BINOCULAR COLLIMATION VS. Conditional Alignment

BINOCULAR COLLIMATION
VS.
Conditional Alignment
(And Why Knowing the Difference is Important)
B
inocular collimation is always a hot topic among amateur astronomers, bird watchers, and other naturalists. Internet sites dealing with binoculars are replete with stories of how some observer tweaked a few
screws and got his damaged binocular into “perfect collimation,” or made it “spot on,” or some bit of
verbiage meaning the same thing.
The problem with these claims is that while they are ego boosters and great conversation starters, they’re almost
always . . . WRONG!
Not in the sense that the instrument won’t provide a single user with adequate or even outstanding imagery. But
rather that the level of alignment more rightfully called “collimation” has been adversely affected in the process.
MYTHS, MIRTH, AND MISCONCEPTIONS
Spending 40 years in the optical business, ranging in positions from sales and repair to engineering and fabrication, I reel at the misinformation that abounds concerning the binocular industry and the consumer’s eagerness to
accept anything he hears from that industry or from local aficionados. And many are the facets of bino-lore that
have been reinforced by the “old wive’s tales” that have been going around for decades, and which have now been
sent into hyper-drive by the Internet.
Making matters worse is the fact that so many observers don’t understand the anomalies they’re trying to convey.
Many times I’ve heard, “My binoculars won’t focus,” when, in fact, the instrument focused just fine. But, with
the image smeared through poor collimation—and the consumer having never heard the word—or even knowing
binoculars need to be aligned— more often than not “focus” is thought to be the culprit.
LEVEL I TEST EQUIPMENT
Numerous articles depict devices to tell you if your binocular is collimated. Sadly, almost all concern themselves
with a lesser degree of collimation called conditional alignment only and not the 3-axis collimation all quality
binoculars have when they leave the factory. These authors are not trying to mislead anyone; they simply don’t
know the difference. And, after an exhaustive search of the Internet, and seeking help from the binocular buffs
who frequent the Cloudy Nights binocular forum sponsored by Astronomics, I have come to know why. The latest
treatise on 3-axis binocular collimation—available to the general public—was published by G. Dallas Hanna in
Amateur Telescope Making III, in 1953, and originated through his association with the California Academy of
Science while establishing a facility for the Navy to repair optical instruments used in the Second World War.
One easy-to-make setup to advise and to align binoculars is described by Jan Seyfried in his Choosing, Using,
and Repairing Binoculars, in Repairing & Adjusting Binoculars from Alii Service Notes, and in Collimators and
Collimation by Edmund Scientific. The main problem with these setups is in rigidity, as the collimator or binocular is slid side to side to address each of the binocular’s telescopes, or in having two collimating telescopes in the
procedure. With this arrangement one is left to wonder, “Are the collimators collimated?”
If you have to test a binocular to see if it is collimated, you really don’t need to! Why? We all have varying degrees of accommodation for misaligned instruments. If the deviation from parallelism is within the user’s range
of accommodation, the brain will merge the images. But, rely on accommodation too long and a headache may
result!
POPULAR USAGE
Did steam locomotives have tires or wheels?
With tires being rubber and wheels being
iron, it is obvious the answer is wheels,
right?
. . . . Wrong! Steam locomotives had steel
“tires” super-heated to expand before being
press-fitted onto the iron wheels where they
were allowed to cool, shrink, and grip with
tremendous adhesion. As in that example, binocular collimation today is merely that exercise which has come to
be known as collimation in popular usage. We seem to believe that if an instrument is aligned for one user . . . it’s
“collimated”! And it is as good as collimated . . . for that user or near that IPD (interpupillary distance)!
WHAT IS COLLIMATION?
Collimation means all the optics are aligned—or in a column—so that a light ray striking a given set of optics will
leave those optics at approximately the same angle it entered with the difference being related to a prescription
set by the lens designer.
A binocular is collimated in practical terms when the image from one telescope precisely overlaps the other with
no accommodation or eyestrain required. For 3-axis collimation to exist, this same superimposition of images will
exist at all IPDs. This means if a 6’ 6” man hands his binocular to his 6-year old daughter, they will both get the
same quality view.
WHAT IS CONDITIONAL ALIGNMENT?
