Depth of Field - I am confused (1 Viewer)

[jafritten]

I take it that DOF is mainly determined by magnification and effective exit pupil (e.g. a 6mm exit pupil may be stopped down to 3mm in daylight, the "effective" exit pupil would be 3mm). Thus, two sets of binoculars of the same dimensions (e.g. two 10x42s) should have the same depth of field. Now I find that some experienced users, reviewers and people well read in science (certainly better than I) talk about DOF in a way that I find confusing. Here are two quotes from Roger Vine (scopeviews), a reviewer well respected by many, including me:

"Depth of field is exceptional – focus on middle distance and you’re good for most birding without re-focusing." (Roger Vine on the NL Pure 8x42)
How can DOF be exceptional in a 8x42? Every 8x42 should have the same DOF, right? As far as I know, the NLs do not even have a curved field which could make the depth of field seem greater. Is it possible that focal length and a higher f/number play a role?

"Depth of field is good, but a touch less than the ELs’." (Roger Vine on the SLC 10x42)
Huh? Why is that?

As mathematical equations are usually well above my head, can anyone explain in plain English, please?

 

[Vespobuteo]

I take it that DOF is mainly determined by magnification and effective exit pupil (e.g. a 6mm exit pupil may be stopped down to 3mm in daylight, the "effective" exit pupil would be 3mm). Thus, two sets of binoculars of the same dimensions (e.g. two 10x42s) should have the same depth of field. Now I find that some experienced users, reviewers and people well read in science (certainly better than I) talk about DOF in a way that I find confusing. Here are two quotes from Roger Vine (scopeviews), a reviewer well respected by many, including me:

"Depth of field is exceptional – focus on middle distance and you’re good for most birding without re-focusing." (Roger Vine on the NL Pure 8x42)
How can DOF be exceptional in a 8x42? Every 8x42 should have the same DOF, right? As far as I know, the NLs do not even have a curved field which could make the depth of field seem greater. Is it possible that focal length and a higher f/number play a role?

"Depth of field is good, but a touch less than the ELs’." (Roger Vine on the SLC 10x42)
Huh? Why is that?

As mathematical equations are usually well above my head, can anyone explain in plain English, please?

Holger Merlitz' book "Handferngläser", 1st edition 2013:

p. 123: "The depth of field which an observer can attain is primarily determined by the accomodation capacity of his eyes, then also by the magnification of the binocular, and to a lesser degree by the diameter of the effective exit pupil..."

p. 30: "In internet forums there have been statements that the depth of field of a binocular can be affected or optimized by the optical design of the instrument. This is not the case... in the practice of observation, the illusion of an increased depth of field can be created by field curvature, because object near the observer which would not be sharp in the middle of the field of view appear still sharp in the lower part of the field ... this, however, is a side effect of an optical aberration and should not to be confused with real depth of field... the depth of field of an optical system scales with the reciprocal square of the magnification."

Depth of field, depth of focus: relevant to binoculars? - Binoculars - Cloudy Nights

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[Richard D]

One thing to note stated magnification of binoculars is an approximation - two different pairs of 8x42s could have different actual magnifications which will impact true depth of field.

Contrast as well as abberations can give the illusion of less/greater dof - it might not technically be dof but if you see an apparent difference...

 

[jafritten]

Holger Merlitz' book "Handferngläser", 1st edition 2013:

p. 123: "The depth of field which an observer can attain is primarily determined by the accomodation capacity of his eyes, then also by the magnification of the binocular, and to a lesser degree by the diameter of the effective exit pupil..."

p. 30: "In internet forums there have been statements that the depth of field of a binocular can be affected or optimized by the optical design of the instrument. This is not the case... in the practice of observation, the illusion of an increased depth of field can be created by field curvature, because object near the observer which would not be sharp in the middle of the field of view appear still sharp in the lower part of the field ... this, however, is a side effect of an optical aberration and should not to be confused with real depth of field... the depth of field of an optical system scales with the reciprocal square of the magnification."

Depth of field, depth of focus: relevant to binoculars? - Binoculars - Cloudy Nights

Page 1 of 2 - Depth of field, depth of focus: relevant to binoculars? - posted in Binoculars: Okay, I have a notion as to what they might mean in the binocular context, and a couple of examples, and would like conformation that I have it right. Depth of focus example: The 7x50 Nikon...

www.cloudynights.com

Vespobuteo, thank you for the quotes. These substantiate my view on DOF. They do not, however, explain Mr Vine's findings.

 

[Binastro]

In my opinion Mr Vine is wrong and Holger right.

Not only two 8x42s may have different magnifications, they may have different apertures, i.e. 42mm and 38mm.

