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depth of field (1 Viewer)
- Thread starter lmans66
- Start date
henry link
Well-known member
Well, there is a specification. It's called magnification; the lower the magnification of an afocal device like a telescope or binocular the wider the DOF. The only exception to that rule is when the exit pupil of the telescope is smaller than the pupil size of the eye, which has the effect of increasing the DOF of the eye.
You'll find plenty of subjective impressions reported here that suggest there are differences in DOF among binoculars with the same magnification. There are reasons for those impressions and some of them could be specified. Fast focus speed, for instance, creates for some an impression of shallow DOF and that could be specified in diopters of focus change per degree of focuser rotation. A large amount of field curvature can create an impression of wide DOF since close objects near the edge of the field are simultaneously in focus with distant objects at the field center. That could be specified in diopters of focus change per degree of apparent field away from the center.
You'll find plenty of subjective impressions reported here that suggest there are differences in DOF among binoculars with the same magnification. There are reasons for those impressions and some of them could be specified. Fast focus speed, for instance, creates for some an impression of shallow DOF and that could be specified in diopters of focus change per degree of focuser rotation. A large amount of field curvature can create an impression of wide DOF since close objects near the edge of the field are simultaneously in focus with distant objects at the field center. That could be specified in diopters of focus change per degree of apparent field away from the center.
I'd just add to Henry's comments and mention that light level alters our perceived depth of field (and visual acuity). In bright conditions when the pupil of the eye contracts the DOF appears greater than in lower light with wider pupils. Think of it like changing the f/number on a camera.
David
David
Thanks but that still doesn't really speak to what I am saying....if I can look in one pair of bino's such as a swaro and not have to continually play with the focus...I have a larger depth of field than a pair of binos' that does not show near by birds or objects in focus....
For instance...I was looking at a squirrel tail the other day thru a SLC....the detail was superb and with excellent depth of field. While another bino, while in perfect and crisp focus,...didn't show the depth of the tail, just the superficial or outer part...
Does that make sense? jim
For instance...I was looking at a squirrel tail the other day thru a SLC....the detail was superb and with excellent depth of field. While another bino, while in perfect and crisp focus,...didn't show the depth of the tail, just the superficial or outer part...
Does that make sense? jim
Taken from several sites 'googled'....Depth of Field:
Some binoculars, on the other hand, have such a narrow zone of acceptable focus that we are always straining to see through them, we are always fiddling with the focus ...
This parameter refers to the distance from "near to far" that is in focus at a certain setting of the focus adjustment or at a certain distance..... the depth of field can be so shallow that precise focusing is critical and so the location, size, action and feel of the focusing adjustment is an important consideration.
I have noticed that some binos such as the Swaro SLC have excellent depth of view while others (alpha as well as on down) have such shallow ones that one is constantly attempting to focus (or so it seems)....If depth of view has such an impact on the viewing, why are the specifications for depth of view not included as they do with FOV, as both equally have weight in determining a prime binocular?
Some binoculars, on the other hand, have such a narrow zone of acceptable focus that we are always straining to see through them, we are always fiddling with the focus ...
This parameter refers to the distance from "near to far" that is in focus at a certain setting of the focus adjustment or at a certain distance..... the depth of field can be so shallow that precise focusing is critical and so the location, size, action and feel of the focusing adjustment is an important consideration.
I have noticed that some binos such as the Swaro SLC have excellent depth of view while others (alpha as well as on down) have such shallow ones that one is constantly attempting to focus (or so it seems)....If depth of view has such an impact on the viewing, why are the specifications for depth of view not included as they do with FOV, as both equally have weight in determining a prime binocular?
brocknroller
porromaniac
I recently compared a sample black body 8x30 EII with my gray body 8x30 EII. The latter is an excellent specimen ("cherry" as they say), with a sweet spot nearly as big as the 8x32 SE entire FOV (~7* vs. SE's 7.5*) and gradually fall off at the edges after that. But that sweet spot does shrink a bit under abysmal lighting conditions.
The black body 8x EII has improved contrast like my 10x35 BB EII, but the depth perception isn't as good as the older gray body 8x EII.
The 8xEII BB sample has more field curvature (above and to the left like my 10x EII) than the older model, so according to what was written above that should give the impression of greater depth, but it doesn't. I have to focus more often with the BB 8x EII under the same lighting conditions compared with the GB 8x EII.
So as I've learned long ago, trying to apply logic to depth perception is futile. Logic is a little tweeting bird, chirping in a meadow. Logic is a wreath of pretty flowers which smell bad. Logic is... well, you get the idea.
<B>
The black body 8x EII has improved contrast like my 10x35 BB EII, but the depth perception isn't as good as the older gray body 8x EII.
