Vertical collimation

[SpaceBass]

I recently came across this article on the Oberwerk website about vertical collimation.  So I tested out my six pairs of binoculars and found that two- Kowa YF 6X30 and Pentax Papillo II 6.5X21- were out.  I'm unable to photograph it but it looks the same as in the article.  

So just wondering how much an issue this is compared to regular collimation?  

 

Quote

To check vertical collimation, look at a distinct horizontal line, such as a roof line, gutter, or fence rail. Slowly move your eyes back from the binocular until they are about 3 inches away, while maintaining the view of the horizontal line in eyepieces. Let your eyes relax and focus more on the image at the eyepieces rather than through the binocular. Even a slight vertical miscollimation will now be readily shown as a difference in position of the horizonal line

https://oberwerk.com/collimation-instructionsfor-lw-series-and-mariner-series/

 

 

 

[BinocularSky]

There's no such thing as "regular collimation"; collimation is binary: binoculars are either collimated or they aren't. Binocular collimation is a process by which the optical exes are made parallel to each other and to the binocular's hinge - anything else is miscollimation. Miscollimation can be in any direction; any vertical component is called "step" or "dipvergence"; any horizontal component is called "convergence" (your eyes converge to try to unite the  images) and "divergence" (the opposite). You rarely get one without the other.

(NB: There are two conventions for which is called which in horizontal misalignment;  "eyes converging" is the one I prefer to use for convergence; "binocular axes converging" is the other.)

You can handle quite a lot of convergence (our eyes naturally do this when we look at something close), and very little step. Approximate tolerances in the apparent field of view are:
Step: 15 arcmin
Horizontal Convergence: 45 arcmin
Horizontal Divergence: 20 arcmin

Divide these by the magnification to get the actual tolerance.

In the image shown in your link to the Oberwerk site, the collimating screw moves the image diagonally, so it will affect both step and convergence/divergence.

The article also mistakenly says that it's easier to collimate in daytime; it isn't (unless you are doing it on an optical bench, which most of us aren't). Your visual system tries to adjust for any miscollimation, so you need to fool it by making it "think" that each eye is actually seeing something different. Common ways with a star are:
* Defocusing one side: you collimate to put the focused point in the middle of the unfocused blob.
* Use anaglyph glasses (or coloured cellophane sweet wrappers) so the image are different colours; merge them
* Used crossed Bahtinov masks (one horizontal, one vertical) and merge the diffraction patterns.

The Bahtinov method is most precise, but it is more precise than it needs to be; the defocusing method is usually adequate. However, note that none of this (or anything on the Oberwerk page) will guarantee you true collimation, because it ignores the axis of the binocular's hinge so, if you change the IPD, the optical axes will probably no longer align.

That's probably far more than you wanted to know... 🙂
 

Edited June 2, 2020 by BinocularSky

[SpaceBass]

@BinocularSky

thanks for the excellent summary!  I believe the two binos in question look the same with a defocused star (by diopter adjustment) as do the other ones I have.  All six of them have the focused point just inside the unfocused blob, usually top half and right side position. Does this mean that I can discount the Oberwerk article with those two, then? 

As regards the focused point not being more towards the centre of the blob, if all six pairs show the same postion, I suppose it's more likely due to my eyes being a bit crossed than an indication of slight miscollimation.  As discussed on CN a while back:

https://www.cloudynights.com/topic/460672-checking-collimation/

 

 

 

 

 

 

Edited June 3, 2020 by SpaceBass

[BinocularSky]

 If you think that your eyes might be "out", just try the binoculars upside down; that should tell you. 🙂

[SpaceBass]

Sorry, not quite with you on that.. I haven't any idea whether my eyes are out or not, just that I've observed almost the same near edge postion with many binoculars, both past and present.  It seems 'unlikely' that the whole lot were miscollimated. 

Anyhow, your informative previous post would seem to suggest that the oberwerk article is not to be taken seriously and that all my binoculars are pretty much collimated (albeit not accurately measured) including those two.  Thanks for your help, much appreciated.

Edited June 5, 2020 by SpaceBass