Depth of Field - I am confused (2 Viewers)

[Binastro]

I have had eight or more Tento 20x60 binoculars.

None were really sharp to me although other experienced observers liked them.

The reason is that I had one of the dozen made for Jim Hysom specially by hand and selected for experienced astronomers.

Now, one of two things can happen.
Because the normal Tento 20x60s are not very sharp, the in focus image is so so.
Moving out of focus one can perceive that the depth of field is less than the specially good one, or the DOF is greater because the images are still not very good.

However, even the specially made one is nowhere near as good as the Zeiss 20x60S with the stabilizer off.

In my case, none of the Tento 20x60s is as bad as my two Pentax 20x60s.

Then there is actual observation.
Any hand held 8x binocular is likely to be inferior to an 8x IS binocular that works properly.

If a bird is still, then the maximum detail can be seen as one can use central vision for extended periods.

But if the bird is flying the image is a blur, central vision may not be used, only glimpses of good definition might be seen and the resolution may be half or a third of a still bird.

In this case DOF may be all messed up, as nowhere is the bird sharp.
A good IS binocular that pans well may be far more effective.

So, I think that DOF depends heavily on the actual optical quality of the binocular.

I have looked through hundreds of binoculars and the resolution varies enormously.
In some the stars are bloated even in very well made binoculars.
In others the stars are tiny and sharp.

Both the binocular and ultimately the observer influence DOF, and perceived DOF and measured DOF may be quite different.

As said by some above, this is a difficult subject.

Regards,
B.

 

[looksharp65]

In principle, once we got the raw numbers, it is possible to calculate the range of distances in which the image appears in focus to the observer. We need the accommodation width of that observer, the diameter of the effective exit pupil (the smaller one of both, the exit pupil and the eye pupil), and the magnification. Acuity plays a role, indeed, since it defines the circle of confusion that is tolerable to the individual observer, but this is eventually a minor effect because the observer will always use his accommodation to get the object sharp, or else he would have to re-focus by a tiny amount. A reduction of the tolerable circle of confusion would require just a minor refocusing of the instrument with little influence on the actual range of the sharp image.

Now, the width of accommodation of a given individual is not necessarily a fixed quantity, but dependent on his state of exhaustion, on the presence of drugs such as coffee or alcohol and on general health conditions, perhaps on the ambient temperature (the eye lens is less flexible in freezing temperatures). Then, the DOF is defined at the center of field, since off-center aberrations would affect image sharpness. In particular field curvature can create that 'vary-focal' effect that allows off center objects in the foreground to be sharp even though they are technically outside the DOF. The observer then believes to experience an enhanced DOF and draws incorrect conclusions.

It is a difficult business, and the repeated discussions on this topic reflect these difficulties. In real life applications, however, there is little to worry about: Just remember that low magnifications significantly enhance the DOF, and that in some situations a strong field curvature can be exploited to use the vary-focal effect if you want to survey the landscape from your observation site.

Cheers
Holger

Hi Holger
Accommodation can only be positive, which means that only the circles of confusion that are closer to the observer as compared to the main plane of focus may be reduced in size. Of course, if the width of accommodation is wide, as with children and young people, the binocular could be focused at a farther distance and accommodation used for every nearer object, such as with fixed focus binoculars. And like in photography, DOF increases rapidly with the plane of focus further away from the sensor.
Bottom line: accommodation cannot be used to improve sharpness beyond the plane of focus (negative accommodation is a myth)
Furthermore, adding accommodation into the discussion emphasizes the fact that DOF is a perceptual phenomenon, highly subjective and individual-dependent.
It underlines that DOF isn't a property of the instrument, other than it generally is inversely proportional to the magnification, as we all agree.

The lens inside the eye will not be affected by low outside temperature. There are some reports of corneal injury due to extreme cold. The lens, being embedded inside the eye with aqeous humor heated by a plethora of blood vessels in the uvea, will keep the body temperature.
Incidentally, at the other end of the spectrum, it is safe for fire fighters to use contact lenses. The eye will be well protected against the heat and will not be the first body part to give in.

