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New Horizons II (1 Viewer)

Binastro

Well-known member
I have a Zeiss 5x10 monocular, which I think has relay lenses.

It has ridiculously long eye relief.

I don't have experience of rifle scopes.
Not sure if I have had one or not.

I have several Broadhurst Clarkson drawtube scopes that use relay lenses. Eye relief is not long.
Also perhaps a good Mirador scope. 30x75?

B.

P.S.
Simple eyepieces have eye reliefs of 0.3x focal length.

Plossls and Orthoscopics 0.8x focal length.

So values exceeding 1x may be modifications, or use different glass types or separations.
 
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Binastro

Well-known member
Although in a simple system of objective and eyepiece, I think that the eye relief is a function of the eyepiece.

If a Barlow is inserted, then the magnification can change radically depending on the position of the Barlow, and the eye relief also can change.

There is no problem with my 25x-135x80 binocular.
If the Barlow or other elements providing zoom were placed more critically, I see no reason why the top magnification could not be 250x or higher, but the image would become unstable and unusable eventually at even higher magnifications.

I don't know how far the eye relief could extend, but this may not depend only on magnification.
I suppose the eye relief could be extended to one foot or one metre if one played around with spacings and lenses.

With zoom lenses 30x has been around for a very long time.
Consumer cameras reach 83x optical zoom.
I think some lenses go much higher.

B,
 

Binastro

Well-known member
A Barlow lens should not affect the eye relief of the eyepiece if all elements are thin.

Cheap Barlows are single element, then achromatic Barlows are two elements.
Better ones are 3 element.
As the Power goes up they need to be more sophisticated.
The Powermates are 4 element, and say they restore rays to the original direction.
I think that they are up to 5x.

So to move the image and affect eye relief, I think that more than a simple Barlow is needed.

Camera teleconverters, which do a similar job are usually 4 element, but some are seven element.

Some converters, say from Minolta MD to Minolta AF, contain a lens and are about 1.2x or 1.25x and usually are 2 elements. They do move the image to increase back focus.

B.
 

Binastro

Well-known member
LER eyepieces.

I found a cutaway drawing of a 6 element long eye relief eyepiece.

It has a pair of very small field lenses at the front.
3 large lens elements in the middle and a very large eye lens at the back.
It is maybe a 2.5mm or 3.5mm focal length.

But I have not found a ray trace diagram.

The eye relief of these eyepieces is a constant 20mm throughout the focal length range.

Televue Delos and Pentax XW are examples of these LER eyepieces.

Can someone explain the principle behind these very short focal length eyepieces with 20mm eye relief?

Classic eyepieces have eye reliefs less than their focal length, but LER eyepieces can have eye reliefs 6x or 8x their focal length.

Regards,
B.
 

Binastro

Well-known member
LER eyepieces.

The secret is to have a negative field lens near, at or even before the focal point of the objective.
There is no pupil size and no aberrations.
A very concave front surface of the field lens achieves the long eye relief.

Positive field lenses are problematic.

Classic eyepieces were made for astronomy for simplicity as there were no antireflection coatings when single, double and three element eyepieces were designed.

There is an important paper by Dennis Taylor about 1918 that describes basically the Nagler design. It has rather many elements and chemical antireflection coatings were quite successful at this time.
It was anastigmatic and not designed for long eye relief, but that is one of the results.

I hope I got this right.

B.
 

Binastro

Well-known member
H. Dennis Taylor Anastigmatic long eye relief eyepiece.

Transactions of the Optical Society, vol 22, pp63-74.
A new Anastigmat flat field telescope and its application to Prismatic Binoculars.
H. Dennis Taylor.
Read and discussed 13 January 1921.

Left to right.

A small diameter quadruplet component. (He tried to use a cemented triplet but the curves were too violent).
A field stop?
A large meniscus field lens with concave surfaces to the left producing almost parallel rays.

A cemented triplet.
Then a close cemented doublet eye lens.

The objective has slight inward coma to correct the coma of the eyepiece.

So a 10 element eyepiece.
When designed about 1919 only simple glass types were available.

