused point as it moves from the center to edge of the field, but does not change the true DOF at any point along the way. You might compare it to a curved wall 2 meters thick. The ends of the wall may curve toward you in way that makes them 4 meters closer to you than the center of the wall, but that doesn't make the wall 4 meters thick.

Rather than trying to determine DOF by doing something both hard and subjective like detecting the exact distance at which focus is no longer acceptable I prefer to test DOF by comparing the sizes of the large circles of confusion seen about 3-4 meters from an artificial star through telescopes set at infinity focus. The size difference of the blur circles is obvious between telescopes with different DOFs and is unaffected by eyesight acuity, aberrations or field curvature.

"Rather than trying to determine DOF by doing something both hard and subjective like detecting the exact distance at which focus is no longer acceptable, I prefer to test DOF by comparing the sizes of the large circles of confusion seen about 3-4 meters from an artificial star through telescopes set at infinity focus. The size difference of the blur circles is obvious between telescopes with different DOFs and is unaffected by eyesight acuity, aberrations or field curvature."

That is a superb method. Did you devise that on your own?

 

[gweller]

Just a thought.... is the apparent 3d effect in porro binoculars greater than in roofs by simple virtue of the fact that the objective lenses are further apart in porros??

 

[jafritten]

Just a thought.... is the apparent 3d effect in porro binoculars greater than in roofs by simple virtue of the fact that the objective lenses are further apart in porros??

Yes, that's right.

 

[Tringa45]

Rather than trying to determine DOF by doing something both hard and subjective like detecting the exact distance at which focus is no longer acceptable I prefer to test DOF by comparing the sizes of the large circles of confusion seen about 3-4 meters from an artificial star through telescopes set at infinity focus. The size difference of the blur circles is obvious between telescopes with different DOFs and is unaffected by eyesight acuity, aberrations or field curvature.

Or put another way, the size of the circle of confusion is proportional to the magnification (inversely proprtional to eyepiece focal length) and the (dis)information content is prportional to the square of the magnification. Ergo, DoF is prportional to the inverse square of the magnification.
The one human factor that can affect perceived DoF is accommodation, but when one considers that the focussing range of a 10x binocular from 4 m to infinity is equivalent to 25 dioptres, that is probably not a significant factor for most of us.

John

 

[elkcub]

The one human factor that can affect perceived DoF is accommodation ...

There are three parameters of the eye/brain that affect the DOF of the eye-instrument combination: focal length, pupil diameter, and acceptable blur. All three are subject to momentary alteration. The focal length of the eye changes with accommodation, pupil diameter changes with illumination, and acceptable blur changes with the adaptive state of the retina. The visual experience of DOF, therefore, (if one is actually perceived) is both non-static, i.e., dynamic, and idiosyncratic to the individual. Unlike a camera, the DOF of the instrument itself is mathematically undefined because it is optically afocal.

Ed

 

[tenex]

There are three parameters of the eye/brain that affect the DOF of the eye-instrument combination: focal length, pupil diameter, and acceptable blur. All three are subject to momentary alteration. The focal length of the eye changes with accommodation, pupil diameter changes with illumination, and acceptable blur changes with the adaptive state of the retina. The visual experience of DOF, therefore, (if one is actually perceived) is both non-static, i.e., dynamic, and idiosyncratic to the individual.

How is this relevant to a given individual's comparison of two different binoculars in the same conditions?

Most of the perpetual chatter on this subject simply results from misunderstanding the term "depth of field", often confusing it with field curvature, as Henry explained in post 78.

 

[Tringa45]

There are three parameters of the eye/brain that affect the DOF of the eye-instrument combination: focal length, pupil diameter, and acceptable blur. All three are subject to momentary alteration. The focal length of the eye changes with accommodation, pupil diameter changes with illumination, and acceptable blur changes with the adaptive state of the retina. The visual experience of DOF, therefore, (if one is actually perceived) is both non-static, i.e., dynamic, and idiosyncratic to the individual. Unlike a camera, the DOF of the instrument itself is mathematically undefined because it is optically afoc

Ed,

That was merely a supplement to Henry's statement that DoF was unaffected by eyesight acuity.
The afocality of a telescope or binocular does not preclude the mathematical definition of its DoF.
The depth of field of a camera lens is some arbitrarily set value for the acceptable size of the circle of confusion with respect to format, focal length and aperture.
Similarly, the depth of field of a telescope could be mathematically defined as the acceptable size of the circle of confusion in the focal plane of the eyepiece.
I recall reading somewhere that a point source subtending an angle of 3,4 arcmin. would be perceived by most users as sharp.
However, unlike camera users who might be intersted in setting a hyperfocal distance, binocular and telescope users are not interested in the figures and are satisfied with the inverse square law with respect to magnification.
You're not disputing this are you?