A binocular may be “perfectly” aligned for a given IPD and still be out of collimation when the telescopes are
spread a bit or brought a bit closer together. Also, the extent of the problem is unpredictable, with the errors ranging from very slight to severe, depending on the displacement of element(s) in direction and distance. This is
called conditional alignment, with that condition existing only at an exact IPD for technical accuracy, or within
a varying small range of IPD settings well within the observer’s ability to accommodate errors in parallelism.
Some importers depend heavily on accommodation in both sales and repair to show their repair work or product
is good enough. But while I agree for most cases, this article is not about being “good enough” at or near a given
observer’s IPD; it’s about being aligned for all who pick up the instrument.
WHY IS UNDERSTANDING THE DIFFERENCE IMPORTANT?
Suppose on dropping your binocular you find the left telescope has been misaligned a little. Knowing the error
is in the left side, you can turn the correct alignment screws—or eccentric rings—and easily bring the binocular
back into 3-axis collimation.
But what if you buy into the notion of “all you have to do is . . . ,” and start tweaking screws on the wrong side?
You may perform a fine conditional alignment, but place the instrument farther out of 3-axis collimation by doing
so!
Thus we see that what binocular collimation is in a technical sense is quite different from what it is in everyday
usage.
NOTE: The dashed line in Figure 2 is to illustrate that misalignment of either telescope can be in any direction!
Figure 1
Figure 2
In Figure 1 above the red lines show a binocular collimated for a target at infinity. The green lines show that in
binoculars used for terrestrial observations, collimation should be set (in a perfect world) for targets a touch closer
than infinity. The images overlap without eyestrain and the view is pleasing.
Figure 2 illustrates what happens to the line of sight should the LEFT (or right) telescope be knocked out of alignment. The images are formed in slightly different locations. If they are close, the brain will try to compensate and
bring them together. If too far apart, a headache will result. KNOWING which side is not aligned to the axle is
essential to restoring 3-Axis COLLIMATION!
Figure 3 (at left) shows what can happen when the “Just turn these
screws” crowd gets involved. Conditional Alignment has been
achieved for one IPD, and the single user is happy. Yet, he or she DID
NOT “COLLIMATE” THEIR BINOCULAR—PERIOD! What could
have collimated the instrument, had the correct barrel (telescope) been
chosen for “tweaking,” is now rendering a good image at or near one
IPD, but damaging it at others.
Figure 3
Even as bad as misalignment appears to be, the drawing does not tell
the whole story. One might assume the optical axis of the right telescope has simply been shifted to match the left telescope. That, however, is rarely the case. The shift in most cases involves 3 dimensions.
Yes, the line of sight shifted left. But, did it also move up or down
some in the process!? Thus, the plot thickens, and perhaps our “Just
turn these screws” gang has been overstating the simplicity of a “collimation” job by a hefty margin!
Since most binoculars are not used at either the highest or lowest
IPD setting, the maximum errors in parallelism can often be ignored.
However, with collimation errors subject to the alignment AND tilt of
FOUR prisms and 2 objective lenses (in a simply Porro prism binocular), the exact cause of the displaced image is not easily ascertained.
And, this misunderstanding is not limited to amateurs. Many “professionals” at major importing companies just know how to “get it in the
box.” Cory Suddarth was with me the day I took a call from a fellow
who had been a repair manager at his company for more than 10 years.
His call went something like this: “Bill, I don’t understand it; I’ll get
the binoculars collimated, but when I move one of the barrels—it’s
off again!” His quandary is not unique, even among professionals.
This fellow had been selling Conditional Alignment as collimation all
those years. There’s a big difference between 20 years of experience
and one year of experience 20 times.
Also, people have a natural tendency to believe that every manufacturer (read: importer) has a team of experienced repair technicians at
the ready at all times. Sadly, this is not the case. Is accurately collimating binoculars difficult? Absolutely not! It’s just that some folks won’t
take the time to learn and some importers find that with consumers not
knowing about collimation, it’s a waste of profit to go the extra mile.
Accommodation Box A
Accommodation Box B
Collimation here isn’t “perfect” but nobody knows,
cares, or has reason to.
Conditionally Aligned
Accommodation Box A represents the Area of
Accommodation for a binocular of a given magnification as generally accepted by tests using observers of different ages and visual acuity.
The black cross in the center of the box represents
a “perfect” alignment of the collimated (to the
hinge) barrel. In this example only one telescope
is considered out of alignment
The red crosses represent the deviation from
“perfect” collimation at the full range of IPD settings.