The 8xEII BB sample has more field curvature (above and to the left like my 10x EII) than the older model, so according to what was written above that should give the impression of greater depth, but it doesn't. I have to focus more often with the BB 8x EII under the same lighting conditions compared with the GB 8x EII.
So as I've learned long ago, trying to apply logic to depth perception is futile. Logic is a little tweeting bird, chirping in a meadow. Logic is a wreath of pretty flowers which smell bad. Logic is... well, you get the idea.
<B>
james holdsworth
Consulting Biologist
henry link
Well-known member
Brock, one subject at a time, please. Depth of field and depth perception are two different things.
Imans,
DOF in binoculars has been thrashed out many times here over the years. If you search the subject you'll find plenty to read. I'm afraid there is lots of misinformation on the subject to found on the internet. I think the trick to coming to an understanding of DOF in binoculars is to first isolate it from other characteristics that mimic it.
That can be done with a simple test. First, don't try to judge the sharpness or lack of focus of an extended object. Instead, set up a glitter point in sunlight (any small shiny round object) about 20 feet away. Using only one eye focus on a distant object in the center of the field, then move the glitter point to the center of the field. The size of the diffraction disk formed by the defocused glitter point is determined entirely by how far out of focus it is. Compare the disk size to other binoculars of the same and different magnifications. In binoculars with a larger disk there is less DOF, if the disk is smaller there's more DOF. This filters out the effects of field curvature, focus speed, sample variations in axial aberrations and defects, etc., leaving only the DOF of the instruments as the one variable.
Henry
Imans,
DOF in binoculars has been thrashed out many times here over the years. If you search the subject you'll find plenty to read. I'm afraid there is lots of misinformation on the subject to found on the internet. I think the trick to coming to an understanding of DOF in binoculars is to first isolate it from other characteristics that mimic it.
That can be done with a simple test. First, don't try to judge the sharpness or lack of focus of an extended object. Instead, set up a glitter point in sunlight (any small shiny round object) about 20 feet away. Using only one eye focus on a distant object in the center of the field, then move the glitter point to the center of the field. The size of the diffraction disk formed by the defocused glitter point is determined entirely by how far out of focus it is. Compare the disk size to other binoculars of the same and different magnifications. In binoculars with a larger disk there is less DOF, if the disk is smaller there's more DOF. This filters out the effects of field curvature, focus speed, sample variations in axial aberrations and defects, etc., leaving only the DOF of the instruments as the one variable.
Henry
Interesting Henry.....I will try...thanks....might have to wait a day before I see sun though...
Regardless..... of the reason, some binoculars have that feeling of more 'infocus' while others are more 'hunting for the perfect focus'....
For Alphas....that should not be...all should be near the same since the product (focus without always having to hunt for it) should be an industry standard with Alphas....
Regardless..... of the reason, some binoculars have that feeling of more 'infocus' while others are more 'hunting for the perfect focus'....
For Alphas....that should not be...all should be near the same since the product (focus without always having to hunt for it) should be an industry standard with Alphas....
brocknroller
porromaniac
From lmans' post #4 and #10, it seems that depth perception is the subject, but I don't think he realized that in the OP. Hence, my post about it.
<B
Brock, Imans,
Just concentrating on the centre DOF rather than the effect of the periphery. If I need to hunt for focus in good light then I've always identified that it is resolution that is the problem. In such cases I don't usually get as far as checking DOF, but I'm happy to concede it would appear shorter in such cases.
David
Just concentrating on the centre DOF rather than the effect of the periphery. If I need to hunt for focus in good light then I've always identified that it is resolution that is the problem. In such cases I don't usually get as far as checking DOF, but I'm happy to concede it would appear shorter in such cases.
David
I believe that magnification would influence the size of the out of focus glitter point, just as with the the case in astronomical scopes of examining the diffraction pattern. Although it results from other effects, the diffraction pattern also results from a failure to focus. Its apparent size scales with magnification.
This provides us with another way of understanding why higher magnifications come with worse (smaller, shallower) depth of field. It is consistent with a thought that I have had, that the worse DOF with higher magnifications results simply from being able to see focusing errors more clearly.
Is this correct? What do you think, Henry?
Ron
This provides us with another way of understanding why higher magnifications come with worse (smaller, shallower) depth of field. It is consistent with a thought that I have had, that the worse DOF with higher magnifications results simply from being able to see focusing errors more clearly.
Is this correct? What do you think, Henry?
Ron
henry link
Well-known member
Hi Ron,
I tried to cook up a test to see if the defocused diffraction pattern is simply enlarged by higher magnification or if a higher magnification disk is also comprised of more diffraction rings, indicating greater defocus.
