Focussing: Just Do It! (1 Viewer)

[Maljunulo]

I don't understand why when I focus on something several hundred yards away, I still need to change the focus to look at things even further away. Is it because my old nearsighted eyes lack accommodation?

How do binoculars work for people who have artificial lenses giving them no accomodation?

1. No, you have to refocus because the binocular cannot accommodate at all. Its lenses cannot change shape.

2. They work the same as for anyone else. The focus wheel “accommodates” the binocular to your vision. (in the absence of astigmatism, etc)

 

[Binastro]

The difference in focus with a binocular between the Moon and any star is I think one two millionth of a mm.
That is one wavelength of light.

As to the change in focus on the Moon and stars, it could be night vision versus day vision, but in my case spherical aberration may be involved when I see a bright full Moon in stereo with the 20x60.

Regards,
B.

 

[Binocollector]

I think I need to dust off my good old 20x60 Tento ...

 

[Scott98]

I never did that with binoculars or telescopes.

I focus on a star, then move to the moon. It works every time, and fiddling the focus never did improve it.

Add me to the “If it’s at infinity, it’s at infinity.“ crowd.

yes, of course....the Moon and stars are both at infinity....Luna is 250,000 miles away! Not a few hundred yards. The edge of the moon's disk is a great place to set your focus for an astronomy session

 

[Maljunulo]

It would be an interesting experiment to put astrographic plates of the same field, taken six months apart, under a stereo comparator.

I suspect that except only a very few stars are so close enough to “pop out” and appear to be in front of the rest of the field. I’m not sure our eyes would see it.

 

[Eric_D]

I came to this thread trying to discover whether a topic, about which I was going to launch a new thread, had already been covered or answered. I am still not sure, as the thread is rather non-linear, to say the least. Awesome expertise displayed, but I may post on a DOF thread instead ...

The topic of triggering accommodation is interesting:

...
Longitudinal chromatic aberration does seem to check the box for providing the direction for accommodation, too.

However, if that's the primary mechanism, there are secondary mechanisms as well? For example, it's possible to focus under monochromatic lighting where chromatic aberration is absent.
...
Henning

Vergence-accommodation conflict​

(Wikipedia)
is another obvious candidate, and should have been well-studied, since the advent of headache-inducing VR/AR/XR virtual reality headsets ...
As well as Apple, who are in the news, 'Magic Leap' blew $4 billion with a lot of perceptual effort on a very short-lived product.

[...] Our eyes have CA, so the colour of the Moon and stars, although seemingly the same are often slightly different.[...]

Incidentally, on one of the specially made 20x60 USSR binoculars made for a dozen astronomers that were hand made to high tolerances I always saw the Moon in full 3D even though it obviously isn't.
I don't know the reason.

Red stars have a different focus to white stars. [...]

Sounds like 'Longitudinal Chromatic Aberration' LCA or LoCA well-known to MILC photographers using analog film-era lenses on digital cameras.
I wonder if the '3D moon' relates to the 'rolling ball' or 'globe' effect researched by Holger Merlitz? The one used to excuse pincushion distortion ... I don't perceive that ... yet.
I prefer to use stars for 'diopter' adjustment, in case the moon brightness expands the iris (or contracts the pupil). Perhaps spherical aberration could lead to the need to refocus for the edge vs the centre of the aperture? Could test with ring and disc apertures? (Yes, I could be talking about aberration of the bins or the eye here ... like 'compensating eyepieces' that had +SphAbb in microscopes to balance -SphAbb in objectives ...)

On the original topic (I think) of this thread, I would like to add notes that the British Army (or perhaps Royal Marines more specifically) bravely adopted a fixed-focus (-(or+?)1 dioptre) binocular, the Avimo L12A1 7X42. Later badged Rollei and Belomo, who might still make or repair them.

A very interesting paper on prototype Avimo 7x42 prototype designed for the UK armed forces in the 1970s and in service in 1979 as the Type L12A1.

