DIY Table Top Binocular Collimator - The Experiment

I had already established the approximate distances between the components so I screwed the binocular support to the table such that the binocular objectives would be about 90cm (36”) from the collimator lens.

The collimation scope was fitted to its mount which was on the eyepiece side of the binoculars. As I had previously mentioned, the support for this scope had a base which fitted between the table laths and could mimic the collimator's movement from side to side.

Only the collimator had a fixed vertical height, the other two components in the layout could both have their heights adjusted.

The first stage was to ensure that the collimated light source was centred on the centre line of the binocular. To do this, I inserted the cardboard discs into the dew cap rings of the objective lenses and adjusted the collimator lens so that the image of the target was visible on the one disc.

It was easy to see if the cross wire centre was coincident with that of the disc centre and any discrepancies were easily rectified viz, horizontal difference slide the collimator in its guides, vertically; slacken the binocular mount locknut and move the binoculars up or down. It was also possible to slide the collimator to the other objective to confirm or otherwise that the second objective lens centre was also coincident with the collimated beam centre. The main reason why this would not be so would be that the binoculars were not level on their mount. Obviously any correction to this parameter would require the checking of the other objectives’ position until the two objectives were both centred on the centre of the light beam.

The next parameter to check was that the binoculars were square to the light beam i.e., they were not off-axis (tilted or skewed). This posed a problem as there was not a flat surface on the binocular body which I could use as a reference. I finally realised that the binocular dew cap rings were the only machined flat surface on the front end of the binoculars. I used this feature by securing a flat mirror over the objective lens, held flat against the dew cap ring with an elastic band stretched from the eyepiece end of the binoculars. The reflected light was then visible on the front wall of the collimator on which I had drawn a vertical and horizontal line with their intersection coincident with the lens centre. The lens was refocused. A perfectly squared binocular and hence mirror would superimpose the cross image onto the drawn lines. The arrangement was an optical lever very similar to that used in a ballistic galvanometer. The image was brought into alignment with the drawn cross by tilting and/or skewing the binocular mount. Once this was achieved, I removed the mirror and refocussed the lens so that I could check that the cross centre was still in the centre of the cardboard disc, any shift was corrected as previously described and the mirror replaced to check that squareness to the light beam had not been compromised.

Once this was satisfactorily achieved, the card discs were removed and the lens refocused once again but to the third position i.e., the one that produced the collimated beam. This was confirmed by looking into the binocular eyepiece.

That being so the spotter scope was slid into position, looking through the binocular eyepiece and the image of the cross wire studied through it.

I had set the distance between the spotter scope and the eyepiece of the binoculars such that the image from the eyepiece was slightly smaller than the view in the scope. This was so that I could ensure the scope was looking straight into the centre of the eyepiece-the image was surrounded by an annular dark ring.

Properly aligned binoculars would give an image of the cross wires of the spotting scope superimposed on the target image.

I had decided to correct any misalignment by adjusting the position of the objective lens within its eccentric retainer ring. To do this I had to unscrew and remove the dew cap ring. This I was able to do firstly on the right hand half of the binoculars. There was sufficient adjustment to attain the alignment of the two sets of cross wires. If there hadn’t had been enough I would have had to resort to prism adjustment.

I was also able to ensure the binoculars were still aligned to the collimator by repeating the operation with the mirror only this time the mirror was resting against the machined flat face of the binocular body and not the dew cap ring.

I then shifted the collimator to centre on the left-hand objective lens of the binoculars and moved the finder scope into position behind the eyepiece. The image in the left-hand half of the binoculars was coincident with the cross wire in the finder scope, so no adjustment was necessary in this case.

I could now remove the binoculars from their mount and look through them to see if the quality of the image had improved, which it had! The realignment process was a success.

INSTRUMENTS: Flat Double Sided Mirror

Precautions

Whilst I was checking the alignment with the mirror I leant on the table and saw the cross-wire shadow move on the front wall of the collimator by about ¼” the original position resumed as soon as I removed my weight. Don’t lean on the apparatus!