John

 

[Maljunulo]

Ed,
I recall reading somewhere that a point source subtending an angle of 3,4 arcmin. would be perceived by most users as sharp.
However, unlike camera users who might be intersted in setting a hyperfocal distance, binocular and telescope users are not interested in the figures and are satisfied with the inverse square law with respect to magnification.
You're not disputing this are you?

John

John

I’m not at all sure how that statement reconciles with the fact that a reasonably good human eye can resolve two point sources of equal brightness separated by an arc minute, or slightly less.

I must admit though, that I am a bit over my head in this discussion.

 

[elkcub]

How is this relevant to a given individual's comparison of two different binoculars in the same conditions?

The relevance is to John's statement in post #84: "The one human factor that can affect perceived DoF..."

I explained that as I see it there are at least three human factors involved. Why is that important when comparing two binoculars? Well, because biological things are not static like a camera would be, they inevitably make for evaluation/measurement problems. Just as an example, if the two instruments only had different transmission distributions, all else being equal, one might expect the observer's pupil size and/or retinal adaptive state to differ when using them. This would thereby affect the perceived DoF of the combined eye/brain-instrument system and the difference incorrectly attributed to an optical difference in the DoF of the binoculars.

That was merely a supplement to Henry's statement that DoF was unaffected by eyesight acuity.
The afocality of a telescope or binocular does not preclude the mathematical definition of its DoF.
The depth of field of a camera lens is some arbitrarily set value for the acceptable size of the circle of confusion with respect to format, focal length and aperture.
Similarly, the depth of field of a telescope could be mathematically defined as the acceptable size of the circle of confusion in the focal plane of the eyepiece.
I recall reading somewhere that a point source subtending an angle of 3,4 arcmin. would be perceived by most users as sharp.
However, unlike camera users who might be interested in setting a hyperfocal distance, binocular and telescope users are not interested in the figures and are satisfied with the inverse square law with respect to magnification.
You're not disputing this are you?

Me, I dispute nothing. Yes, the afocality of a telescope/binocular definitely does not preclude the mathematical assessment of its DoF. In fact, mathematically it is "undefined," as revealed in the attached paper that was posted on BF about 12 yrs. ago (See Eqs. 7 and 8). That's important because this so-called DoF that is attributed to the instrument does not actually exist; it's a misnomer. However, the instrument does modify the DoF of focal systems that are attached to it in an optical chain, e.g., human eyes, cameras, etc. To assess the instrument's DoF impact on the human eye, rather than depending on observers who vary in age and vision health, I favor simply taking pictures of standard scenes using a camera to simulate the eye, and then evaluating the DoF of the resulting images. One can probably assume that typical human assessments would be correlated.

Ed

 

[[email protected]]

Just a thought.... is the apparent 3d effect in porro binoculars greater than in roofs by simple virtue of the fact that the objective lenses are further apart in porros??

The further apart the objective spacing, the more "3D" effect you get! The big Fujinon porro's have great "3D."

 

[tenex]

Just as an example, if the two instruments only had different transmission distributions, all else being equal, one might expect the observer's pupil size and/or retinal adaptive state to differ when using them.

Can we not assume that "DoF" comparisons are done in broad daylight when the pupil is fully contracted, and roughly how large a transmission difference between instruments would be needed in such circumstances for a change in adaptation to affect perception of blur?
(Just to be clear, I'm questioning not the technical correctness, but the practical relevance.)

 

[elkcub]

Hi Tenex,

In times past several of us have enjoyed lengthy and informative discussions about binocular DOF. I learned a lot, at least on an abstract basis, and since the discussions are still available I'd recommend the following: (there are others)

Depth of field in afocal systems

Depth of field in afocal systems

It has been annoying to me that I haven't been able to fully understand what determines the depth of field (DOF) of afocal systems. A recent experiment with a diaphragm module has helped me comprehend this tricky subject. I believe I'm fairly close to the truth but claiming that this is the last...

www.birdforum.net

depth of field

depth of field

Absolutely - we are lacking high quality 6 power binoculars. Even the compact binoculars of the high end manufacturers are usually 8x or 10x - although here particularly a lower power would be of advantage (wider exit pupil, easier to held steady, and, of course, a large dof). This is entirely...

www.birdforum.net

Depth of field / Flat field

Depth of field / Flat field

Is flat field the opposite DOF ?

www.birdforum.net

However, more to your point about "practical relevance," to be honest I don't use depth of field as an evaluation criterion. That's because I accept that it's simply a perceptual correlate of magnification.