Funky bins
ROLLEI 7 x 42 GA

I thought "roof prism" was a typo but it isn't. The original design was a roof and they switch to sort of 45° "over-under" porro for the actual issued design. There is also a similar monocular roof prism prototype.

http://www.binoculars-cinecollectors.com/Avimo_prototype_7x42_and_military_model.pdf

Finally they're apparently "focus free" bins and set of -1D focus (not at infinity). I presume setting for hyperfocal distance. I guess designed for corrected vision with good accommodation (young solidiers). I previously assumed they were IF previously but apparently not! Obviously not good birding bins.

Holger also reviews these bins
Review: Military 7x40 binoculars

Avimo 7x42 Military Binocular​

Not a birding bin !! but might be interesting.

A nice example of a fixed focus 7x42 binocular made by Avimo for the UK military, ...

Also discussed by Frank on Flickr

“A further advantage is that the vergency tolerance is not as critical when compared with conventional instruments having parallel axes”

That suggests a degree of 'toe-in' so that the field-of-view outer circles coincide with objects nearer than infinity?
Like Pentax Papilio? Military use will mostly be at a distance: perhaps this is a way of stretching the field-of-view with overlapping circles?

I vaguely remember much research being done and documented before going fixed-focus - possibly archived by Anne & Terry Vacani who have some unique prototypes!
I am sure there are threads here disparaging autofocus, focus-free binoculars, but this is a well-researched serious counter-example. In military applications, the ruggedness and instant readiness has considerable value.
There was even a British pre-WW1 example without an IPD hinge! (Aitchison reverse porro) Could use long-eye-relief eyepieces and use part of the field of view?

The Avimos certainly have some off-axis chromatic aberration, but are really nice and unfussy.

I only acquired half a pair - the popular 'monocular conversion' could be effected in the field by whacking them on the knee or a swift kick, apparently, probably trade the other half for a bar of chocolate? They suit me, as I have one eye naturally focussed at infinity, the other at reading/screen distance - 'perfect' vision without glasses, despite reduced acommodation aged 60+ ...
I also have some other bins with a diopter adjustment that doesn't quite go far enough ... but that is one for the DOF thread ...

People say they were unpopular in action, because the over-under design left your head exposed above the parapet of a trench, but I am sure the resourceful soldier would have inverted them as periscopes ... much dubious binocular 'lore' about ...

Oh, I think the Avimo was issued to all soldiers: after 30 years with the Avimo, the Army went with Steiner, and Royal Marines with a 'Pyser-SGI' made in Nikon's factories.

 

[Patudo]

It'd be interesting to know the results of any comparitive tests/evaluations between the Avimo and other NATO (or indeed Warsaw Pact) binoculars eg. Hensoldt service glasses in 8x30 or 10x50, or the well known East German 7x40s.

 

[John A Roberts]

Further to Eric's post #126 . . .

The original text about the collimation and vergence of the Avimo, is in an article by William Reid
'Binoculars in the Army, Part IV', National Army Museum, London, 1984.
See paragraphs 3 and 4:




It’s on the third page of Frank’s (aka LPT here on BirdForum) flickr series on the Avimo, starting with:

https://flic.kr/p/ftzrBz

- - - -
And an illustrated 23 page PDF by the Vacanis' - primarily concerning the roof-prism prototype of the Avimo - can be found at: Binoculars
(go down the page to 'Articles by Anna & Terry Vacani').


John

 

[Tringa45]

The original text about the collimation and vergence of the Avimo, is in an article by William Reid
'Binoculars in the Army, Part IV', National Army Museum, London, 1984.
See paragraphs 3 and 4:

Well, I think Mr. Reid must have misunderstood something and I hope Bill Cook doesn't read this as it would give him palpitations!
Assuming objective spacing and IPD are approximately equal, a convergance of the optical axes to the hinge axis at 1 m would be 1,86° for each barrel at 65 mm objective spacing, or 112 arcminutes.
According to Bill, the US Navy collimation tolerance was 2 arcminutes divergance or 4 arcminutes convergance.