It wasn't until 1938 that Kodak designed lenses using thorium glass with the Aero Ektar in production in 1940.
Kodak also used thorium glass in their large wide field eyepieces.
This glass was used until 1975, but was replaced with non radioactive glass types from the 1950s onwards.
By the 1970s exotic glass was available, which had to be immediately coated to stop tarnish.

So by the mid 1970s the Dennis Taylor eyepiece could be made with 7 or 8 elements.

Now these type of eyepieces can be made with 6 or 7 elements.

The paper discusses a 10x prismatic binocular, but also mentions a 7x binocular.

H. Dennis Taylor was in a class of his own.

B.
 
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Omid

Well-known member
United States
Thank you so much Binastro for your research (posts 180-186)!!

My apologies for delayed response. This week I am participating in a series of meetings with the National Science Foundation who is now one of my major R&D sponsors. Our meeting was originally located at the NSF headquarters in Washington DC but I and more than a hundred other attendees had to cancel our travel reservations due to the corona virus. Now, we are meeting via conference call but still use East Coast time as our reference meaning I am getting up every day at 5 AM to attend the meetings! ;)

I am going to look up the paper you cited and read it. I did some further research myself. Smith's book (Modern Optical Engineering, 4th edition) does a nice step-by-step review of the design of a Keplerian telescope with lens-based erector in Chapter 13 (pp. 296-303). Smith's analysis is for thin lenses and uses same logic as my own simple analysis presented in my previous post.

Your finding that a negative field lens increases eye relief is consistent with the theory that the exit pupil is the image of the aperture stop as seen through the eyepiece. A field lens changes the position of the aperture stop image without affecting magnification. A positive field lens at objective focal plane reduces eye relief. A negative field lens, increases it.

-Omid

PS. Found the paper! :)
 

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Omid

Well-known member
United States
While birds fly freely in the sky and humans* are locked down in their nests, I have been thinking of how to design a better (longer and wider) eye-box for a certain telescopic instrument. As part of my research, I figured that my theory in post #179 is correct: The exit pupil is the image of the aperture stop as formed by the eyepiece so it's position depends on where the aperture stop is. However, as the focal length of most telescope eyepieces is rather short (10mm-20mm) and the objective lens focal length is relatively long (f around 1000m), the aperture position (=objective lens position) is rather far and its exact location will not shift the exit pupil position much. In this case, eye relief (=the exit pupil location) becomes a property of the eyepiece.


* In the "golden era" before the virus, urban human beings who had the privileges of "higher education" and "living in a metropolitan" such as New Yok or London or Hong Kong or Toronto or Tokyo would start their day waking up in a finely decorated shoebox (apartment) in a tall anthill (high-rise building). They would then descend through a metal box (elevator) into an underground burrow like those made by mole rats. There, they would enter another metal box (underground subway) that would take them to a different ant hill (office tower) in which they would "sit" in a cubical looking at an LCD screen and pressing bottoms on a keyboard. During their "free time" at lunch, these human beings would look at a smaller screen (mobile phone) and immerse themselves in the social media "buzz" created by millions of other similar creatures. Such glorious life for the only mammal on earth who evolved as a hunter capable of both stereoscopic vision and endurance running :(
 
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Troubador

Moderator
Staff member
Supporter
If a Barlow is inserted, then the magnification can change radically depending on the position of the Barlow.

B,

This is how Zeiss's FL 8x32 became a 10x32 and why it was never claimed that FL 10x32 had a field flattener: because the Barlow was there to lift the magnification not to flatten the field.

Lee
 

John A Roberts

Well-known member
Australia
Just to clarify:

A) The Zeiss FL 10x32 has 2 additional lenses compared to the 8x32:

FL 10x32 CONSTRUCTION

The FL 10x32 has 11 lenses per side (along with the 2 prisms)
The construction is specifically noted by Zeiss in this page about Lens Concepts - see the last paragraph:
https://www.zeiss.com/sports-optics.../competences/lens-concepts.html#lens-concepts

In contrast the FL 8x32 has 9 lenses per side, as can be seen in the attached cross-section

And as indicated by Henry, it's likely that the extra 2 lenses would be used as an eyepiece doublet

John

p.s. the 8x32 image clearly shows the space where the extra 2 lenses could be placed

Although the link to the Zeiss page is no longer active, see the screen grab, along with a copy of the 8x32 image referred to


B) And for context, see the discussion in the thread prior to my post, especially from post #9 on: https://www.birdforum.net/showthread.php?t=375091
i.e. as Lee indicates, any field flattening would have been an incidental consequence of adding the additional lenses to alter the magnification


John
 

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Steve C

Well-known member
A very experienced Spanish optics expert, Rafael Chamón Cobos, has developed an ingenious method for collimating binoculars.