Cheers,
Ed

 

[[email protected]]

Hi Tenex,

In times past several of us have enjoyed lengthy and informative discussions about binocular DOF. I learned a lot, at least on an abstract basis, and since the discussions are still available I'd recommend the following: (there are others)

Depth of field in afocal systems

Depth of field in afocal systems

It has been annoying to me that I haven't been able to fully understand what determines the depth of field (DOF) of afocal systems. A recent experiment with a diaphragm module has helped me comprehend this tricky subject. I believe I'm fairly close to the truth but claiming that this is the last...

www.birdforum.net

depth of field

depth of field

Absolutely - we are lacking high quality 6 power binoculars. Even the compact binoculars of the high end manufacturers are usually 8x or 10x - although here particularly a lower power would be of advantage (wider exit pupil, easier to held steady, and, of course, a large dof). This is entirely...

www.birdforum.net

Depth of field / Flat field

Depth of field / Flat field

Is flat field the opposite DOF ?

www.birdforum.net

However, more to your point about "practical relevance," to be honest I don't use depth of field as an evaluation criterion. That's because I accept that it's simply a perceptual correlate of magnification.

Cheers,
Ed

Exactly. I think you are overcomplicating DOF. It is directly correlated to magnification, and that is really all you have to be concerned with.

 

[tenex]

In times past several of us have enjoyed lengthy and informative discussions about binocular DOF. I learned a lot, at least on an abstract basis, and since the discussions are still available I'd recommend the following: (there are others)

All these discussions seem to repeat similar questions and answers, go around in circles, get sidetracked in confusions between "depth of field" vs "perception of depth" etc, argue about focal vs afocal, speculate about and then dismiss focal lengths, and ultimately fail to identify any property of a binocular except magnification that would cause different models to show noticeably different depth of field (properly understood) to the same observer in daylight (where aperture/exit pupil is not a limiting factor).

Could some people actually be noticing small differences in magnification between instruments of the same nominal power? (It is 1/m^2...)

More fundamentally, it may be a mistake to try to deduce some general explanation from theory before being sure what the alleged phenomenon is, and instead observers should first be more precise about exactly what difference they claim to see between which models, and in what circumstances (distance, lighting, etc).

[Edit: Allbinos measures magnification, but doesn't seem to have reviewed any of the four 8x32s compared by Steve in post 10 of that first thread.]

 

[[email protected]]

Here are some interesting threads on DOF from Cloudy Night's and a comment by Prof. EdZ and Everlasting Sky. It is more complicated than you think, apparently.

Depth of Field ? - Binoculars - Cloudy Nights

Page 1 of 2 - Depth of Field ? - posted in Binoculars: What optical parameters determine a binoculars Depth of Field?It would seem to be factor(s) besides magnification, objective diameter and effective exit pupil. For example, there are several web comments on the remarkable DOF of the Fujinon...

www.cloudynights.com

Why Such Incredible Depth of Field On My Fuji 7x50? - Binoculars - Cloudy Nights

Why Such Incredible Depth of Field On My Fuji 7x50? - posted in Binoculars: Before I ask the question I am about to ask I want to mention that I am quite familiar with f-stops and iris size. I am a long time amateur photographer and have used Canon EOS when there was no digital. So I get the...