I boosted the magnification of my 8-16x40 Nikon zoom binocular by 3x to see the rings better. Focusing on the same object and using the same defocused glitter point the diffraction disk formed at 48x is much larger than the 24x disk and there are also about twice as many rings at 48x than at 24x. That appears to indicate that the 48x disk is not just a magnified version of 24x but also genuinely more defocused. What do you think?
Henry
I tried to cook up a test to see if the defocused diffraction pattern is simply enlarged by higher magnification or if a higher magnification disk is also comprised of more diffraction rings, indicating greater defocus.
I boosted the magnification of my 8-16x40 Nikon zoom binocular by 3x to see the rings better. Focusing on the same object and using the same defocused glitter point the diffraction disk formed at 48x is much larger than the 24x disk and there are also about twice as many rings at 48x than at 24x. That appears to indicate that the 48x disk is not just a magnified version of 24x but also genuinely more defocused. What do you think?
Henry
regarding the depth of field.
One of the problems seems to be that the in focus star images vary very greatly.
With the same specification binoculars some have very bloated in focus star images and some, the minority, have tiny point images.
This has many effects.
Firstly, fainter stars can be seen with the binocular with tiny style images.
Secondly, the resolution of double stars is much better when the star images are tiny.
Of course this is all influenced by the size of the observers pupils in comparison with the binocular exit pupils.
So when you defocus the star images you are already starting from different initial sizes of the in focus star images.
When I see mention of depth of field in regards to birdwatching binoculars I am afraid I just switch off.
To me as an astronomer it is similar to when people ask me whether I am an astrologer.
It amazes me that perhaps 50% of the population believe in astrology and the purveyors of this by so-called astrologers just astonishes me.
But what can I do about this. Reason and rationality don't come into it.
So if birdwatchers feel that certain binoculars have greater depth of field then it is up to them to use these binoculars if they wish to.
I know that my 6 x 18 yellow waterproof seven-day shop binoculars that cost 7 pounds and has individual eyepiece focusing do have varying focus across the field.
I focus the centre on Infinity and if I want to look at something close up I just tilt the binocular bit up and use the bottom of the field.
Then close objects are in focus because the field is curved.
And I can use intermediate positions also, so I never have to refocus.
The whole topic of depth of field is of course compounded by the Observer and the eye brain perceptions and I don't think scientific analysis can really be expected to come to definite conclusions.
One of the problems seems to be that the in focus star images vary very greatly.
With the same specification binoculars some have very bloated in focus star images and some, the minority, have tiny point images.
This has many effects.
Firstly, fainter stars can be seen with the binocular with tiny style images.
Secondly, the resolution of double stars is much better when the star images are tiny.
Of course this is all influenced by the size of the observers pupils in comparison with the binocular exit pupils.
So when you defocus the star images you are already starting from different initial sizes of the in focus star images.
When I see mention of depth of field in regards to birdwatching binoculars I am afraid I just switch off.
To me as an astronomer it is similar to when people ask me whether I am an astrologer.
It amazes me that perhaps 50% of the population believe in astrology and the purveyors of this by so-called astrologers just astonishes me.
But what can I do about this. Reason and rationality don't come into it.
So if birdwatchers feel that certain binoculars have greater depth of field then it is up to them to use these binoculars if they wish to.
I know that my 6 x 18 yellow waterproof seven-day shop binoculars that cost 7 pounds and has individual eyepiece focusing do have varying focus across the field.
I focus the centre on Infinity and if I want to look at something close up I just tilt the binocular bit up and use the bottom of the field.
Then close objects are in focus because the field is curved.
And I can use intermediate positions also, so I never have to refocus.
The whole topic of depth of field is of course compounded by the Observer and the eye brain perceptions and I don't think scientific analysis can really be expected to come to definite conclusions.
brocknroller
porromaniac
Binastro,
I think 50% might be too high a figure, but then, I live in a college town, so our population isn't representative of the rural towns surrounding us where the confusion about astronomy vs. astrology might be more prevalent.
I did have a neighbor who lived nearby in her parents' condo but who was born on a farm, and she saw my telescope and asked if I were an astrologer. I said, "No, I'm a palm reader, let me see your hand." :smoke:
Part of the confusion might go back to ancient times when astronomers were astrologers (they had to make a living, and their rich patrons wanted ROI than just basic science
. "For 1500 years, the astronomy of Ptolemy and the cosmology of Aristotle held together a scientific world view, one that was inclusive of astrology. These two thinkers from the ancient world had described nature in such a way that the astrological influence of the stars and planets was absolutely logical. Ptolemy's earth-centered model of the solar system, as bizarre as it seems to us today, worked well enough to be used to create ephemerides of the planets. Ptolemy also wrote "the book" on astrology, his Tetrabiblos. Aristotle's layered heavens, in which the higher levels of the planets could influence the earth at the center, were an obvious rationale for astrology."