If alignment allows both optical axes to fall within
this parameter (as in this example), the instrument
is collimated reasonably well, and the observer
can mentally ACCOMMODATE for the small error in alignment without squinting, eye strain, or
headache.
Accommodation Box B Illustrates that, while at some
range of IPD settings, the binocular will APPEAR to be
collimated, and MAY perform well at or near that setting, 3-Axis Collimation has been harmed in the process.
Thus, a slight error that could have been addressed with
the correct knowledge of collimation, has been turned
into a major problem when such knowledge is overlooked—allowing images at either extreme to resemble
the images in the illustration above.
The difference between Collimation and Conditional
Alignment will continue to be ignored by many long into
the future. It is nevertheless a mathematical fact of life
that all those who are serious about binocular observing
should recognize!
ACCOMMODATION
We all possess the ability to mentally merge slightly misaligned images without eyestrain or headaches. More often than not, this is what is being depended upon by the inexperienced observer with the jeweler’s screwdriver.
In SOME situations, this is just fine. But, if they haven’t learned to relax their eyes and STARE—letting the binocular do its work—the brain will grow weary of doing what the binocular should be doing and the observer will
start experiencing fatigue or headaches.
“I don’t know . . . it seems like the binocular is ‘DRAWING’ my eyes!”—frequently heard from consumers
‘CAN’T FORGET THE AXLE
In 3-axis collimation, the binocular’s hinge must be taken into consideration. In Hanna’s view, the hinge is the
“heart” of a binocular. Still, this vital piece of the process is almost never alluded to in popular literature today or
on the web. Even so, it is essential for true binocular collimation in which the instrument is aligned at all IPDs.
BUT JUST WHAT TOLERANCES ARE ACCEPTABLE?
How much can binoculars be misaligned before the observer finds it objectionable? In 1977 M.A. Ostrovskaya,
N.M. Putyatina, and I.N. Krivenko tested 16 subjects of various ages. Their conclusion, published in the October
1978 Soviet Journal of Optical Technology, was as follows:
“The maximum allowable deviation from parallelism of the ray bundles from the eyepieces in binoculars amounts
to 30 arcminutes vertically, and 40 and 100 arcminutes horizontally in the case of axis divergence and convergence, respectively, for most test subjects.”
In the U.S. Navy’s method of collimation, the goal was 2 minutes of divergence [lateral image displacement], 2
minutes of step [dipvergence, or vertical image displacement], and 4 minutes of convergence [image crossover].
Often considered too stringent—2 minutes is the best resolution the brain can discern—it should be remembered
that the procedure was developed at a time when marginal alignment could take an instrument out of service
faster. Also, a well-collimated binocular could be used the instant it was put to the eyes without waiting for an
adjustment for any errors in parallelism.
Are the specs really too stringent? Perhaps. Yet, none of my repair customers ever seemed to mind the extra attention to detail. Also, as writing instructors are prone to say: “It’s best to learn the rules of sentence structure and
grammar before setting about to break them.”
TAIL-OF-THE-ARC COLLIMATION
[The following instructions are for hand-held binoculars, only. Additional considerations must be made for large
tripod-mounted instruments that lack a central hinge.]
I cheer anyone with a collimation method that takes the binocular’s axle into account, and I can only hope this
article will inspire technical types to revitalize the craft. In today’s world in which affordable binoculars are being
made ever more shoddy, and user-collimation is considered a “feature”—instead of a production short-cut for a
manufacturer—such knowledge should not be forgotten.
When not using the pricey Fujinon U.B.M.M. (collimator), I used the truncated tail-of-the-arc method I learned—
and simplified—in the Navy’s Opticalman “A” school and a Navy Mk 5 collimator. I have read about and considered other methods, but for a variety of reasons, it is the one I feel best lends itself to amateurs. This is not to say
other methods don’t offer advantages of their own, but methods offering one target instead of two, and one eye to
observe instead of two, are without a doubt more dependable.
The value in this method does not lie in the gear, but rather the instructions on how to go about it.
The photo on the left shows the original Navy test fixture used with the Mk5 Collimator. The top of the fixture
allows the cylindrical piece of brass to be tightened down on hinges of various sizes. The telescope I’m looking
through (and over via the rhomboid prism attachment) is the “swinging barrel” (telescope) that can “swing” the
full range of IPDs. The other telescope is the “stationary” barrel. It is to be used as a STANDARD in the first part
of the process, even if it too has to be tweaked before the project is over. The photo on the right shows Cory Suddarth’s clamping set-up. It sits atop the original Navy X/Y stage with the right telescope upside down as shown in
both photos. Many binoculars today can’t be clamped with the original fixture. One telescope is still rigid while
the other is allowed to swing freely.