Re the instruments with curvature of field; I mentioned my Mamiya roof with a very excessively curved field. It's like a circular progressive lens. Obviously this doesn't qualify as depth of field. Or maybe it does, because DOF seems to mean anything and nothing.
All in all, we concur at large.

//L

 

[tenex]

I cannot understand the point of continual references to subjectivity, psychophysics, etc on this topic. We are talking not about different individuals' perceptions using the same instrument, but the other way around.

I hate to repeat myself but am obliged to, given responses like "because perception is subjective". So I'll elaborate:

If we want to know why two different individuals claim to see significantly different DOF in the same binocular, we can appeal to a variety of subjective factors mentioned above... although they seem unlikely to explain such large differences, and judging by forum posts, it still remains quite likely that one person simply has some misunderstanding, as obviously happens all the time.

If however we want to know why some individual claims that two different binoculars of the same magnification have significantly different DOF, as they should not, and as others find they do not, we cannot appeal to subjective differences of individual perception, because we are trying to understand a single individual's comparison of the instruments, involving no difference in subjective factors. Either some real difference in magnification or optical quality(?) is responsible -- in which case most (if not all) observers should perceive more or less the same difference for the same reason despite modest variation in subjective perception -- or the outlier made some simple methodological error (like different focus distances) or must once again have misunderstood the definition of DOF, and registered the effect of some other factor like field curvature instead.

It cannot be argued that if their evalution of each binocular separately is subjective, their comparison of the two is therefore also purely subjective. Even a subjective perception of difference requires an objective explanation, and DOF threads like this keep being provoked by claims of just such differences, so talking about subjectivity doesn't help.

 

[Paultricounty]

I hate to repeat myself but am obliged to, given responses like "because perception is subjective". So I'll elaborate:

If we want to know why two different individuals claim to see significantly different DOF in the same binocular, we can appeal to a variety of subjective factors mentioned above... although they seem unlikely to explain such large differences, and judging by forum posts, it still remains quite likely that one person simply has some misunderstanding, as obviously happens all the time.

If however we want to know why some individual claims that two different binoculars of the same magnification have significantly different DOF, as they should not, and as others find they do not, we cannot appeal to subjective differences of individual perception, because we are trying to understand a single individual's comparison of the instruments, involving no difference in subjective factors. Either some real difference in magnification or optical quality(?) is responsible -- in which case most (if not all) observers should perceive more or less the same difference for the same reason despite modest variation in subjective perception -- or the outlier made some simple methodological error (like different focus distances) or must once again have misunderstood the definition of DOF, and registered the effect of some other factor like field curvature instead.

It cannot be argued that if their evalution of each binocular separately is subjective, their comparison of the two is therefore also purely subjective. Even a subjective perception of difference requires an objective explanation, and DOF threads like this keep being provoked by claims of just such differences, so talking about subjectivity doesn't help.

In my informal test three of us seen the same thing with DOF in all binoculars of the same magnification, we also we’re of different age groups and under different lighting conditions. I didn’t think about weather conditions like very hot and very cold , which may have an effect as someone here has said , thus possibly altering some results. My hypothesis as to why some see differences in the same magnification binos is because , some are going by memory, some are confusing different optical traits like immersive and three-dimensional image quality, flat field and curved field differences , some who just spent money and have to legitimize the new Bino purchase ( best DOF). Then others who have made statements don’t want to admit that they might’ve been wrong, that’s a little bit human nature.

I wonder if it’s possible to see a difference in DOF in two binoculars advertised as the same magnification but are slightly off. Let’s say we have two 8x42’s and one is 7.85x and the other 8.1x. My guess is that it could be measured but most likely would not be seen by the eye.

Paul

 

[Binastro]

People have very different observational skills.

There is the placebo effect.

One can only see through ones own eyes.

One cannot see through another person's eyes, and one cannot interpret the image seen through another's eyes or even ones own eyes.

To me curved field is a brother of DOF, and cannot reasonably be separated when it comes to actual viewing.

Regards,
B.