www.cloudynights.com

"Depth of Field is the range of objects from foreground to background seen in focus without moving the focus dial. Longer focal lengths will provide greater depth of field. Further distance from the object will provide greater depth of field. It has no application at all in astronomy, objects are focused at infinity. It is very important in terrestrial use. Although I'm sure a certain amount of depth of field is present, I wouldn't be surprised that people misinterpret sharpness of image and brightness of image combined to present what appears to be a greater depth of field. A binocular with a less sharp image and less bright image may not appear to have as great a depth of field. As an example, a 7x50 used in daylight vs. a 7x35 used in daylight. The following is from the article on Affect of Eye Pupil on Binocular Aperture.[What happens in low light terrestrial viewing, where many seem to prefer a larger exit pupil because it seems brighter? Now we need to go back to the cardinal rule that states exit pupil controls effective aperture. There would be no more light delivered by either binocular if eye pupil is 2.5 mm, BUT, as seen through a 2.5 mm eye pupil, there would seem to be a difference in the two binoculars, and you might be able to see this difference. The 10x25 binocular is using the entire objective lens, and we have seen from vignette studies, many (if not all) binocular systems block (vignette) portions of the light from the periphery of the objective lens. The 10x25 is using the entire diameter of the lens to light the exit pupil, and the light from the outer portions of the objective is reduced in the exit pupil due to vignette. Not all the light gathered by the 10x25 reaches the eye. Most vignette studies show that approximately the central 50% of an objective lens provides 100% illumination of the exit pupil. The light delivered from the area outside the central 50% of the objective does not all reach the exit pupil. In the 10x50 binocular, stopped down by the daylight contracted eye pupil to 10x25, only the central 50% of the objective is putting light into the exit pupil. The key is this 2.5 mm exit pupil is 100% illuminated from the central portion of a stopped down 50 mm lens. A stopped down 10x50 is providing a lot more illumination to the same size 2.5 mm exit pupil than a full aperture 10x25. That would account for a significant difference in apparent brightness between the two, even though both situations have a 2.5 mm exit pupil. As a bonus, that same 10x50 binocular will serve the user better under lower light conditions when eye pupil is enlarged to possible 3 mm or 4 mm. Same analogy can be made with the 7x50. The more central area of the objective is being used to provide the light to the eye. This implies better sharpness of image and greater light distribution across the eye's entrance pupil. The effect this has is a much more noticeable image. While this is not the sole factor, this may be interpreted as greater depth of field. It is definitely contributing to it."

"The Fujinon 7x50 has been my favorite binocular for 22+ years. I never touch the focus and each barrel it is left permanently on 0 diopters. Everything is is always in focus. That's what I call civilized. As an aside, I tried a pair of Kowa Genesis 8x33 earlier this year... had to return them within a few days. Every target required re-focusing. A squirrel, that tree just over, that wall, that building, that plane, that mountain. Horrific eye fatigue quickly resulted. Very... uncivilized. Back to 7x50 for daytime. The Kowa was 590g in weight VS 1450g or thereabout for the Fuji... I had high hopes for the Kowa! So light weight with such good ergonomics. But for me, I consider such constant re-focus performance utterly unusable & unacceptable. 7x50 has given me unreasonable expectations, I suppose. Of course, there must be many other good lightweight roof's in that size which do not require endless refocus? Too lazy to seek the answer... pass the 7x50, please!"

 

[henry link]

Here are some interesting threads on DOF from Cloudy Night's and a comment by Prof. EdZ and Everlasting Sky. It is more complicated than you think, apparently.

No Dennis, it's not more complicated than we think. EdZ was more wrong than you think. His misconceptions about "vignetting of the exit pupil" were notoriously wrong and eventually corrected by others at Cloudy Nights. Everlasting Sky's notion (if he was even serious) that IF 7x50s are the best daylight binoculars because they never need refocusing is so obviously wrong that it doesn't need discussion.

 

[Troubador]

No Dennis, it's not more complicated than we think. EdZ was more wrong than you think. His misconceptions about "vignetting of the exit pupil" were notoriously wrong and eventually corrected by others at Cloudy Nights. Everlasting Sky's notion (if he was even serious) that IF 7x50s are the best daylight binoculars because they never need refocusing is so obviously wrong that it doesn't need discussion.

It sounds as though ES actually believed those stories told by some brands about 'auto-focusing' binoculars......

Lee

 

[[email protected]]

This discussion is concerning DOF in cameras. How much of this relates to binoculars? It seems some of it would.

Depth of Field and Depth of Focus

Are you getting depth of field and depth of focus confused? Discover the differences and how to distinguish the two from one another at Edmund Optics.

www.edmundoptics.com

 

[[email protected]]

No Dennis, it's not more complicated than we think. EdZ was more wrong than you think. His misconceptions about "vignetting of the exit pupil" were notoriously wrong and eventually corrected by others at Cloudy Nights. Everlasting Sky's notion (if he was even serious) that IF 7x50s are the best daylight binoculars because they never need refocusing is so obviously wrong that it doesn't need discussion.

You're being a little harsh on EdZ's comment's. Perhaps his "vignetting of the exit pupil" was not totally correct, a lot of his other discussion was helpful explaining DOF and shouldn't be totally dismissed. There have been many, many comments about the Fujinon 7x50 FMT-SX binoculars not needing much refocusing beyond 90 feet once the diopters are set, and I use them myself that way, so I know for a fact you are wrong on that point. Have you ever even used the Fujinon FMT-SX 7x50 porro?

 

[henry link]

I used a pair of Fujinon 7x50 FMT-SX for about 6 years. Still have seven 7x50 Porros including my personal favorite: the Nikon Prostar. I don't use any of them for birding in daylight, particularly not the IF models.