It is described here:
https://sites.google.com/site/rafaelchamoncobos5/home/setup-with-mirror

I'm unqualified to assess the utility of the method, but Holger Merlitz posted an appreciative comment, so it surely deserves consideration.

Thanks for the link. That looks interesting. I just might build one of these to tinker with. I have some older duplicate binoculars that I can sacrifice to education if I mess up. Might be interesting to see Bill's take on this.
 

Omid

Well-known member
United States
Collimation is difficult!

Hello all,

I am glad to see that you guys are well! The white paper by Mr. Cobos on binoculars' collimation is very interesting. I remember reading a previous version of his article more than a year ago. I was very impressed by it. Mr. Cobos' original paper corroborated my findings about the ill-posedness of optical beam steering using a Risley prism pair. It also inspired a new invention in a totally different field (side-by-side double rifles).

Collimation of binoculars by adjusting objective lens positions housed in eccentric rotatable rings causes two fundamental problems:

A- Requires solving an ill-posed inverse problem: It is straightforward to calculate where the optical axis of each objective lens is given the rotational position of each eccentric ring (i.e. forward problem is well-posed). However, the inverse problem of calculating the rotational positions that would produce a desired lens axis position is ill-posed. This is because the problem does not have a unique solution and, worse, the solutions are unstable. A small change in the required position of the lens center might require a very drastic change in the rotational position of the rings. This is why Mr. Cobos has to rely on a spreadsheet to help solve the problem and even then, it will take multiple iterations to solve the problem.

B- Shifting objective lens axes will destroy internal collimation of each barrel: If each individual barrel is adjusted in the factory such that all the lenses are on the same axis, then any additional shift to the position of the objective lens to achieve collimation between the two barrels will destroy the internal collimation of individual barrels.

The above problems are not faults of Mr. Cobos's method. They are faults associated with the way binocular's are constructed. I wonder if all modern binoculars are collimated by shifting their objective lenses or by shifting their erector prisms? Is there any other way? How do Leica, Swarovski, etc. collimate their binoculars in the factory?

-Omid
 
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WJC

Well-known member
Hello all,

I am glad to see that you guys are well! The white paper by Mr. Cobos on binoculars' collimation is very interesting. I remember reading a previous version of his article more than a year ago. I was very impressed by it. Mr. Cobos' original paper corroborated my findings about the ill-posedness of optical beam steering using a Risley prism pair. It also inspired a new invention in a totally different field (side-by-side double rifles).

Collimation of binoculars by adjusting objective lens positions housed in eccentric rotatable rings causes two fundamental problems:

A- Requires solving an ill-posed inverse problem: It is straightforward to calculate where the optical axis of each objective lens is given the rotational position of each eccentric ring (i.e. forward problem is well-posed). However, the inverse problem of calculating the rotational positions that would produce a desired lens axis position is ill-posed. This is because the problem does not have a unique solution and, worse, the solutions are unstable. A small change in the required position of the lens center might require a very drastic change in the rotational position of the rings. This is why Mr. Cobos has to rely on a spreadsheet to help solve the problem and even then, it will take multiple iterations to solve the problem.

B- Shifting objective lens axes will destroy internal collimation of each barrel: If each individual barrel is adjusted in the factory such that all the lenses are on the same axis, then any additional shift to the position of the objective lens to achieve collimation between the two barrels will destroy the internal collimation of individual barrels.

The above problems are not faults of Mr. Cobos's method. They are faults associated with the way binocular's are constructed. I wonder if all modern binoculars are collimated by shifting their objective lenses or by shifting their erector prisms? Is there any other way? How do Leica, Swarovski, etc. collimate their binoculars in the factory?

-Omid

Where do I begin to tell the story .... Oops, wrong intro.

I see no way to address this issue without stepping on the toes of a couple of people who I respect immensely and who are, without a doubt, smarter than me.

