Depth Of Field better when diameter is larger? (1 Viewer)

[Canip]

difference between PORRO and ROOF?

Nope! The laws of optics apply the same way as regards DOF.

 

[jeanluc125]

In theory certainly, but the purpose was to give a technical difference between the two binoculars, and it was the only one .... in any case a difference was noted between the two binoculars, both 8x30. I don't pretend to give the solution, just to leave a reasonable doubt at most.
Maybe it's the difference in optical formula between the two binoculars?

 

[Maljunulo]

Nope! The laws of optics apply the same way as regards DOF.

This.

The laws of optics are not suggestions, nor do they only work some of the time, or only on some instruments.

 

[Richard D]

 

[Binocollector]

Unfortunately the most in-depth explanation of the subject that I have read so far is only available in German and it is too much for me to quickly translate.

Richtigstellung: Schärfentiefe von Ferngläsern

Hallo Gemeinde, eigentlich bin ich derzeit so mit Problemlösungen für meinen neuen Macintosh G5 und dessen neues Betriebssystem OS 10.3 beschäftigt, daß ich mich hier gar nicht zu Wort melden dürfte (und deshalb auch seit fast drei Wochen nicht präsent war). Aber Franks Verweis im neuen...

forum-astronomie-de.translate.goog

 

[bsantini]

Regarding perceived depth of field:
It will depend upon (not necessarily in order)
The quality of optics in the binocular
The transverse optical correction of the objective
The difference in size between the observer’s pupil and the exit pupil
The difference, if any, between the plant of the exit pupil and the observer's entrance pupil
The position of the observer’s pupil within the exit pupil
The optical design of the eyepiece
The optical characteristics of the observer's eye
amongst other stuff.

At Televue, we tested both eyepieces, telescope objectives, barlows, and other optical accessories, using a custom 5" f/4 Pezval refractor with an integrated iris diaphram to see the effects across differing f/ratios and exit pupil situations. These were done using high precision ball bearings, which functioned effectively as a point source.




Discussion

 

[Hermann]

Unfortunately the most in-depth explanation of the subject that I have read so far is only available in German and it is too much for me to quickly translate.

Richtigstellung: Schärfentiefe von Ferngläsern

Hallo Gemeinde, eigentlich bin ich derzeit so mit Problemlösungen für meinen neuen Macintosh G5 und dessen neues Betriebssystem OS 10.3 beschäftigt, daß ich mich hier gar nicht zu Wort melden dürfte (und deshalb auch seit fast drei Wochen nicht präsent war). Aber Franks Verweis im neuen...

forum-astronomie-de.translate.goog

Yep. And for a more technical explanation cf. König, Albert & Horst Köhler (³1959) "Die Fernrohre und Entfernungsmesser", Berlin/Heidelberg: Springer, p. p.122-125. This stuff has been know for a long, long time.

Hermann

 

[tenex]

Unfortunately the most in-depth explanation of the subject that I have read so far is only available in German and it is too much for me to quickly translate.

Perhaps you could just explain the initial distinction he's trying to draw between Tiefenschärfe and Schärfentiefe... is it just wordplay?

Summary of post: magnification is simple geometry, it reduces DOF by increasing difficulty of accommodation, and qualities of particular binoculars of the same magnification do not affect DOF except very marginally where higher transmission or larger FOV causes the pupil to contract a bit further, or high spherical aberration creates difficulty judging DOF because the focal plane itself isn't truly sharp.

All of which is correct, but also shows the common tendency to disparage mistaken claims rather than merely correct them, and lack of interest in how some observers get a misimpression of differences in DOF. So once again I ask the OP, what did you see?

 

[Binastro]

I often bring the unfocussed bottom of a binocular field into play by using the curved field and edge vignetting.

This way I can easily read car number plates that are otherwise blurred.

This saves having to refocus.

As to the central field and actual DOF it depends also on the limitations of the observer's eyesight.
Acuity and accommodation probably play a part.