...and if you're listening Santa

..and now sit back and watch the film:

In Conclusion

I was pleased with the end results that I obtained by using this 'kitchen table' arrangement and once the initial 'teething problems' had been overcome, I found the apparatus easy to use. It would be interesting to develop an optical array that could produce two collimated images so that both sides of the binoculars could be tested simultaneously, obviating the need to move the collimator.

If you have enjoyed this article and found it interesting then share it with your friends on social media or suchlike. Please also feel free to ask questions and or make comments and if you found this helpful and would like to support this site you can always

Until next time and from a cold day in Normandie,

Cheers, Andy

© Andy Colley 2018

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Collimating WW2 Binoculars - A Cautionary Tale!

The first encounter I remember with my Uncle's WW2 binoculars, was at a family picnic out at an old RAF Aerodrome in Fradley, near Lichfield. These were always carried in his A35 van, in an open shelf-type compartment on the passenger's side. I never witnessed seeing them in any kind of case or cover.

WW2 Propaganda Poster

The other time I distinctly remember actually using them was at his home, when he asked me if I wanted to: "look at the tanks". With the vivid imagination of a 10 year old spurred on by the association of his time as a Desert Rat, I somehow expected to see something a lot more thrilling than the sewage containers at Bescot.

If you are wondering about these details, then it's because provenance is all with antiques and collectibles and if you know their history you can often come up with a (Sherlock) Holmsean solution to any problem. So, when I was reacquainted with these binoculars some 50 years later, I was disappointed that the view through them was not as clear as I remembered. The images through each side of the binocular were not in line and in fact they were pretty uncomfortable to use for anything more than a few seconds at a time. Seemingly, there was a collimation problem. As I have already collimated a pair of a more modern second-hand, Frank Nipole binoculars (article you can link to below), I did not see this as a problem.

In order to facilitate the collimation and also because it was a good idea anyway, I decided to make a clamp for the binoculars whereby I could attach them to my telescope tripod.

I used a plank from an untreated pallet and also a 'stringer' from the same.

Once the binoculars were mounted in the clamp, I oriented them so that I could look at a television aerial on a house roof some 80 to 100m away. It was very clear that the left-hand image was higher in the eyepiece than that of the right hand image and thus that adjustment was essential. Interestingly enough, vertical collimation errors in binoculars are the hardest for the human eye to compensate.

Unlike the other pair that I collimated (see above), the objective lenses, could not be easily rotated in their respective cells because of the design.  I was thus faced with the possibility that I would have to resort to prism adjustment and this I was loathe to do! It was at this point that I began to think of provenance, in that these binoculars which had been half way around the World, lugged across the desert and afterwards spent several decades travelling around in various vehicles without any protection before they ended in my mother's wardrobe, were incredibly clean. They also showed no signs of the external damage which are often associated with collimation. This lead me to believe that they had been cleaned on more than one occasion. I therefore wondered what the odds were that the objective lenses had been removed and mistakenly interchanged.

To test my hypothesis I set up the binoculars as if for collimation and initially began slowly to unscrew the left-hand objective lens. The images started to align. So, to determine by how much I would need to rotate the objective lens to achieve aligned images (collimation), I adhered one piece of electrical tape to the outside rim of the objective lens mount and another piece to the body of the binocular.

The collimation was achieved when the lens had been rotated almost three quarters of a turn. I could not imagine how I could fix the objective lens in this position so I continued with the premise that they had been interchanged and therefore, I unscrewed both objectives. On inspection of the inside of both I could see that the left-hand objective was more eccentrically mounted in its holder. The original collimation at time of manufacture had obviously necessitated this adjustment. Therefore, that adjustment meant that once the lens had been incorrectly swapped, the view through the binoculars would be compromised. This would not have mattered if both lenses were concentric in their respective cells.



This is a cautionary tale of a problem which I, with the advantage of having known the history of these binoculars, was able to think through before involving myself in a complicated prism adjustment. Therefore, if you purchase a pair of these World War binoculars, before you resort to any collimation do first consider that, this scenario is probably quite common!

If you have enjoyed this article and found it interesting then share it with your friends on social media or suchlike. Please also feel free to ask questions and or make comments.

Until next time and from a rainy day in Normandie,

Cheers, Andy

© Andy Colley 2018

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WW2 Poster Art Thanks to the Pinterest board of Historygallery.com