In addition the observer may have eyes that have different prescriptions.
If the binocular is not fully adjusted to compensate for this difference, each eye focuses at a different distance.
The result is an increased DOF as the brain merges the two views.

I notice this when wearing simple correction glasses and otherwise no optical aid.
I have different prescriptions for each eye and I get a substantially increased DOF.
This is tiring in the long term, but for brief views very useful.

The main thing I notice with binoculars is the extra DOF provided by field curvature.

Regards,
B.

 

[Hermann]

Vespobuteo, thank you for the quotes. These substantiate my view on DOF. They do not, however, explain Mr Vine's findings.

Don't believe everything you read on the internet. Even a "well-respected reviewer" like Roger Vine may be wrong from time to time.

Hermann

 

[DuckNorris]

One thing to note stated magnification of binoculars is an approximation - two different pairs of 8x42s could have different actual magnifications which will impact true depth of field.

Contrast as well as abberations can give the illusion of less/greater dof - it might not technically be dof but if you see an apparent difference...

I have two 8x42's: a Celestron Nature DX and Nikon Monarch M7.

I printed the 1951 USAF resolution chart at 3x3" and viewed it from 50 ft away indoors under constant light with the bins on a tripod.

Both the Celestron and the Nikon could fully resolve the same line, but the Celestron came closer to resolving the next smaller line.

It did look to me that the Celestron had more magnification. The things on the chart seemed "bigger" with it.

The Nikon has a quoted 8.3 deg FOV, and the Celestron 7.4 deg.

I wounder if Nikon could be lowering the magnification a little below 8x to help boost the FOV spec?

Another thing I notice is the Nikon seems to have a little more stable handheld image than the Celestron. I think having lower magnification could explain that too.

 

[tenex]

In my opinion Mr Vine is wrong and Holger right.

Indeed, but this just begs the question, why doesn't Roger find that he has to refocus as much with NLs? (That may be a better way of putting it than talking about visual impressions of DOF.)

 

[Binastro]

I don't know.

I also have never looked through a full sized Swarovski except the old Habicht I have.

Regards,
B

 

[Maljunulo]

How does this reconcile with the relationship between F-Stop/F-Number and depth-of-field?

I think I also may need to be un-confused. (again)

 

[henry link]

How does this reconcile with the relationship between F-Stop/F-Number and depth-of-field?

I think I also may need to be un-confused. (again)

In an afocal device like a telescope there is no relationship between F-Stop/F-Number and depth-of field.

As long as the binocular's exit pupil is larger than your eye's entrance pupil the circle of confusion you see in front and behind a focused object is simply your eye's circle of confusion enlarged by the magnification factor of the binocular. A 10x binocular will magnify your eye's circle of confusion 25% more than an 8x binocular, so the 10x appears more defocused than the 8x simply because the eye's blur circle is 25% larger through the 10x than the 8x, even though the true defocus (indicated by the number of diffraction rings) is exactly the same for both.

The one and only case where the true defocus in front and behind a focused object can differ between two binoculars is when one of the binocular exit pupils is so small that it stops down the effective entrance pupil of the eye, thus increasing the eye's (not the binocular's) focal ratio, which reduces the the diameter of the eye's circle of confusion, and that does increase the eye's DOF, just like a camera lens.

Henry

 

[Maljunulo]

In an afocal device like a telescope there is no relationship between F-Stop/F-Number and depth-of field.

As long as the binocular's exit pupil is larger than your eye's entrance pupil the circle of confusion you see in front and behind a focused object is simply your eye's circle of confusion enlarged by the magnification factor of the binocular. A 10x binocular will magnify your eye's circle of confusion 25% more than an 8x binocular, so the 10x appears more defocused than the 8x simply because the eye's blur circle is 25% larger through the 10x than the 8x, even though the true defocus (indicated by the number of diffraction rings) is exactly the same for both.

The one and only case where the true defocus in front and behind a focused object can differ between two binoculars is when one of the binocular exit pupils is so small that it stops down the effective entrance pupil of the eye, thus increasing the eye's (not the binocular's) focal ratio, which reduces the the diameter of the eye's circle of confusion, and that does increase the eye's DOF, just like a camera lens.

Henry

Thank you Henry, and I’ll quit now while I still think I may understand it.