I suppose it is as complicated or as simple as one wants it to be.

Because my eyes have differing dioptre correction my cheap glass window shopping glasses of about plus 2 dioptres means my depth of field is vastly increased, but this approach becomes tiring, but is most useful for its purpose.

Regards,
B.

 

[Trinovid]

…the most in-depth explanation of the subject that I have read so far is only available in German and it is too much for me to quickly translate.

Are you likely to give us a brief summation or general overview in the next day or two?

 

[Binocollector]

Are you likely to give us a brief summation or general overview in the next day or two?

No. That's why I linked it to google translate.
Brief summary, apart from what we already have listed in the thread:
-- FoV plays a small role. Larger FoV, more light hits the eye, pupil constricts, slightly increased FoV
-- Lighttransmission: dito -- this might include shorter paths of the prisms, which also increases transmission, so construction of the instrument can play a small role
(The question I have however -- is that really noticeable at all?)
-- abberation of the eye-piece plays a role.

And something a member mentioned in the rest of the thread: field curvature can look as if the bino had a larger DoF, in case closer objects are also closer to the edge of the FoV so field curvature of the bino renders them sharp not the DoF.
Apart from that: two binos with same specs have same DoF.

 

[henry link]

Really, only the true magnification of two binoculars has to be the same for the DOF to be the same (as always, provided the exit pupils of both are larger than the eye's pupil, by any amount.) Of course, the magnification spec may be off. I measured the Swarovski 8x42 NL magnification as 8.23x and the 8x30 Habicht Porro as 7.8x, so those two "8x" binoculars would show a small difference in DOF.

I would add that 20 years ago I was one of those who didn't understand at all how DOF works in afocal telescopes and required considerable convincing by several members at Cloudynights and here, who knew better. I was really only fully brought on board when I finally convinced myself that only magnification mattered by use of the circle of confusion size test I mentioned earlier.

 

[Hermann]

This topic comes up every couple of years. There are several threads on this topic, and they all come to the same conclusion. As it should be, since everything one needs to know has been known for many, many years. Here's a sample of the threads, all easily found with the forum search:

Is binocular depth of field in focus variable?

I was comparing two different 10 x 42 binoculars today and there seemed, to my eyes, to be a slight difference in the depth of field in focus between the two in so far as more depth of the image seemed the be crisper between one make and the other. Is that possible if both are a 10 x 42? And if...

www.birdforum.net

Depth of field

Hi, I'm wondering what factors affect to the depth of field on spotting scopes (or binoculars also). It's clear that magnification is one of them but is it the only one? Does aperture or focal ratio have any effect? Are there some optical aberrations or defects (miscollimation?) that can...

www.birdforum.net

depth of field

Are there specifications in regards to Depth of Field that anyone has seen for binoculars? Swaro vs Zeiss vs Leika vs Nikon etc....?

www.birdforum.net

DOF = binocular & human

A new thread for discussing about DOF and freeing this one. Some older posts exist: here, here, here. It is no clear if the DOF depends only on the magnification of the binocular or on other factors, human eye included.

www.birdforum.net

Depth of Field - I am confused

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...

www.birdforum.net

Depth of field and f-stop of scopes

Hello, if I look at a camera lens, it has a f-stop value (which corresponds to the largest aperture, since the lens has a diaphragm that can make the aperture smaller). A fast aperture lets a lot of light in but has a shallow depth of field (thing are out of focus if they are even slightly off...

www.birdforum.net

Hermann

 

[Trinovid]

Brief summary, apart from what we already have listed in the thread:
-- FoV plays a small role. Larger FoV, more light hits the eye, pupil constricts, slightly increased FoV

And something a member mentioned in the rest of the thread: field curvature can look as if the bino had a larger DoF, in case closer objects are also closer to the edge of the FoV so field curvature of the bino renders them sharp not the DoF.

