Telescope Reviews: Binocular Collimation

Binocular Collimation

In more than three years on Cloudy Nights, I have never proposed to write an official “article” for the group. However, I am incessantly reminded that there are many misconceptions concerning collimation that just keep cropping up which are as wrong today as they were when they were conceived, and I would like to add my two cents worth to the subject.

1) The word “perfect” and “collimation” do not belong in the same sentence.

2) Alignment that is within the original JTII standards can be considered to function as “perfect” in that the eyes can easily accommodate the error without introducing noticeable eyestrain. For example, an 8 power instrument should have errors equal to or less than 4’ Step, 10’ Divergence and 6’ convergence, with a 16 power having 2’, 6’ and 3’ respectively.

3) Some people profess to able to “eyeball” collimation. A few of us can get within industry standards at a GIVEN IPD. This has been accepted as being called “conditional alignment” where the alignment is based on the performance of the instrument at one, AND ONLY ONE, IPD (Interpupillary Distance). HOWEVER, we can’t do it all the time based on a number of varying biological conditions. And, if you can’t duplicate human performance, the validity of the test must be called into question.

Two or three times a day, I see people who say their binocular is “perfect,” “just fine,” “good enough for me,” or the like when, in fact, it might deviate from maximum allowable error by THREE OR MORE DEGREES—not minutes, DEGREES! Are they really seeing fine? Perhaps. BUT, if they are, they are causing eyestrain. Old wives tales notwithstanding, you can’t have it both ways.

4) Collimation is collimation is collimation. A binocular is either collimated or it is not. Some folks talk about the collimation of the “tubes” or “barrels” as if that condition is somehow separate from the alignment of the optical system. While it does give folks something to talk about (and worry about) it has little to do with collimation. It would only be important IF THE TUBES WERE OUT OF ALIGNMENT WITH THE AXLE SO MUCH THAT COLLIMATION CONVENTIONS—ECCENTRIC RINGS OR SET SCREWS--WOULD NOT HAVE ENOUGH MOTION TO BRING THE INSTRUMENT INTO ALIGNMENT. If you could find a way to have one telescope pointed toward Texas and the other pointed at London, with the optics themselves being collimated, then the BINOCULAR would be collimated.

5) Some people profess that they can tell whether a binocular in collimated by looking through it backwards—one scope at a time. In a sense this is correct. However, it will usually produce useless information. If the binocular is so far out of alignment that it can be seen with this method, it is far enough out to be seen looking through it correctly.

This method may be easily used to see which telescope (meaning the optical train) is out of alignment the most. Thus, if one is planning to perform only a conditional alignment, it would be a good place to start. REMEMBER: for a given IPD, conditional alignment is the same as “collimation.”

Then what is the difference?

CONDITIONAL ALIGNMENT can be eyeballed by most people under varying conditions as long as alignment at one IPD is all that’s required.

COLLIMATION: In true collimation, alignment is within a prescribed minimum standard at ALL IPD settings. In this realm, there is no security in numbers; if 500 people talk about how they have just collimated their binoculars, then 500 people are wrong. I could certainly agree they have aligned the instrument to make it acceptable for themselves, but “collimated” . . . no.

6) Finally, many people try to help newbies figure out whether or not their binoculars are aligned by asking them to see if they notice that they have overlapping fields of view or “overlapping circles.” Well, this is only PARTIALLY correct and as often as not causes people to worry about their binoculars, or, worse than that, causes them to start tweaking with an instrument that are already within industry standards for collimation.

If one is looking at a distant OBJECT and notices—with peripheral vision—that the fields overlap, then a collimation error is present.

More often than not, the uninitiated will LOOK for collimation error by concentrating on the “circles.” When they do this, they are focusing INSIDE the binocular. And what happens when you focus on something that close? You have to cross your eyes. And what happens when you cross your eyes? You start seeing double? And what do you THINK is wrong when you start seeing double? You think the binocular is out of alignment . . . when, in fact, YOU are!

Cheers,

Bill

Edited by EdZ (11/05/07 03:09 PM)