THE PROCEDURE
1. Place the binocular upside down on the test fixture. In 3-axis collimation it doesn’t matter which side is worse,
or if one side is aligned to near perfection. Unlike conditional alignment, this process is thorough, and results in
an instrument that is aligned at all IPD settings. Also, using only one eye, one does not have to worry about the
merging of images through inexperience, fatigue, or the inability to just stare, allowing the brain to do the work
of collimating.
It should be pointed out that the involuntary merging of images is what many people rely on when they say they
have “collimated” their binocular. I have tested many instruments that were “collimated” in the owner’s mind
when in fact a collimator revealed severe misalignment!
2. Move the right telescope (the left if the instrument were right side up) and bring it to the uppermost position
of the swing.
3. Use the X / Y stage to bring the reticle as seen through the binocular to the image seen over the top of the binocular using the auxiliary scope with the rhomboid attachment. This appears in the same telescope and allows the
reticles to be superimposed.
4. Gently swing the telescope all the way down and note the separation of the two reticles. You are trying to observe the distance between the line-of-sight as seen through the telescope vs. the line-of-sight seen over the top
of the telescope via the rhomboid attachment. It is not the end of the project if you’re heavy-handed, it just means
another cycle or two. Visualize where the center of a reticle—as seen through the instrument—would be if it were
exactly HALFWAY between the two.
5. Use the binocular’s adjusting screws or eccentric rings to move the image as seen through the instrument to the
position of the reticle you just saw in your mind’s eye.
6. You will notice you have only half the error you started with! Now, repeat steps 1 through 6.
7. Repeat as needed to get the two images to coincide. If you have to do the job more than 3 or 4 times, you aren’t
doing something correctly. When you think you have it, lower the telescope while looking through the auxiliary
scope. Watch the reticles stay together. This is not at all necessary, but will be great for your ego. You are doing
what others talk endlessly about but almost never do!
8. Now that you have aligned the swinging barrel (telescope) to the axle, it is time to work on the stationary barrel, aligning that reticle to the one in the swinging barrel—at any position along the swing. When you align to any
point on the swinging barrel, you align to all points along the swinging barrel!
Another thing that must be corrected before meaningful collimation can take place is the alleviation of “lean,”
also known as image tilt or image rotation, and often wrongfully addressed as “prism tilt,” which is a separate but
related condition.
Primarily found in Porro prism-based instruments, this condition can be seen when straight lines appear to tilt
from their actual planes. This is caused when the prisms, which are normally seated at 90-degree angles, are seated at some slightly different angle. Although rarely seen as a serious problem, or even noticed by some observers,
the image degrading effects of lean may be seen in binoculars which show no other signs of collimation error!
The fixture on the left is one of the U.S. Army’s
many obsolete testing fixtures (41-F-2987-547)
as referenced in their 1953 Ordinance Maintenance Manual TM 9-1580 TO 38-1-1. One can
easily see rigidity in such a device is of little
concern. Even so, the Army has allowed some
potential errors to arise for the sake of convenience. The whole set-up was about 3 1/2 feet
long, while the Navy Mk 5 required twice that
much space! Taking my lead from the opticalmen onboard USS Yosemite, I had my Mk5
mounted vertically on the wall, using a bathroom quality second-surface mirror to make it
convenient for a seated technician.
Finally Gang: I’m selling this because I’m still looking for work and money doesn’t grow on trees. But, I’m asking you all to remember where you read about this first. I know it’s ego, and I’m sorry, but since I have been writing articles, I’ve seen my research and observations all over the Internet, used as if it were original knowledge by
some who were optically clueless until reading some of my work. Thoughts on coatings; thoughts on zoom binos;
thoughts on glass manufacturing; thoughts on re-branding; and more. I’ve even seen some of my skewed phrases
used! Ego or not, I’ve been fighting against stiff odds—since the mid-70s—to get this concept understood and
accepted. Thus, I couldn’t bear to see some johnny-come-lately taking credit for my efforts. Hey, curmudgeons
are allowed egos too! —— Bill