Omid states: “Shifting objective lens axes will destroy internal collimation of each barrel:”

The word “will” should be replaced with “could.”

ANY movement of the objective WILL shift the line of sight. However, considering improvements in the art of lens making, improvements in CNC machining, and the observer’s spatial accommodation—obviously not considered in his calculations—more often than not, this will become a non-issue. Attached is a photo of Eric Magnusson—former Navy OM2—centering the elements of a 3-inch objective from a 1943 Quartermaster Glass. We had to recement the crown and flint elements because optical quality can suffer if the elements are not concentric.

In situations in which there is not enough motion in the eccentric to achieve collimation, there are other simple methods to correct this deficiency.

1) Objective lenses can be swapped telescope to telescope.
2) The objective lens can be turned in 90-degree increments—in its cell—on either OR both sides.
3) Finally, if the above doesn’t work, a tiny shim can be placed between the lip of the inner eccentric ring and the front of the lens. This is certainly not the best way, but in extreme cases, it IS a viable option. By tiny, I don’t mean 1/4 -inch. I’m referring to a displacement of .002-.004-inch. This is on the face of the crown element. However, I have seen places in which a larger shim on the SIDE of the ring would be practical.

By using eccentric rings in the alignment process, you are moving the line of sight LATERALLY, which means the objective has been removed from causing problems with third-order aberrations which is always an issue with the through-the-body/prism-tilt collimation convention. And while the increase in third-order aberration is a reality. It is usually so slight as to only be a concern for the irrational optical nitnoids who have to have something to worry about. Also, while the collimation of the optics in “Each Barrel” is part of the whole, it usually represents such a tiny part of the overall condition as to be inconsequential, easily fitting into the range of Spatial Accommodation of the most sensitive observer. It’s the line of sight of one telescope to the other and the optical axis that really matters. This may be troublesome for optical postdocs but very rarely is for experienced technicians. Enjoyable binocular images do not originate from the result of algebra or geometry but rather practical knowledge, the right test setup, skillful hands, and sometimes a touch of patience.

Finally, while there are those who find problems behind every bush, the following may be a calming agent:

An exhaustive survey for the Armstrong Aerospace Medical Research Laboratory in May of 1986 revealed in part:

“Indeed, a degree of alignment error unnoticed by, or even undetectable by, one observer may be unacceptable to another.” And ... “Zero optical tolerances and zero for image difference are not practical: they would be too difficult and expensive to obtain and could not be retained in use.”

While my credentials in academic optics are not even a good shadow of those possessed by Omid, having collimated thousands of binoculars, offered contributions to Zemax lens design software, and been an invited speaker on the subject to the optical engineers of SPIE, where I added to the vernacular, I think I have a pretty good handle on binocular collimation.

Rafael:

I have great respect for this man. He has been on the front lines of teaching the basics of the process for years. The problem I see with his work—for me—is all the reading, UNDERSTANDING, setups, calculations, and documentation involved.

His first program took up 31 pages, required the use of a moving sun, not hampered by cloud cover—possibly for days—rain, etc. when a much simpler and more efficient setup with an 8-inch telescope and a handheld, low-power auxiliary telescope was possible. BUT, did that stop him? Nope! He devised a method using auto-collimation and projection. A heavy, expensive, and complicated projection system was also devised by the US Navy in the MK13 binocular collimator. It fell into disuse and for several good reasons. (Mk 13, attached)

Most of my time with binocular collimation has been in a professional setting. Thus, I had to get swiftly to the brass tacks.

But Rafael has been driving like a dedicated 17th-century optician to bring new and useful concepts to all of us. Those who piggyback on his work will learn what they need to about binocular collimation and will undoubtedly make further contributions in streamlining. :cat:

Congrats and keep up the good work, Rafael!

Bill

PS There ya go, Steve.
 

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Omid

Well-known member
United States
Hi Bill!

Very glad to see that you are there and happily active in the shiny and virus-free realm of optics! (I was actually thinking of sending you a PM and asking you to please comment on the topic of collimation here in this thread. You beat me to it.)

Regarding shifting the objective lenses laterally, this will actually cause an "angular tilt" in the line of sight, not a "lateral shift". (An angular tilt is what's needed to make the line of sight f both barrels parallel.)