John

 

[WJC]

Well, I think Mr. Reid must have misunderstood something and I hope Bill Cook doesn't read this as it would give him palpitations!
Assuming objective spacing and IPD are approximately equal, a convergance of the optical axes to the hinge axis at 1 m would be 1,86° for each barrel at 65 mm objective spacing, or 112 arcminutes.
According to Bill, the US Navy collimation tolerance was 2 arcminutes divergance or 4 arcminutes convergance.

John

Bill Cook didn’t quote those tolerances. He was just repeating the words of the US Navy Opticalman tech manual, NAVEDTRA 10205-C. I also pointed out those specs can be found in other books (see attached). While Opticalman 3&2 was listed 6th on the list, three things should be noted:

1. It was the US Navy that originated the alignment procedure for binoculars and developed the first successful collimators.

2. As professor G. Dallas Hanna has noted that collimation technique were considered hush, hush during the war and technicians (Precision Artificers before they became designated Opticalmen in 1948) did their work based on a few mimeographed pages and word of mouth.

3. As Chief Opticalman ... me ... has pointed out, ANY of those tolerances will work just fine, but when spatial accommodation (something not mentioned in those days) is considered, the original Navy standards may be a bit over the top. Overall, I choose to use Dr. Johnson’s standard (also attached.)

As far as those who want to speak of Steiner and other non-electronic “auto-focus” binoculars, I must defer to Plato:

“A wise man speaks when he has something to say; a fool when he has to say something.”

 

[Tringa45]

Bill Cook didn’t quote those tolerances.

Your book, Bill, page 94, or was there some misunderstanding?
I was merely pointing out that if the Avimo had really been "collimated" to a convergence of 112 arcminutes as inferred in §3 by William Reid in John Robert's post #128, then viewing at infinity would be almost as problematical as with a correctly collimated binocular at 1 m. Merging the images would be extremely stressful.

John

 

[John A Roberts]

In Frank's flickr series about the Avimo, the 4th screen is about the commercial version offered by Rollei.

The promotional sheet from Rollei:
a) states that the fixed focus enables instant viewing at all normal ranges (see the second 'Unique Feature' heading), and;

b) again seems to indicate that the focus is set to 1 meter (the first dot point):




However, when my Swarovski Habicht 7x42 is set to its nominal minimum focus distance of 3.5 m (11.5 ft),
it fails to gave a usable image beyond 10 m or so.
And when my Zeiss FL 7x42 is set to its nominal minimum focus distance of 2 m (6.5 ft), it fails to give usable image at 3.5 m!
So . . . 🤷‍♂️


In addition, Steiner states in relation to its 'Sports Auto Focus' feature, that setting the individual eyepiece focus to 100 m
results in everything from 20m on out being in focus. See at: FAQ


And in Holger's review of various military 7x42's, including what seems to have been an original condition Avimo,
the Avimo's fixed focus wasn't a notable limitation in relation to the on-axis sharpness, see at: Review: Military 7x40 binoculars


So unless the Avimo had some 'super secret optical sauce', the knowledge of which has been lost over the years,
the actual set focus distance must be more like the Steiner recommendation.


John

 

[WJC]

Your book, Bill, page 94, or was there some misunderstanding?
I was merely pointing out that if the Avimo had really been "collimated" to a convergence of 112 arcminutes as inferred in §3 by William Reid in John Robert's post #128, then viewing at infinity would be almost as problematical as with a correctly collimated binocular at 1 m. Merging the images would be extremely stressful.

John

Roger that.

Bill

 

[WJC]

In Frank's flickr series about the Avimo, the 4th screen is about the commercial version offered by Rollei.

The promotional sheet from Rollei:
a) states that the fixed focus enables instant viewing at all normal ranges (see the second 'Unique Feature' heading), and;

b) again seems to indicate that the focus is set to 1 meter (the first dot point):

View attachment 1560595


However, when my Swarovski Habicht 7x42 is set to its nominal minimum focus distance of 3.5 m (11.5 ft),
it fails to gave a usable image beyond 10 m or so.
And when my Zeiss FL 7x42 is set to its nominal minimum focus distance of 2 m (6.5 ft), it fails to give usable image at 3.5 m!
So . . . 🤷‍♂️


In addition, Steiner states in relation to its 'Sports Auto Focus' feature, that setting the individual eyepiece focus to 100 m
results in everything from 20m on out being in focus. See at: FAQ


And in Holger's review of various military 7x42's, including what seems to have been an original condition Avimo,
the Avimo's fixed focus wasn't a notable limitation in relation to the on-axis sharpness, see at: Review: Military 7x40 binoculars


So unless the Avimo had some 'super secret optical sauce', the knowledge of which has been lost over the years,
the actual set focus distance must be more like the Steiner recommendation.


