Depth of Field - I am confused (2 Viewers)

[Hermann]

How this optical property can be mesured for afocal optics?
The post implies the perceived DOF cannot be measured. It is so?

Read looksharp65's excellent posting again. Try to understand it. All the answers are there.

Hermann

 

[looksharp65]

How this optical property can be mesured for afocal optics?
The post implies the perceived DOF cannot be measured. It is so?

Ted and Maljunolo, your comments are excellent. Perceived DOF in an afocal instrument is by definition not possible to measure since it's constantly changing.
Using a camera like in digiscoping might, if all settings are correct, in theory, show resolution differences fore and aft the point of focus. But even if (theoretically) such differences were detected, and I can't see how they could exist, these differences in 'real' DOF should still be subject to the magnitudes higher differences in perceived DOF that would erase any possibility to detect them while using the instrument as intended.

Let me, at last, reiterate, the fact that 'real' or 'measurable' DOF of focal instruments, needs to be conditioned with visual acuity and image scale.
If either goes up, it will reveal that 'real' DOF is a chimera, an agreement resting upon the aforementioned conditions.
However, more practically, grain size or pixel size will determine the limit. If these were infinitesmally small, I guess the limit rather would be due to the wavelengths of light.
This was not sufficiently clear in my previous post. In reality, a print could show maximum resolution within a 'real DOF', limited only by grain or pixel size, which simply masks the fact that increased magnification and/or visual acuity would have revealed defocus.

//L

 

[Ted Y.]

In reality, a print could show maximum resolution within a 'real DOF', limited only by grain or pixel size, which simply masks the fact that increased magnification and/or visual acuity would have revealed defocus.

I want to determine the DOF for binoculars of same magnification, in same weather conditions, for my visual acuity, in same conditions of fatigue. I am not interested to compare with other people, other magnification, different view fatigue.
The measurement can reveal differences or not, it is affected by errors, relevant or not, etc.

It is a practical approach, just measurement. No formulas.

Do you say I can measure?
Do you tried and failed?
This is just your extrapolation based on science if I understand correctly.

 

[Paultricounty]

I posted this in an other discussion, I figured best to move it here.

I couldn’t get the link right so I’ll post a picture of my less than Scientific test back from September. This was done with four observers at a local coastguard station. Three observers were knowledgeable with optics, the fourth was just a drunk guy who wouldn’t go away , so we let him participate if he promised not to breath or sneeze on the glass 😧. All but the drunk agreed on the results, he didn’t even understand what we were talking about, even after each person explained to him what we were doing every time we looked through a different binocular. I will say he was very smitten with the Nikon E2, and if he had the chance I think he might’ve tried to run off with it.

 

[Ted Y.]

I posted this in an other discussion, I figured best to move it here.

I couldn’t get the link right so I’ll post a picture of my less than Scientific test back from September. This was done with four observers at a local coastguard station. Three observers were knowledgeable with optics, the fourth was just a drunk guy who wouldn’t go away , so we let him participate if he promised not to breath or sneeze on the glass 😧. All but the drunk agreed on the results, he didn’t even understand what we were talking about, even after each person explained to him what we were doing every time we looked through a different binocular. I will say he was very smitten with the Nikon E2, and if he had the chance I think he might’ve tried to run off with it.

I cannot disagree with you results. I can disagree with the method you used.

I used a rangefinder to measure the begin and end distances of DOF for a few 8x binoculars and I have found differences.
Also, I have found that a quick focus binocular has a very, very short zone of acceptable clarity and this give a lot more precise result (and also credible).

 

[Paultricounty]

I cannot disagree with you results. I can disagree with the method you used.

I used a rangefinder to measure the begin and end distances of DOF for a few 8x binoculars and I have found differences.
Also, I have found that a quick focus binocular has a very, very short zone of acceptable clarity and this give a lot more precise result (and also credible).

Hi Ted,

We talked about using a rangefinder as one guy had the Swaro TA’s but unfortunately didn’t have them that day. We also considered wanting to go the perceived route because we considered that each binocular had a slightly different edge that could effect what stays in focus. I also considered that even if measured that it would be such a slight amount of difference that it may not be perceived visually. We also need to consider the measurement in DOF is being effected by edge quality or lack thereof.

So in one hand it would appear that the majority or most emphasis for determining DOF with two like magnification binos would be the magnification. If we had more people we then could’ve had a larger test group with more deviation in eyesight, to see if that had an effect. But to ad a little more for thought is we considered the edge correction in each binocular, and decided we would try to disregard the last 10% or so of the edge , and see if the test results were the same, and they were.

Paul

 

[Paultricounty]

I cannot disagree with you results. I can disagree with the method you used.

I used a rangefinder to measure the begin and end distances of DOF for a few 8x binoculars and I have found differences.
Also, I have found that a quick focus binocular has a very, very short zone of acceptable clarity and this give a lot more precise result (and also credible).