 

[looksharp65]

You know, we don't believe what we see. That's not how it works. The opposite is true, though - we see what we believe. But I have a very effective and simple method to challenge both the first group and the second group (those who admit to see what they believe).

I have two hands. On each hand I have a thumb, so my total number of thumbs is two, and two is the number of my thumbs.

But I can easily make nearly everybody admit that it looks that I have three thumbs, and not by sneaking in any other body part. They admit they see three thumbs.

The first group must, in order to be coherent and consequent, accept that I actually have three thumbs. Or else, abandon their paradigm that they believe what they see

The second group, who obviously neither believe I have three thumbs, must admit to see three thumbs without actually believing it.

It is all about what we choose to ignore. And we all ignore incredible amounts of visual information (otherwise we'd break apart from the sheer amount of the input to process).

Oh, and the thumb trick isn't magic. It's about parallax and physiological diplopia.

//L

 

[Paultricounty]

You know, we don't believe what we see. That's not how it works. The opposite is true, though - we see what we believe. But I have a very effective and simple method to challenge both the first group and the second group (those who admit to see what they believe).

I have two hands. On each hand I have a thumb, so my total number of thumbs is two, and two is the number of my thumbs.

But I can easily make nearly everybody admit that it looks that I have three thumbs, and not by sneaking in any other body part. They admit they see three thumbs.

The first group must, in order to be coherent and consequent, accept that I actually have three thumbs. Or else, abandon their paradigm that they believe what they see

The second group, who obviously neither believe I have three thumbs, must admit to see three thumbs without actually believing it.

It is all about what we choose to ignore. And we all ignore incredible amounts of visual information (otherwise we'd break apart from the sheer amount of the input to process).

Oh, and the thumb trick isn't magic. It's about parallax and physiological diplopia.

//L

😧🙃🥷🏼😵‍💫

 

[Binastro]

Yes, I have three thumbs also.

Regards,
B.

 

[henry link]

I've got four.

 

[Binocollector]

I can make it look like I'm ripping off my thumb and glue it back on with spit. Neat little magic trick for the next children's birthday party .

 

[Trinovid]

I was able to help a friend out with some dimensional lumber for a deck repair. Initially some of the 2x6 material looked like they might not be long enough but it turned out that they were 12' and 14' boards. Maybe using a tape measure would have sooner verified what we later found to be true.

I'm also assuming the sun has set, but at least I have a basis for this belief in that it has been dark outside for hours now. But, I'm still not completely sure that there might not be another reason for it. Hope I'm not delusional.

 

[Canip]

I'm also assuming the sun has set,….

Definitely not! The sun hasn‘t moved a bit (well, it has, as part of the rotation of the galaxy), it‘s the earth that has „set“ the sun 😂, unless … unless the earth is flat … 🤔

P.S. the above is not politics and not intended to be (I am a lawyer, so disclaimers are appropriate 🤣)

 

[Trinovid]

…unless the earth is flat … 🤔

Earth is definitely not flat (unless you have the proper depth of field), but, thankfully, my kitchen floor is.

 

[bsantini]

Anything in the optical train that increases contrast will increase the “apparentness” of edges, which will be visually interpreted as increases sharpness.

Barry

 

[Paultricounty]

Definitely not! The sun hasn‘t moved a bit (well, it has, as part of the rotation of the galaxy), it‘s the earth that has „set“ the sun 😂, unless … unless the earth is flat … 🤔

P.S. the above is not politics and not intended to be (I am a lawyer, so disclaimers are appropriate 🤣)

As a former legal scholar I believe what is and what is not politics is open for interpretation. For some people here , just the word politics (or MIC) induces panic 😵‍💫😧✌🏼🙏🏼. We’re you suggesting the earth is flat, you know there are a lot of people who believe that 🤭.

 

[Maljunulo]

This non-political statement is non-political.

 

[Paultricounty]

This non-political statement is non-political.

Lol, by who’s opinion 🙄

 

[Trinovid]

This non-political statement is non-political.

I can’t find even a single flaw!

 

[tenex]

This statement is non-political.
Nothing is non-political.
---------------------------------
This statement is nothing.