John

Maybe, if I'm really good, God will give me 5 minutes alone with the idiot who started all this AUTO-FOCUS/FIXED-FOCUS garbage that only works for those dumb enough to believe it! It seems too many people can't figure out the realities of the matter!

 

[Patudo]

It'd be pretty impressive if the Avimo had a close focus of 1m - isn't close focus for the NL "only" 2 metres?

 

[Eric_D]

I would interpret it as that the eye is focussed at one metre, while the binoculars focus at ~infinity.
Also perhaps the eyes converge to one metre, too. (As in avoiding 'Vergence-accommodation conflict')
I guess that reduces the binocular axes' vergence by a factor of 7. Possibly the binoculars focus on 7m object-side to give 1m eye-side? (No, that is naive thinking ... probably 500m as in Steiner above)
But hey, advertising-speak is rarely precise or accurate.
Steiner seem to be relying on 'hyperfocal distance': eye accommodation makes it a little different from photography, though.

objective spacing and IPD are approximately equal

That is yet another interesting design choice: it harks back to pre-WW1 Ross-Barton and Huet ² ³ military designs, avoiding Zeiss' patent for using wider objectives for enhanced stereoscopic depth. That patent lapsed in 1908. Here the only benefit I can see is compactness. Perhaps they could be used as a stereo microscope, in reverse? Unusual on the battlefield: microsurgery? Oh, military field microscopes are definitely a thing.

It'd be interesting to know the results of any comparitive tests/evaluations between the Avimo and other NATO (or indeed Warsaw Pact) binoculars eg. Hensoldt service glasses in 8x30 or 10x50, or the well known East German 7x40s.

Holger Merlitz is quite thorough in reviewing them.
DDR NVA DF 7x40, Romanian IOR-SA 7x40, Polish PZO 7x45, Chinese GG95 7x40, British Avimo 7x42, Austrian civilian Swarovski Habicht 7x42
'Interesting', but not in a good way ...
"The Avimo is especially interesting. It has got a quality coating, excellent low light performance, and high resistance against ghosting. Unfortunately, this impression is spoiled by a glossy finish of the inner tube walls, causing a stray light which could easily be avoided. Confronted with examples like that, I sometimes ask myself whether such an obvious defect could be left unnoticed during those field tests which are mandatory for defense projects. Apart from that, I dislike the fixed-focus feature of this binocular."

Thank you Bill for the extracts presumably from the book '(BINOCULARS: Fallacy & Fact: The Instruments, The Industry and You' available in all the best online stores) and Prof Johnson's table of tolerances from Imperial College. I understand 'convergence' and 'divergence'; I deduce that 'step' is vertical misalignment.

I interpret Reid's comment "vergency tolerance is not as critical" (as with parallel axes) to mean there is less risk of forcing the eyes to diverge, which would be completely unnatural for most of us.

I am perhaps lucky in being very tolerant of mis-collimation, having spent much time with stereo photography, both with viewers, and free-viewing either cross-eyed or parallel (even divergent?).
In fact I have discovered that my relaxed eyes naturally move their axes in quite different planes, the right eye about 10 degrees tilted. If I look out through a window with almost-closed curtains, such that one eye sees a street-light through the gap between the curtains, but the other eye 'sees' the light through the curtain fabric, converging and diverging the eyes also tilts one eye up and down, too! The fabric disrupts the image so that eyes/brain cannot 'fuse' two images into one.
In Unicode text, (may not work on all browsers and platforms)
←↗
Pehaps I have some chameleon genes?
I have very little success with Autostereograms though ...