These two points you listed here are really helpful and also help in understanding not only how to address others misunderstandings as to the physics involved, but also equal misunderstandings by some trying to chase and correct others.
Thanks for taking the time to address these harder to understand additional details.

…the true magnification of two binoculars has to be the same for the DOF to be the same…provided the exit pupil of both is larger than the eye's pupil by any amount.

This too is another interesting observation, not only on the exit pupil equation, but also the uncertainty of exacting accuracy in labeling a particular model with an easily digested magnification spec.

These are, at least for me, the two most helpful posts in the entire thread so far, and so I say thanks to both of you very much!

 

[ReinierB]

Perhaps it's time to return to the original question. There is no theoretical reason why this would be the case, so we should ask how exactly you're judging DOF. Can you describe a certain scene observed with both, what you've focused on, which other elements seem sharp or don't, how far they are, etc? (Bear in mind that other factors may be involved too, for example field curvature reducing the area of best sharpness, so try to line elements up and do your DOF comparisons fairly close to the center.)

I haven't had time for it yet. But I will do that! I really thought the DOF is way better in the SLC 8x42, but maybe it only seemed better for whatever the reason. I will investigate that. After reading all your comments, it could not be true that the DOF is better in the 8x42. On the contrary, the DOF of the 8x25 should appear better because of the smaller true EP in darker conditions (in case my own pupil is bigger than 3.1 mm).

it should not affect the OP's comparison of an 8x25 and 8x42 at all

What do you mean with OP? You have written that before.

Interesting stuff. I am sorry I restarted this discussion/topic. I was not aware there are already a lot of threads about this topic.

You all left me puzzled, because I see what I see. Now I doubt what I saw. Let's see again, but now with the knowledge I have after reading your comments.
I will let you know.

 

[Binocollector]

What do you mean with OP? You have written that before.

"Original post" or "original poster". The person, who started the thread -- so in this case, you .

 

[ReinierB]

Thanks! Never too old to learn.

 

[Jim D.]

"I have a Swaro SLC 8x42 and a Zeiss Terra 8x25 and found the DOF of the 8x42 way better" doesn't suggest to me that the OP conducted laboratory measurements. Unless he was oddly curious about a very obscure technicality regarding optics, I imagine that he was concerned with the depth of field his eyes were perceiving.

 

[Binocollector]

Maybe the effect was caused by the larger FoV of the SLC -- 7.8° vs. 6.8°. Does the SLC have field flatteners? If not then in a larger FoV, curvature might be more prominent towards the edge, hence objects closer to the observer (which are also often closer to the edge of the FoV) might look in focus, suggesting a larger DoF that's not really there. Pure speculation on my part as I have never looked through either instrument.

 

[tenex]

Maybe the effect was caused by the larger FoV of the SLC -- 7.8° vs. 6.8°.

Thanks for pointing that out, I have no experience with Terra. Now we're back to the question, how much further can this really cause the pupil to contract?

Does the SLC have field flatteners? If not then in a larger FoV, curvature might be more prominent towards the edge, hence objects closer to the observer (which are also often closer to the edge of the FoV) might look in focus, suggesting a larger DoF that's not really there. Pure speculation on my part as I have never looked through either instrument.

No, neither is a flat-field design, which is why I brought up field curvature as a likely factor before. I've always supposed it has to be the primary explanation for claims like this. (Although offhand I'd expect SLC to have less than Terra...)

Interesting stuff. I am sorry I restarted this discussion/topic. I was not aware there are already a lot of threads about this topic.

You all left me puzzled, because I see what I see. Now I doubt what I saw.

No, don't apologize, investigate! The reason this topic just keeps coming up is that people never clarify what they've actually seen, and how they're (mis?)interpreting it as "DOF". If you can do that now, you'll confirm an explanation that we can offer with some confidence in the future. Which of these two has the larger zone of central sharpness, and does there still seem to be a difference in DOF within it?