Does it need servicing?

Quite often the user of an optical instrument does not realise that it will benefit from being serviced. Repair of an instrument is obviously needed when it is broken but there are other cases, less obvious, when an instrument needs servicing and the following are a few notes on such cases. These notes apply to optical instruments in general, including binoculars, telescopes, ophthalmic instruments, riflescopes, etc.

Insidious effects over time cause the performance of an instrument to fall off very gradually due to reducing light transmission. A build-up of dirt and dust is the most obvious cause but, even in a well-sealed instrument, a reduction of performance can be caused by fogging, filming, rust and fungus and a few words about these may be enlightening.

If moisture enters the instrument, it will cause fogging and, for outdoor instruments such as binoculars, this will be especially noticeable at dawn. Even a well-sealed instrument may have some humidity trapped inside if its air is not thoroughly desiccated before sealing. Specks of dust can act as centres around which condensation can collect.

Filming of optics is not dependant on humidity but is caused by the action of atmospheric gases on the glass surfaces, progressively reducing light transmission. Another cause of light reduction is rust or dew-like films on the optics caused by minute droplets which leave a grey coating of alkaline salts. These gradually produce a grey film on the glass.

All of the above effects can be avoided or virtually avoided by, in the case of sealed instruments, purging and filling with inert, oxygen-free nitrogen. This process was first introduced in 1971 by the Steiner company and is carried out by Optrep after an overhaul. Prior to the use of nitrogen, instruments were placed in a desiccator in a partial vacuum to remove any humid air and this was then replaced with dry air. In some processes, silica gel was used.

Another cause of filming, not dependant on the atmosphere, is the outgassing of volatile constituents from grease lubricants and sealants. Also, an aluminium alloy body or the mechanical parts can deposit oxide and oil distillate on the optics. Oil can be taken up by aluminium alloy during the machining process.

A particular menace to optical instruments is fungus. This is a living, microscopic plant, similar to mildew and mould, and is reproduced by spores. Spores enter an instrument in the air and they can thrive on dust, finger prints, cloth fibres, sealant compounds, lubricant, cork and paint. Favourable conditions for spores include a relative humidity in excess of 70% and so, once again, filling a sealed instrument with nitrogen to exclude all moisture is a very good practice. If fungus has been present, Optrep carefully use heat and/or fungicide to kill off the spores but the exclusion of moisture and food for the spores as far as possible is most important since some spores are likely to be trapped inside the instrument during reassembly.

The greatest care is taken during the overhaul of an instrument at Optrep. Dust is avoided or minimised with special techniques and cork is replaced with nitrile. Fresh cleaning cloths and materials are used for each instrument (to avoid transferring any spores), skin acids are kept from internal surfaces and sealants and lubricants are not left exposed to dust.

On the mechanical side, a stiff or inaccurate mechanism can be caused by damage, dirt or grit or by ageing lubricant and repair or servicing is clearly needed. Never be tempted to oil an instrument since this will only result in a bigger repair bill later on.

Optical misalignment, due to a fall or a blow, will have various bad effects including lack of or only partial focus, inaccurate readings and, in the case of a binocular instrument, double vision. It will be better if an instrument is grossly misaligned because then it will not be used until it has been repaired. If, however, it is only slightly misaligned, the user may continue to use it and thereby obtain poor results. In the case of a slightly misaligned binocular instrument, for example, the user’s eye muscles will tend to compensate for the optical misalignment with a headache or nausea being the end result.

All the above problems and many more can be solved at a good optical repair centre but, these days, such centres are few and far between. All too often evidence of poor work or damage from amateurism is to be found. This is commonly hidden inside an instrument and includes damaged screws, misfitted or damaged seals, failure to relubricate, failure to diagnose and correct the original fault and a failure to render the optics immaculately clean. Even more obvious is when an instrument has not been adjusted or collimated exactly. Such treatment of precision optical instruments is enough to make a skilled optical technician weep and shows a lack of appreciation of the instrument and a lack of pride in one’s work. No such problems exist at Optrep where taking a pride in producing the best possible work is fundamental to out ethos and dates back to 1960. Regular servicing of an instrument not only keeps it in good condition but also extends its life and avoids breakdown or more expensive work later on. Does your instrument need servicing?

© A.L.Kay