orbitaljump
Well-known member
Nikon Monarch 8x36 vs Pentax 8x32 SP.
Thanks for your thoughts.
Thanks for your thoughts.
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Which binocular has better Depth of Field? (1 Viewer)
- Thread starter orbitaljump
- Start date
Took my 8x32 DCF SP out on the deck. Takes only a slight nudge to go from focused on a scrub pine in the back yard at ~25yds. to a house on a ridge over a mile away. About 1/4 turn to get back down to ~15ft. Another 1/4 turn to get down to half that(and very noticeable "binocular vision"), and another 1/4 gets the tops of my shoes, though it's best to close one eye at this point.
I assume this could vary based on your vision, so I don't know how it will do for a glasses wearer. There is very little adjustment left past infinity.
No idea about the 8x36 Monarch. Don't know that I've even seen one in person.
Based on past comparison to the 8x42 Monarch, the DCF SP should have better contrast and stray light or glare handling, along with higher quality construction.
Hope this helps.
I assume this could vary based on your vision, so I don't know how it will do for a glasses wearer. There is very little adjustment left past infinity.
No idea about the 8x36 Monarch. Don't know that I've even seen one in person.
Based on past comparison to the 8x42 Monarch, the DCF SP should have better contrast and stray light or glare handling, along with higher quality construction.
Hope this helps.
Depth of field is a measurable attribute of course. Unfortunately I don't have an 8x36 to compare to. However, I consider the 8x32 SP to have shallow depth of field, which is compared to my 7x35 porros which have incredible depth.
With camera systems, a larger aperture at a given magnification (f ratio) means shallower depth of field. All things equal, an 8x36 should have shallower dof than 8x32. However, there may be other factors and those may or may not be perceptable in practice.
Also, DOF is proportional to distance. Any binocular will have more depth of field at 50 meters than 10 meters. So for useful comparison, one with both binoculars should measure depth of field at a closer distance which will emphasize dof.
Bottom line, I like the SP way more than the Monarch for other reasons than dof so to me it is immaterial!
Matt
With camera systems, a larger aperture at a given magnification (f ratio) means shallower depth of field. All things equal, an 8x36 should have shallower dof than 8x32. However, there may be other factors and those may or may not be perceptable in practice.
Also, DOF is proportional to distance. Any binocular will have more depth of field at 50 meters than 10 meters. So for useful comparison, one with both binoculars should measure depth of field at a closer distance which will emphasize dof.
Bottom line, I like the SP way more than the Monarch for other reasons than dof so to me it is immaterial!
Matt
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Kevin Purcell
Well-known member
That's an rule of thumb for bins with the same physical size so a higher magnification use objective lens with a lower f/number and will have a lower DOF. The thread deals with that.
f/number of the objective is the causal issue.
Eyepiece design (or whole system design like including a field flattener can have a effect too ... reducing DOF).
DOF has a precise definition too: the range in the object domain whose images have a resolution that equals or exceed the detector.
Wikipedia has a decent if camera biased article
http://en.wikipedia.org/wiki/Depth_of_field
You can estimate it yourself by focusing on a close (5m?) object and viewing text (license plate or a sign) at some distance (40m or more). AB comparing bins this way easily reviews differences in DOF. Using text for the distant target (or a resolution target!) makes actually seeing the difference in DOF easier.
BTW to first approximation using the f/number argument (i.e. assuming the bins are the same length which I don't think they are!) the 8x36 would have a smaller DOF than the 8x32.
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orbitaljump
Well-known member
f/ratio
magnification
So the 36mm Monarchs have a faster f ratio being of nearly identical length to the 32mm Pentax but with a larger objective....and the same magnification?
magnification
So the 36mm Monarchs have a faster f ratio being of nearly identical length to the 32mm Pentax but with a larger objective....and the same magnification?
Kevin Purcell
Well-known member
Correct (except for the last bit which is redundant).
The magnification depends on the focal length and so does the f/number.
Of course this assumes no field flatters or other eyepiece (or internal focuser shenanigans). If bins were just simple astronomical telescopes it would be easier.
I find my SP 8x32 have perhaps a slightly smaller (but only fractionally) than the WP which has a less complex eyepiece. Both bins are the same length aside from EP length.
