Comet 6x24 binoculars from the inside – what went wrong?

28 September 2017
Marcin Górko

4. Prisms

My diagnostics of prism bodies started in a humorous way. Like in any real pair of binoculars I found a scale of interpupilary distance on the bridge of the Comet. The scale is very well-done, perfectly clear and visible; still you cannot read the actual distance at all. Why? Because the producer forgot to add an index ! It’s as if you produced a very good, accurate watch with a nice, clear face but you forgot about adding the hands… I understand cost-cutting practices but this time the producer went over the top!

Comet 6x24 binoculars from the inside – what went wrong? - Prisms
Half of the kingdom and a princess for a wife for anyone who manages to read the interpupilary distance value on this scale! The producer forgot (?) about the scale index, rendering it useless.

The mechanical aspects of the binoculars are visible after unscrewing slides of eyepieces, slides of objectives, and disassembling four metal protective plates. Each of them is attached to the binoculars’ body by one screw. If the producer used two or three screws like plenty of renowned manufacturers, that plate would fit the prisms better, without any slits and dust wouldn’t invade the interior of the binoculars.

Now about blackening or rather lack of it. If in the eyepieces part the situation was bad, in the part with objective lenses it is really abysmal!

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Comet 6x24 binoculars from the inside – what went wrong? - Prisms
Interior of the prism body from the side of the eyepiece. Raw aluminum was properly blackened, the metal plate keeping the prism in place was glued using nail polish…

You get large areas of bright, shiny, raw aluminum. If I were nasty I would say the producer of the Comet should think about entering the wheel rim market where shiny surfaces are much more appreciated. Fortunately I am far from nasty – in order to improve image contrast every visible aluminum surface I blackened as well as I could. Now back to the prisms: once again classic solutions were employed in this device. Prisms are pressed to the casing with a help of a springy plate. Unfortunately both sides of that plate are just pushed in so only the force of friction keeps them in their proper position. No glue, no screws – it means that if the binoculars, during its hopefully long life, is exposed to shocks and vibrations there is great possibility that the plate will get loose and, after that, the days of proper prisms collimation are numbered. All four plates I fixed in their places with nail polish. To make everything clear I would like to add the polish belonged to my wife …

Comet 6x24 binoculars from the inside – what went wrong? - Prisms
The producer must find whitening toothpaste fascinating. Never in my life had I seen more bright binoculars prism body. After blackening the situation returns to normal.

The collimation issue proved to be another surprise. It’s been known that in case of small binoculars the collimation of optical paths is achieved by eccentric objective lens mounts. In big sets of binoculars (80 mm and more) the objectives usually don’t move so the collimation is done with the help of small screws responsible for the inclination of prisms - one screw for every optical path is enough. Meanwhile our ‘comet’ – as it sometimes happens with comets and such – surprised me even twice in that area.

Comet 6x24 binoculars from the inside – what went wrong? - Prisms
The producer put as many as four screws for prism collimation inside (two would be quite enough!) but none of them is available unless you want to damage the binoculars!

Firstly – despite small dimensions it offers prism collimation; secondly, there are as many as four collimation screws, one for every prism. Still you can find out that much only after removing the eyepieces and the objective lenses because the screws are hidden under the leatherette armour. Fortunately the armour was not glued in place very well so, after removing it, I had access to the screws adjusting eyepiece prisms. Of course bear in mind that another set of binoculars might be a bit more difficult to regulate; perhaps you’ll have to tear the leatherette off or make a hole in it… Now about the prisms: they are glued to the body and here you encounter another surprise. One of eyepiece prisms is fixed in place very neatly but with gray glue; another one is fixed with black glue, a far better option, but not especially well.

Comet 6x24 binoculars from the inside – what went wrong? - Prisms
Look hard and find two differences in prisms fixing. A tip: they did a neat work but used gray glue in the first case and splashed black glue shoddily in the case of the second…