My concern, and you seem to agree with me, was that shifting the objective around in its housing will cause a misalignment with regards to the rest of the optical elements inside the binoculars. I am not sure how bad the ramifications are but we all know that having a decentered lens is not ideal in a telescope. It would have been nicer if binoculars used an alignment method that would not cause internal element-to-element misalignment.

Regarding the work by señor Cobos, I fully agree with you. What he is doing is very impressive and deserves greater recognition.

-Omid
 
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WJC

Well-known member
Hi Bill!

Very glad to see that you are there and happily active in the shiny and virus-free realm of optics! (I was actually thinking of sending you a PM and asking you to please comment on the topic of collimation here in this thread. You beat me to it.)

Regarding shifting the objective lenses laterally, this will actually cause an "angular tilt" in the line of sight, not a "lateral shift". (An angular tilt is what's needed to make the line of sight f both barrels parallel.)

My concern, and you seem to agree with me, was that shifting the objective around in its housing will cause a misalignment with regards to the rest of the optical elements inside the binoculars. I am not sure how bad the ramifications are but we all know that having a decentered lens is not ideal in a telescope. It would have been nicer if binoculars used an alignment method that would not cause internal element-to-element misalignment.

Regarding the work by señor Cobos, I fully agree with you. What he is doing is very impressive and deserves greater recognition.

-Omid


Hi Omid,

— At my age—and with underlying health issues—if I get it ... I’m gone.

Regarding shifting the objective lenses laterally, this will actually cause an "angular tilt" in the line of sight, not a "lateral shift". (An angular tilt is what's needed to make the line of sight f both barrels parallel.)

— If you take a raw cemented doublet objective in your left hand and transfer it to you right hand, you will find that incident rays striking any portion of the lens, at any angel, will leave that lens at the exact prescribed location and the image formed by the bundles incident across its face will produce the exact number and magnitude of 3rd-order aberrations.

I can see your point should you be speaking of two or three-element AIR SPACED objectives.

Since I haven’t known everything since I was 17 ... If I am wrong, please teach me. It is so much nicer being here than on Cloudy Nights, where they are collecting pathological liars who enjoy getting their egos stroked by those who lack the experience to know they are being led down non-productive paths.

My concern, and you seem to agree with me, was that shifting the objective around in its housing will cause a misalignment with regards to the rest of the optical elements inside the binoculars. I am not sure how bad the ramifications are but we all know that having a decentered lens is not ideal in a telescope. It would have been nicer if binoculars used an alignment method that would not cause internal element-to-element misalignment.

— Just as the novice often has a swelling in the chest after totally disassembling his binocular and photographing the components with seemingly no regard for subsequent realignment:

“ ‘Colyumnation’ ... what’s that?”

... I have found that most of those with your credentials overthink the essentials by a good measure. I maintain—and will until you teach me differently—that moving the objective laterally only alters the line of sight based on the principle ray striking subsequent optical elements—that deviation based on the aggregate of any number of tilted and decentered components. I think our differences lie in thoroughly understanding each other.

Regarding the work by señor Cobos, I fully agree with you. What he is doing is very impressive and deserves greater recognition.

— Rafael is to be appreciated and commended. I believe he has at least another iteration in him. He is going to be hard-pressed to come up with a simpler method of binocular collimation than is possible with an 8-inch or larger telescope and an auxiliary—available from Cory Suddarth. Most people who are interested in binocular collimation are not interested in lengthy circumlocutions; they just want to get the job done. Rafael has done so much and knows the math and what needs to be done, I look to him to find a way to streamline. However, even if he doesn’t lift a finger, he has already done some fantastic deeds for the cause. :cat:

Bill
 
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Omid

Well-known member
United States
A Review of Binocular Collimation Method

Hi Bill,

Thank you again for your comments. I am a student of binocular optics. I try to underestand optics problems by explaning them clearly to myself (and sometimes to others). Please see the attached presentation in which I have explored two topics:

a) How a lateral shift of the objective lens tilts the line of sight in telescopes and cameras.
b) Why adjusting binocular's collimation by eccentric rings gets so complicated.