In real life for this sort of difference you have to try them out. Or rely on other peoples views. The difference won't be huge.
elkcub
Silicon Valley, California
Kevin, et. al,
Depth of field has been discussed in depth several times. |8|| I think the most recent thread is this one last May.
http://www.birdforum.net/showthread.php?t=114462
I attached a .pdf file on Post #7 in which I referred to Binocular DOF like the Emperor's new cloths. Everybody says they see it but it just ain't there. The paper has since been expanded and reviewed, but I'm reluctant to post it again because of BF's 24 hr. policy that makes it too difficult to modify later.
The camera and the eye are examples of focal systems. They focus an image on a receptor array, e.g., film or retina. Each has a defined depth-of-focus/field.
A telescope is an afocal system. It has no finite focal point, therefore, it also has no finite depth of focus. The focal lengths of the objective and eyepiece components make no difference when we are talking about the instrument as a whole.
When an afocal telescope is coupled to the eye, the only two properties that effect optical DOF are its magnification, m, and the exit pupil if it's smaller than the eye's pupil, i.e., EP < p. The smaller of the two defines the "effective" aperture of the combined system.
As seen in the paper, the DOF of a coupled eye-telescope system can be shown to be the DOF of the eye scaled by m. Hence, all telescopes with a given magnification and EP > p produce the same DOF. It doesn't matter what their component objective or eyepiece focal lengths happen to be.
My initial derivation of these relationships was based on the concept of "acceptable blur," as briefly developed in Warren J. Smith's, Modern Optical Engineering. Using additional references, it turns out the conclusion suffers no loss of generality at any working distance less than infinity. We have only to use m', which is the "effective" magnification of the telescope. As we all know, effective magnification increases as focusing distance decreases (but not linearly).
Using different theoretical starting points I've been told that others have found a scaling factor of m^2, but I haven't seen the math, just heard assertions. (See Mak's post #9.) The discrepancy may be because I'm missing something, like longitudinal vs. transverse magnification, or because the derivative of 1/m is -1/m^2. A plot of hyperfocal distance, for example, would appear to be quadratic in m. In any case, I don't think there is any dispute about effective magnification and exit pupil diameter being the only relevant variables.
We might keep in mind that DOF is a monocular property that refers to acceptable limits of axial defocus, i.e., blur. With a camera it's all very clear because the optics and film are static, and one can observe a print that is decoupled from the eye. It can not be evaluated accurately in a working telescope, however, due to constant accommodation and pupil changes of the eye, which vary the momentary focal length and aperture of the system. Hence, DOF for a telescope is really best determined theoretically, with an idealized instrument, static model eye, and working distance used as a parameter.
A second consideration is that there is great confusion between the concepts of depth of field/focus and depth/distance perception. Roll that together with your conjecture about flat-field effects on focusing, which I believe is valid, and we have a real Tower of Babble. An ideal flat field has the property of bringing all objects into focus that lie on a plane surface tangent to the circle (sphere) defined by the focusing radius. Nice if your looking at a star field, but not so nice if you move an off-axis object thirty feet away to the center, where it will have to be refocused. Most people don't realize that the field curvature of the eye's optics roughly matches the curvature (spherical cap) of the eyeball where the retina is located. Messing with this has consequences. So, I would agree, in general, that the field curvature will effect focusing—and one's depth illusion.
Ed
Depth of field has been discussed in depth several times. |8|| I think the most recent thread is this one last May.
http://www.birdforum.net/showthread.php?t=114462
I attached a .pdf file on Post #7 in which I referred to Binocular DOF like the Emperor's new cloths. Everybody says they see it but it just ain't there. The paper has since been expanded and reviewed, but I'm reluctant to post it again because of BF's 24 hr. policy that makes it too difficult to modify later.
The camera and the eye are examples of focal systems. They focus an image on a receptor array, e.g., film or retina. Each has a defined depth-of-focus/field.
A telescope is an afocal system. It has no finite focal point, therefore, it also has no finite depth of focus. The focal lengths of the objective and eyepiece components make no difference when we are talking about the instrument as a whole.
When an afocal telescope is coupled to the eye, the only two properties that effect optical DOF are its magnification, m, and the exit pupil if it's smaller than the eye's pupil, i.e., EP < p. The smaller of the two defines the "effective" aperture of the combined system.
As seen in the paper, the DOF of a coupled eye-telescope system can be shown to be the DOF of the eye scaled by m. Hence, all telescopes with a given magnification and EP > p produce the same DOF. It doesn't matter what their component objective or eyepiece focal lengths happen to be.