and
"Denmark produced one of the greatest astronomer/astrologers that ever lived, Tycho Brahe. Brahe got an early start in the starry sciences and was reading Ptolemy by age 14. At 17, he was making his own astronomical observations and found that the ephemerides of his day, the Alphonsine Tables, were off by a month in regard to Jupiter and Saturn. He apparently was interested in astrology because he kept a book of his friends' horoscopes during his early years."
http://www.mountainastrologer.com/standards/editor%27s%20choice/articles/science_ast.html
With a penumbral lunar eclipse on May 25, and last night's conjunction of Venus and Jupiter, and Neptune turning retrograde next week, I would say the planets align with your statement (and so do I).
Brock
. Well at least Brock you made me laugh.
Newton was into some strange stuff as well.
Tycho Brahe I think lost his nose.
I think that the above were a little bit argumentative as well.
For the last few days Mercury was also in it making a triple apparition and the photos of this are very nice. I think it's another 13 years may be to the next one.
I do think that the time of the year you were born makes a difference, for instance regarding allergies and your immune system etc. But that's about it.
In the 1970s I was very interested in space colonisation as envisaged by Prof O'Neill in the USA. I actively supported his group.
I wrote several full-page or double page spreads in newspapers and magazines.
Unfortunately, this led some of those not very scientifically minded to believe I was recruiting members of the public to live in a space cities, which had maybe 100,000 inhabitants each. So I was well avoided. Mind you some hippy type girls took an interest in me. so it wasn't all bad publicity.
Now, I realise how crazy we were back then.
Even if we had these cities which relied on multiple shuttles, with hundreds of flights a year, electro magnetic slings on the moon that threw enormous amounts material to the L points in orbit.
I now think they would have been wars between the cities.
Humans are by nature not very peaceful and living in enormous space cities with rather thin shells would not have been very realistic.
They did have protection from radiation but a few anti-tank rounds would have not done them much good.
Anyway instead of having hundreds of thousands of people in space as envisaged by now we have perhaps less than 10 and cannot even afford those.
Oh the innocence of youth.
Newton was into some strange stuff as well.
Tycho Brahe I think lost his nose.
I think that the above were a little bit argumentative as well.
For the last few days Mercury was also in it making a triple apparition and the photos of this are very nice. I think it's another 13 years may be to the next one.
I do think that the time of the year you were born makes a difference, for instance regarding allergies and your immune system etc. But that's about it.
In the 1970s I was very interested in space colonisation as envisaged by Prof O'Neill in the USA. I actively supported his group.
I wrote several full-page or double page spreads in newspapers and magazines.
Unfortunately, this led some of those not very scientifically minded to believe I was recruiting members of the public to live in a space cities, which had maybe 100,000 inhabitants each. So I was well avoided. Mind you some hippy type girls took an interest in me. so it wasn't all bad publicity.
Now, I realise how crazy we were back then.
Even if we had these cities which relied on multiple shuttles, with hundreds of flights a year, electro magnetic slings on the moon that threw enormous amounts material to the L points in orbit.
I now think they would have been wars between the cities.
Humans are by nature not very peaceful and living in enormous space cities with rather thin shells would not have been very realistic.
They did have protection from radiation but a few anti-tank rounds would have not done them much good.
Anyway instead of having hundreds of thousands of people in space as envisaged by now we have perhaps less than 10 and cannot even afford those.
Oh the innocence of youth.
By the time the 19th Century rolled in even autodidact poets like William Blake had an understanding of the differences between science and astrology.
"The atoms of Democritus
And Newton's Particles of Light
Are sands upon the Red Sea shore
Where Israel's tents do shine so bright."
"The atoms of Democritus
And Newton's Particles of Light
Are sands upon the Red Sea shore
Where Israel's tents do shine so bright."
elkcub
Silicon Valley, California
Well, in the case of telescopes, the scientific community has come to definite conclusions. Because a telescope is an afocal system, the only meaningful use of the terms depth-of-focus or depth-of-field requires the instrument be used in conjunction with a human eye (or a focal system like a camera). In the case of most telescopes (binoculars) the two are analyzed as a single coupled optical system. The problem is not eye-brain perception, but being able to follow the instantaneous states of the eye's accommodation, pupil diameter, and retinal adaptation. Otherwise, the formulas are well worked out and not in dispute. Several approaches reach the same conclusions.
Unfortunately, the everyday use of the terms DOField or DOFocus doesn't exactly jibe with their technical meanings, and no one has yet come up with a practical demonstration of how it relates to, or differs from, binocular depth perception.
Ed
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brocknroller
porromaniac
