DIY Table Top Binocular Collimator - Sourcing Materials & Fabrication

My first experience of re-aligning the optics in an old pair of binoculars although successful relied heavily on a subjective assessment of how the images could be brought into alignment by altering the optical path through the binocular’s objective lens. I was intrigued by how a ‘scientific’ method could produce a more satisfactory result.

To this end I decided to make a collimating setup similar to that described in the book by Seyfried.

The advantage of this method is that the whole operation can be undertaken indoors and within the confines of a table measuring less than six feet by three feet.

The arrangement comprised:

• table top
• collimator
• binocular mount
• collimating scope

On reading of the materials necessary to build this apparatus, I realised that I had all the items in my workshop all I had to do was put them together. However, I have provided some links to sources for tools and equipment, which I hope will prove useful.

Here also is the link to the book, It is out of print but you can still find it:  'Choosing, Using and Repairing Binoculars' by J.W. Seyfried' is the link for the UK.

Here is the US Link: 'Choosing, Using and Repairing Binoculars' by J.W. Seyfried'
 

Once I got down to the construction, however, I realised that there were several potential problems with the layout. When I checked online for information and/or to see if anyone else had undertaken the experiment, I could find no evidence that it had been attempted. With our kitchen table out of action and us having to cook and prepare meals around the set up, this was going to be an interesting challenge on many levels. 

COMPONENTS:  

Table Top 

Both the collimator and the collimating scope needed to move laterally so that the light could be directed through each half of the binocular and the effect observed. On a workbench I would have screwed horizontal rails to the top of the bench to hold the pedestal base of each of the components so that they could be moved parallel to each other. As I was using the kitchen table, I decided to place on top of it a trestle table top I made some years ago from pallet wood. This I placed upside down on the kitchen table as the pallet wood planks were nailed to four laths that would suffice as the guide rails.


It is important to note that I estimated a practicable height for the binocular support and used it as the required heights for the centre lines of the collimating scope and the collimator. 

Collimator.

The most important part of this kit is the means by which an object appears to the binocular to be at ‘infinity’. A collimator is such a device; a cross-hair reticle is illuminated using a low wattage light bulb. A lens placed on the other side of the reticle at its focal length will make the light beam parallel. To the binocular, the parallel light path appears to come from a great distance and hence its optical elements will bring to focus in the eyepiece an image of the reticle.

My light box for the collimator was made from thin (½”) pallet wood. My light source was an old garage inspection lamp from which I had removed the bulb protection cage. This cage was attached to the plastic body of the lamp with a metal threaded collar. I attached the collar to the inside rim of the hole I had cut in the end wall of the box using a Jigsaw with three short screws and could then screw the lamp body into it. However, a bulb holder screwed to the rear wall of the box would suffice. I used an LED 6000K Bulb

The reticle housing was of the same wood as the rest of the box, cut to fit the interior width of the box with enough clearance on the width for it to be moved towards and away from the light.. A circular hole was cut centrally within this. I made the reticle from thin copper wire held in place by four screws – I wound the ends of the two pieces of wire around the screws. After the initial observations of this reticle through the rest of the equipment, I realised that the cross wires could not be simultaneously brought into focus due to my being unable to wind the wires tightly enough around the screws. I changed this by soldering the two wires together at their point of intersection and then used a glue gun to secure the other ends to the support frame whilst keeping each wire under tension.

The exit hole cut in the end wall was made to fit a magnifying glass I had in my workshop. I subsequently replaced this lens with a smaller, less powerful lens due to some infuriating problems when trying to set up the apparatus. The moveable reticle housing was fixed at a distance equal to the focal length of the lens.

The lightbox was screwed to two supports set at a distance to rest against the inside vertical faces of the laths on the underside (now uppermost) face of the table top so that the collimator could be moved to align with either of the binocular objectives. The photograph above shows the lightbox after certain necessary modifications had taken place and these are discussed in the next article. This was a real 'thinking-on-your-feet' experiment and I didn't always remember to take images of each stage!

TOOLS: Jigsaw, Glue Gun, Soldering Iron, Screwdriver and Hand Saw
EQUIPMENT: Optical Glass Lens

Collimating Scope

Being an amateur astronomer I had to hand a 6x30 finder scope from my telescope. This has within its lens system a cross-hair reticle ideal for aligning with the target cross wires in the collimator. Alternatives to this would be a budget-priced telescopic sight for a rifle.

I made a support for the scope from pallet wood. I’d read that the alignment method should take into account the changes that arise when the the interpupillary distance (ipd) is altered i.e., when the binoculars are at the extremes of their movement on the central hinge. A change in the ipd would result in a change in the vertical position of the optical axis of the binoculars, thus I needed to make the height of the scope above the table adjustable. This I did by supporting the scopes’ mounting plinth on three 10mm threaded rods. Vertical movement was effected by screwing the nuts beneath the plinth up or down.

EQUIPMENT: Finder scope or Rifle scope

Binocular Mount

The binoculars under assessment needed to be rigidly attached to the worktable top at a height adequate for allowing access for adjustment either of the prisms or the objective lenses. The mount would also have to allow the ipd to be adjusted from maximum to minimum.

I chose to attach the support to the binoculars using the threaded hole in the binoculars' hinge, this is normally used for attaching the binoculars to a tripod. I had in my ‘optical bits and bobs’ a spotter scope tripod mounting bracket made by Vanguard (model ref QT-30) and this I secured to a wooden support via two ¼” (6mm) bolts. This would give me approximately ±1½” (±35mm) vertical movement, more than enough to accommodate the change in objective centre line height when the interpupillary distance is altered.



EQUIPMENT: Vanguard QT-30 Tripod Mount or there are cheaper Binocular Tripod Adapters but they will need to be fitted to a vertically adjustable mount.

In the next article we look at the modifications needed to make this work.

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Until next time and from a cold day in Normandie,

Cheers, Andy

© Andy Colley 2018

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