My initial derivation of these relationships was based on the concept of "acceptable blur," as briefly developed in Warren J. Smith's, Modern Optical Engineering. Using additional references, it turns out the conclusion suffers no loss of generality at any working distance less than infinity. We have only to use m', which is the "effective" magnification of the telescope. As we all know, effective magnification increases as focusing distance decreases (but not linearly).
Using different theoretical starting points I've been told that others have found a scaling factor of m^2, but I haven't seen the math, just heard assertions. (See Mak's post #9.) The discrepancy may be because I'm missing something, like longitudinal vs. transverse magnification, or because the derivative of 1/m is -1/m^2. A plot of hyperfocal distance, for example, would appear to be quadratic in m. In any case, I don't think there is any dispute about effective magnification and exit pupil diameter being the only relevant variables.
We might keep in mind that DOF is a monocular property that refers to acceptable limits of axial defocus, i.e., blur. With a camera it's all very clear because the optics and film are static, and one can observe a print that is decoupled from the eye. It can not be evaluated accurately in a working telescope, however, due to constant accommodation and pupil changes of the eye, which vary the momentary focal length and aperture of the system. Hence, DOF for a telescope is really best determined theoretically, with an idealized instrument, static model eye, and working distance used as a parameter.
A second consideration is that there is great confusion between the concepts of depth of field/focus and depth/distance perception. Roll that together with your conjecture about flat-field effects on focusing, which I believe is valid, and we have a real Tower of Babble. An ideal flat field has the property of bringing all objects into focus that lie on a plane surface tangent to the circle (sphere) defined by the focusing radius. Nice if your looking at a star field, but not so nice if you move an off-axis object thirty feet away to the center, where it will have to be refocused. Most people don't realize that the field curvature of the eye's optics roughly matches the curvature (spherical cap) of the eyeball where the retina is located. Messing with this has consequences. So, I would agree, in general, that the field curvature will effect focusing—and one's depth illusion.
Ed
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Tero
Retired
Ed, your example probably is OK in the ideal system. Our field observations may roll in curvature and sweet spot and depth of field together. Thus I had a Vortex and Bushnell 10x28 to try out and both were awful. The front of the bird was in focus, the back was not. My 10x42s do not do that.
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henry link
Well-known member
Ed,
Thanks for the excellent post and reference to your earlier PDF on the subject. I think you'll need to keep that handy. The illusion that DOF varies in binoculars of the same magnification can be very strong. To those who are still convinced that they see it, I can only suggest that some extra care be taken to separate true DOF from it's close imitators: focus speed, field curvature and differing aberration levels, both on and off axis.
Henry
Thanks for the excellent post and reference to your earlier PDF on the subject. I think you'll need to keep that handy. The illusion that DOF varies in binoculars of the same magnification can be very strong. To those who are still convinced that they see it, I can only suggest that some extra care be taken to separate true DOF from it's close imitators: focus speed, field curvature and differing aberration levels, both on and off axis.
Henry
Surveyor
The more I understand, the more I understand why I
As far as I have been able to estimate, the maximum depth of field occurs with no aberrations and is constant among binoculars with the same magnification if we limit the boundaries to the instrument itself, i.e. stop the comparisons at the exit pupil.
As Henry, Edz, Ed and others have pointed out, any aberration that increases the blur/distortion will act to limit the DOF (the COC or blur ratio reaches it’s limits faster).
As to the terms Depth of Field and Depth of Focus, my understanding of these terms is:
Depth of Field is the distance between the limits of the defined blur in object space (the actual field measurements).
The Depth of Focus may be regarded as the depth of field in image space. It gives the margin around the focal plane (i.e. exit pupil or the plane of exact focus, where the eye/film/detector is supposed to be) where the image blur is smaller than the prescribed blur diameter. Precisely half of the depth of focus is in front of the focal plane, and half of it in rear. See the attached calculated cross section of a focal point.
Best,
Ron
As Henry, Edz, Ed and others have pointed out, any aberration that increases the blur/distortion will act to limit the DOF (the COC or blur ratio reaches it’s limits faster).
As to the terms Depth of Field and Depth of Focus, my understanding of these terms is:
Depth of Field is the distance between the limits of the defined blur in object space (the actual field measurements).
The Depth of Focus may be regarded as the depth of field in image space. It gives the margin around the focal plane (i.e. exit pupil or the plane of exact focus, where the eye/film/detector is supposed to be) where the image blur is smaller than the prescribed blur diameter. Precisely half of the depth of focus is in front of the focal plane, and half of it in rear. See the attached calculated cross section of a focal point.
Best,
Ron