I’m not sure I’m following you on fast focuser. Again we didn’t see any perceived difference wether the binoculars had a slow, medium or fast focuser. If the closest object was in focus with all the test binoculars then it was in focus. Again we could discuss edge degradation having an effect but focus speed didn’t seem to have any effect.

 

[henry link]

How this optical property can be mesured for afocal optics?
The post implies the perceived DOF cannot be measured. It is so? judge

Perceived DOF can be measured (or at least accurately observed) by using a simple technique.

First, abandon trying to judge how "fuzzy" extended objects appear to be in front or behind of a focused object. Instead, use a point source of light (an artificial star) for the focused target and identical point sources for the defocused objects placed in front and behind. That will produce a single easily observed circle of confusion in front and behind the focused object instead of many overlapping circles of confusion. What you're looking for is not a lack of sharpness, but the exact size of the diffraction discs formed by the defocussed point sources. The larger the diffraction discs the fuzzier an extended object at that distance would appear to be, but the size of a circle is far easier to judge than a gradual loss of sharpness and if the diffraction discs are large enough then everyone can judge their size differences accurately regardless of eyesight acuity.

I redid an experiment just now that demonstrates the surprising result that true defocus in a telescope or binocular (as determined by the number of diffraction rings that make up the image of a defocussed star rather than the size of the circle of confusion) doesn't change at all with magnification. What we see when we change from 6x to 12x is not more defocus of the objects in front and behind a focused object, but simply the very same defocus enlarged. All binoculars of the same magnification have the same DOF because the number of diffraction rings is always the same for the same distance from focus and the size of the circle of confusion formed by those rings is by definition being magnified by the same amount.

 

[Paultricounty]

Perceived DOF can be measured (or at least accurately observed) by using a simple technique.

First, abandon trying to judge how "fuzzy" extended objects appear to be in front or behind of a focused object. Instead, use a point source of light (an artificial star) for the focused target and identical point sources for the defocused objects placed in front and behind. That will produce a single easily observed circle of confusion in front and behind the focused object instead of many overlapping circles of confusion. What you're looking for is not a lack of sharpness, but the exact size of the diffraction discs formed by the defocussed point sources. The larger the diffraction discs the fuzzier an extended object at that distance would appear to be, but the size of a circle is far easier to judge than a gradual loss of sharpness and if the diffraction discs are large enough everyone can judge their size differences accurately regardless of eyesight acuity.

I redid an experiment just now that demonstrates the surprising result that true defocus in a telescope or binocular (as determined by the number of diffraction rings that make up the image of a defocussed star rather than the size of the circle of confusion) doesn't change at all with magnification. What we see when we change from 6x to 12x is not more defocus of the objects in front and behind a focused object, but simply the very same defocus enlarged. All binoculars of the same magnification have the same DOF because the number of diffraction rings as always the same for the same distance from focus and the size of the circle of confusion formed by those rings is by definition being magnified by the same amount.

Settled 🙏🏼

 

[William Lewis]

I do hope so.

If you value depth of field and stability get a low magnification, if you don't mind a bit of shake and a shallow depth of field get a higher magnification and if you want a high magnification and stability get an i.s model.

 

[tenex]

Henry has a good point as to the difficulty of trying to quantify fuzziness, but like every valid point in all the threads about DOF, it ultimately goes nowhere because people just keep misusing the term itself. When I, knowing what "DOF" means as an optical term, fail to detect a difference between any binoculars of the same magnification that I've ever compared, there's no real need to resort to more precise techniques of measurement to see what I've missed; this is the expected result, and nothing remains to be explained. When others, apparently not knowing what "DOF" means, confidently state that one such model has dramatically more than another, we can be quite sure that they aren't merely being a bit sloppy in judging fuzziness, so more precise techniques won't help. They aren't trying to judge DOF at all, but considering something else and misappropriating the term.

Most likely they're evaluating an entire field that shows more or less curvature affecting what seems sharp, but recently we've also seen that something as simple as a slower focuser can give the impression of "less DOF" due to more focusing effort, which isn't even an optical effect at all, just faulty reasoning. Two related errors keep occurring: misunderstanding the precise definition of DOF, and failing to distinguish it from other effects. Sanity does indeed become an issue, because after having the relevant points explained yet again, the majority of posters just keep on saying the same thing. I don't think there's anything particularly murky or complicated or mysterious about this, and know of no cure. "When I use a word," Humpty Dumpty said in rather a scornful tone, "it means just what I choose it to mean -- neither more nor less."

 

[Ted Y.]

Perceived DOF can be measured (or at least accurately observed) by using a simple technique.

How is your method equivalent to DOF measurement?
Please post a technical reference for this relation. Not a opinion. Not a forum. Thank you.