 

[WJC]

I take it that DOF is mainly determined by magnification and effective exit pupil (e.g. a 6mm exit pupil may be stopped down to 3mm in daylight, the "effective" exit pupil would be 3mm). Thus, two sets of binoculars of the same dimensions (e.g. two 10x42s) should have the same depth of field. Now I find that some experienced users, reviewers and people well read in science (certainly better than I) talk about DOF in a way that I find confusing. Here are two quotes from Roger Vine (scopeviews), a reviewer well respected by many, including me:

"Depth of field is exceptional – focus on middle distance and you’re good for most birding without re-focusing." (Roger Vine on the NL Pure 8x42)
How can DOF be exceptional in a 8x42? Every 8x42 should have the same DOF, right? As far as I know, the NLs do not even have a curved field which could make the depth of field seem greater. Is it possible that focal length and a higher f/number play a role?

"Depth of field is good, but a touch less than the ELs’." (Roger Vine on the SLC 10x42)
Huh? Why is that?

As mathematical equations are usually well above my head, can anyone explain in plain English, please?

"Depth of field is exceptional – focus on middle distance and you’re good for most birding without re-focusing."

This, of course, means you are leaving your BEST focus to the various accommodations of the various observers. This is why 100 percent of the "collimation tips" splattered all over the Internet are WRONG. Popularity does not validate opinion!

 

[jafritten]

Indeed, but this just begs the question, why doesn't Roger find that he has to refocus as much with NLs? (That may be a better way of putting it than talking about visual impressions of DOF.)

This is the very question that caused my confusion and made me open this thread.

In an afocal device like a telescope there is no relationship between F-Stop/F-Number and depth-of field.

As long as the binocular's exit pupil is larger than your eye's entrance pupil the circle of confusion you see in front and behind a focused object is simply your eye's circle of confusion enlarged by the magnification factor of the binocular. A 10x binocular will magnify your eye's circle of confusion 25% more than an 8x binocular, so the 10x appears more defocused than the 8x simply because the eye's blur circle is 25% larger through the 10x than the 8x, even though the true defocus (indicated by the number of diffraction rings) is exactly the same for both.

The one and only case where the true defocus in front and behind a focused object can differ between two binoculars is when one of the binocular exit pupils is so small that it stops down the effective entrance pupil of the eye, thus increasing the eye's (not the binocular's) focal ratio, which reduces the the diameter of the eye's circle of confusion, and that does increase the eye's DOF, just like a camera lens.

Henry

Thank you for your comprehensive explanation!

 

[Binocollector]

The one and only case where the true defocus in front and behind a focused object can differ between two binoculars is when one of the binocular exit pupils is so small that it stops down the effective entrance pupil of the eye, thus increasing the eye's (not the binocular's) focal ratio, which reduces the the diameter of the eye's circle of confusion, and that does increase the eye's DOF, just like a camera lens.

Thanks for the post. That was a very concise explanation. Should be made into a sticky at the top of the forum.
I have one question though - I've read lengthy discussions about this topic on a German astronomy forum and the explanation was similar. But I have a few questions - wouldn't a reduced entrance pupil of the eye increase perceived DoF? So a brighter bino (because of coatings, glass, etc) would seem to have more DoF than one that is more dim in case the eye's pupil would increase or decrease? (edit: on 2nd thought the bino would probably not increase brightness to decrease pupil size compared to not using a bino) And wouldn't therefore a larger FoV have a similar effect since it would deliver more light to the eye?

 

[Vespobuteo]

Vespobuteo, thank you for the quotes. These substantiate my view on DOF. They do not, however, explain Mr Vine's findings.

No they don't. The theoretical DOF and perceived DOF is obviously different things.
I wouldn't rule out his findings completely though, even though they are a bit "vague",
the guy have seen plenty more pairs of good binoculars than most people in this forum.

 

[Richard D]

No they don't. The theoretical DOF and perceived DOF is obviously different thing.
I wouldn't rule out his findings completely though, even though they are a bit "vague",
the guy have seen plenty more pairs of good binoculars than most people in this forum.

Agreed - contrast, resolution, brightness can all influence percieved depth of field even if they don't alter true depth of field.

 

[jeanluc125]

Hello

I have several pairs of binoculars, the DOP between my canon 10x30is and my Swarovsky NL Pure 10x32 does not seem very different.
On the other hand I found that my Zeiss Dialyt 8x30B have more DOP than my Swarovsky Habicht 8x30 (DV), difference between PORRO and ROOF ?
I also compared my Swarovsky Habicht 8x30 with my ZEISS Jena Detrintem 8x30, both PORRO type, without perceiving a significant difference ?
Comparing my Zeiss Dialyt 8x30B with my LEICA Ultravid 8X20, which are both ROOF, I don't see any real difference in DOP.
Hopefully I could contribute ....


Translated with DeepL

 

[Canip]

difference between PORRO and ROOF ?

No !

 

[Hermann]

No !

Seconded.

Hermann