I did not cover the sobject of how (if) laterally shifting the objective lens affects abberations such as coma, astigmatism, etc. as seen through the eyepiece. We'll leave that topic to another time (other members of the forum, you are welcome to comment on this topic).

I spent more than 6 hours making the presentation that I have attached. I hope you and other forum members enjoy it.

-Omid
 

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WJC

Well-known member
Hi Bill,

Thank you again for your comments. I am a student of binocular optics. I try to underestand optics problems by explaning them clearly to myself (and sometimes to others). Please see the attached presentation in which I have explored two topics:

a) How a lateral shift of the objective lens tilts the line of sight in telescopes and cameras.
b) Why adjusting binocular's collimation by eccentric rings gets so complicated.

I did not cover the sobject of how (if) laterally shifting the objective lens affects abberations such as coma, astigmatism, etc. as seen through the eyepiece. We'll leave that topic to another time (other members of the forum, you are welcome to comment on this topic).

I spent more than 6 hours making the presentation that I have attached. I hope you and other forum members enjoy it.

-Omid

Hi, Omid,

Glad to hear from you, too; we have been miscommunicating.

Lateral movement of a 2-element, cemented objective, in and of itself, cannot alter 3rd-order aberrations. Only when striking the next, or subsequent elements, (lenses, prisms, or windows) is that even a possibility. You are speaking academically; I am speaking practically of real-world binocular repair and collimation. The slight lateral movement of the objective is practically irrelevant, compared to the decentering or tilt of one or more elements in a prism cluster or EP—where differences in thickness, wedge, or glass type must be considered.

You also wonder, “... why adjusting binocular's collimation by eccentric rings gets so complicated.”

To the head-scratching postdoc and the novice looking for brownie-points from the group for all his in-depth geometric drawings and equations, it’s “so complicated.” However, for the guy who has used the skill every workday for years, it is not any more complicated than riding a bicycle—possibly less ... I’ve never fallen off an eccentric ring.

I was required to learn all those equations and drawings while in “A” school. But Master Chief Lou Corriveau told me that should he see me, “using all that math BS"* once we were in the fleet, he would no longer consider me an Opticalman. Cory uses that stuff when offering one of his classes. And he should. But if I saw him wasting that kind of time when he was working for me, he wouldn’t have been working for me that long. Fortunately, he’s been my best friend for 44 years and can collimate binos in his sleep ... just like his chief. :eek!::cat:

* I watered that down a lot!

Bill
 
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Omid

Well-known member
United States
Hi, Omid,
… Lateral movement of a 2-element, cemented objective, in and of itself, cannot alter 3rd-order aberrations. Only when striking the next, or subsequent elements, (lenses, prisms, or windows) is that even a possibility.

Bill

Hi Bill,

Exactly as you said: The aberrations produced by the objective lens group don't change if it shifts laterally. What is affected is the possibility of cancelling out some of these aberrations by subsequent lenses. As we all know, binoculars are designed such that some of the aberrations produced by the objective (e.g. secondary spectrum, spherical aberration and field curvature) are cancelled out in the eyepiece. If the objective and eyepiece are not centered, than the cancellation will not go as planned and the magnitude of final aberrations increases.

Also as you said, these concerns might be purely academic. A similar situation occurs in riflescopes when the erector lenses are deliberately miss-aligned to adjust for point of aim. It seems that in both binoculars and riflescopes the misalignment does not cause a noticeable degradation in image quality.

-Omid
 
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WJC

Well-known member
Hi Bill,

Exactly as you said: The aberrations produced by the objective lens group don't change if it shifts laterally. What is affected is the possibility of cancelling out some of these aberrations by subsequent lenses. As we all know, binoculars are designed such that some of the aberrations produced by the objective (e.g. secondary spectrum, spherical aberration and field curvature) are cancelled out in the eyepiece. If the objective and eyepiece are not centered, than the cancellation will not go as planned and the magnitude of final aberrations increases.

Also as you said, these concerns might be purely academic. A similar situation occurs in riflescopes when the erector lenses are deliberately miss-aligned to adjust for point of aim. It seems that in both binoculars and riflescopes the misalignment does not cause a noticeable degradation in image quality.

-Omid

Hi, Omid,

'Looks like we're back on the same page, now! :t::cat:
 

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