With binoculars, I usually only notice mis-collimation when I return to the real world, blinking, crossing and uncrossing my eyes to reset them.
As well as individual people having different tolerance, the type of use of binoculars is also significant. I would probably be driven mad if star-gazing with mis-collimated bins: I could probably align any star with any other star, so getting them all aligned at once could take a while.

The Aitchison fixed-IPD reverse-porro binoculars I mentioned are here:

Pardon our interruption...

www.ebay.co.uk

A one-off failure? Or grandfather of modern compacts?
I suppose they could have been made in different IPD sizes: 'Small, medium, or large?' but I doubt it.
Aitchison did re-brand some French and German (Schütz Kassel/Cassel, Foth, Ruf) binoculars, so these may not be British.

I said

"Could use long-eye-relief eyepieces and use part of the field of view?"

instead of IPD adjustment. Of course, I meant 'large exit pupil', not long-eye-relief eyepieces. Sorry!
These do not have large exit pupils, at least not by modern standards.

 

[WJC]

I would interpret it as that the eye is focussed at one metre, while the binoculars focus at ~infinity.
Also perhaps the eyes converge to one metre, too. (As in avoiding 'Vergence-accommodation conflict')
I guess that reduces the binocular axes' vergence by a factor of 7. Possibly the binoculars focus on 7m object-side to give 1m eye-side? (No, that is naive thinking ... probably 500m as in Steiner above)
But hey, advertising-speak is rarely precise or accurate.
Steiner seem to be relying on 'hyperfocal distance': eye accommodation makes it a little different from photography, though.


That is yet another interesting design choice: it harks back to pre-WW1 Ross-Barton and Huet ² ³ military designs, avoiding Zeiss' patent for using wider objectives for enhanced stereoscopic depth. That patent lapsed in 1908. Here the only benefit I can see is compactness. Perhaps they could be used as a stereo microscope, in reverse? Unusual on the battlefield: microsurgery? Oh, military field microscopes are definitely a thing.




Thank you Bill for the extracts presumably from the book '(BINOCULARS: Fallacy & Fact: The Instruments, The Industry and You' available in all the best online stores) and Prof Johnson's table of tolerances from Imperial College. I understand 'convergence' and 'divergence'; I deduce that 'step' is vertical misalignment.

I interpret Reid's comment "vergency tolerance is not as critical" (as with parallel axes) to mean there is less risk of forcing the eyes to diverge, which would be completely unnatural for most of us.

I am perhaps lucky in being very tolerant of mis-collimation, having spent much time with stereo photography, both with viewers, and free-viewing either cross-eyed or parallel (even divergent?).
In fact I have discovered that my relaxed eyes naturally move their axes in quite different planes, the right eye about 10 degrees tilted. If I look out through a window with almost-closed curtains, such that one eye sees a street-light through the gap between the curtains, but the other eye 'sees' the light through the curtain fabric, converging and diverging the eyes also tilts one eye up and down, too! The fabric disrupts the image so that eyes/brain cannot 'fuse' two images into one.
In Unicode text, (may not work on all browsers and platforms)
←↗
Pehaps I have some chameleon genes?
I have very little success with Autostereograms though ...

With binoculars, I usually only notice mis-collimation when I return to the real world, blinking, crossing and uncrossing my eyes to reset them.
As well as individual people having different tolerance, the type of use of binoculars is also significant. I would probably be driven mad if star-gazing with mis-collimated bins: I could probably align any star with any other star, so getting them all aligned at once could take a while.

The Aitchison fixed-IPD reverse-porro binoculars I mentioned are here:

Pardon our interruption...

www.ebay.co.uk

A one-off failure? Or grandfather of modern compacts?
I suppose they could have been made in different IPD sizes: 'Small, medium, or large?' but I doubt it.
Aitchison did re-brand some French and German (Schütz Kassel/Cassel, Foth, Ruf) binoculars, so these may not be British.

I said

instead of IPD adjustment. Of course, I meant 'large exit pupil', not long-eye-relief eyepieces. Sorry!
These do not have large exit pupils, at least not by modern standards.

Yes, STEP is vertical displacement or DIPvergence.

Cheer, Bill