 

[Paultricounty]

I’d say that some of the confusion on this , at least it was for me a while back, is that some of the so called and popular expert reviewers ( don’t want to mention names to offend) have stated in there reviews that this or that binocular had more DOF than a previous model of the same magnification or some other brands same magnification was super or inferior in DOF. I also don’t want mention names because I like some of those people 😔.

But I think quite a few here know some of whom I’m talking about.

Paul

 

[Ted Y.]

I would say that some of the confusion on this is that some of the so called and popular expert reviewers (don’t want to mention names to offend) have stated in their reviews that DOF depends only on magnification without technical references. Just very strong opinions. I also do not want mention names because I like some of those people.

Probably a few here know some of whom I’m talking about.

This is a sincere adaptation of the previous post. It seems we agree to disagree.

 

[Canip]

All binoculars of the same magnification have the same DOF

Ted (post # 94), are you saying that Henry is wrong?

 

[looksharp65]

Perceived DOF can be measured (or at least accurately observed) by using a simple technique.

First, abandon trying to judge how "fuzzy" extended objects appear to be in front or behind of a focused object. Instead, use a point source of light (an artificial star) for the focused target and identical point sources for the defocused objects placed in front and behind. That will produce a single easily observed circle of confusion in front and behind the focused object instead of many overlapping circles of confusion. What you're looking for is not a lack of sharpness, but the exact size of the diffraction discs formed by the defocussed point sources. The larger the diffraction discs the fuzzier an extended object at that distance would appear to be, but the size of a circle is far easier to judge than a gradual loss of sharpness and if the diffraction discs are large enough then everyone can judge their size differences accurately regardless of eyesight acuity.

I redid an experiment just now that demonstrates the surprising result that true defocus in a telescope or binocular (as determined by the number of diffraction rings that make up the image of a defocussed star rather than the size of the circle of confusion) doesn't change at all with magnification. What we see when we change from 6x to 12x is not more defocus of the objects in front and behind a focused object, but simply the very same defocus enlarged. All binoculars of the same magnification have the same DOF because the number of diffraction rings is always the same for the same distance from focus and the size of the circle of confusion formed by those rings is by definition being magnified by the same amount.

Henry, I agree this is a simple method to again prove the truth that DOF varies with magnification. The method we both dismiss, to visually try to judge fuzziness, is out of the question due to its total lack of reliability and repeatability. But I think it isn't quite correct to call your method 'measurement of perceived DOF'.
Your method is simple but also technical to its nature, but is very different to ordinary binocular usage and the DOF experience so often referred to.
People refer to what seems sharp.

The technical nature of the method ends with the use of an eye and the subjective assessment of disc sizes, which here becomes the perceptual part of the method. My objection is that assessment of size not necessarily is equally straightforward for everyone. I myself am notoriously bad at judging sizes of birds, and sometimes I fail with a factor of 2. Furthermore, to my eyes the Nikon E II 8x30 has a greater magnification than any of my 8x roofs.
If anything, the porro effect should be the opposite to what my eyes tell me.

So unless it's a reticle binocular, I wouldn't trust my own eyes to assess the size of diffraction discs. But if the final step, the one I don't wholly agree qualifies as 'perceived', was omitted and replaced by a camera, then I'd say it is a useful demonstration of real DOF (or rather lack thereof)

//L

 

[Ted Y.]

Ted (post # 94), are you saying that Henry is wrong?

Nope. I have no reasons for this.
When I do not know, I ask questions.
Henry can answer or not, I will search my self on Internet.

Not about Henry, not about Canip:
I do not know who is right about DOF. Maybe each of us.
I know I measured and it is different for same 8x magnification. Opinions or strong opinions cannot beat this. Nor the attitude.

 

[Hermann]

I would say that some of the confusion on this is that some of the so called and popular expert reviewers (don’t want to mention names to offend) have stated in their reviews that DOF depends only on magnification without technical references. Just very strong opinions.

König, Albert & Horst Köhler: Die Ferngläser und Entfernungsmesser. 3rd edition, 1959. Berlin, Heidelberg: Springer, p.122-125.

Hermann

 

[Paultricounty]

I would say that some of the confusion on this is that some of the so called and popular expert reviewers (don’t want to mention names to offend) have stated in their reviews that DOF depends only on magnification without technical references. Just very strong opinions. I also do not want mention names because I like some of those people.

Those are the ones I agree with because it’s the same result we got with four people, including the one drunk. I wouldn’t think it would offend the reviewers, considering they’re accurate 🤪✌. I think you’ll come around once you read up a bit 🙏🏼

Probably a few here know some of whom I’m talking about.

This is a sincere adaptation of the previous post. It seems we agree to disagree.

 

[Ted Y.]

Those are the ones I agree with because it’s the same result we got with four people

I do not contest the results and I do not find something offensive in your post.

I am out of this thread.