Maintenance
Telescope Maintenance: What to Do, and What to Leave Alone
Most telescope maintenance advice is about what not to do. Over-cleaning optics causes far more damage in India than dust ever does.
The most useful thing to know about telescope maintenance is how little of it there is, and how much damage is caused by doing too much. Dust on a mirror costs you a fraction of a percent of light. A scratch from over-enthusiastic cleaning is permanent.
The rule about cleaning optics
Do not clean your optics. Not until you genuinely have to.
A primary mirror with a visible film of dust loses only a small amount of light and contrast — well under one percent for light dust, and rarely more than a few percent even when it looks dirty. Nobody has ever noticed that difference at the eyepiece.
A scratch, a smear of residue or a stripped coating is permanent and does far more harm.
The realistic schedule for a mirror in Indian conditions is a proper clean every three to five years, and only when performance has visibly degraded. Front lenses on refractors are sealed and essentially never need it.
Eyepieces are the exception. They collect eyelash oil and skin contact, which does affect the view. Clean the eye lens when you can see marks on it — a puff of air first, then a lens-cleaning solution on a fresh microfibre cloth or lens tissue, wiped gently in one direction. Never dry-wipe an optical surface, as that grinds dust into the coating.
Dew, which in India is the real enemy
Dew forms when the telescope's surfaces radiate heat to the sky and drop below the dew point. It appears on the corrector plate of a Schmidt-Cassegrain, on the front lens of a refractor and on the secondary mirror of a Newtonian, and it ends the session.
A dew shield is the standard prevention. An extension of the tube past the front optical surface reduces its view of the cold sky and delays dew formation substantially. Commercial ones exist; a rolled sheet of camping mat secured with Velcro works about as well.
Dew heaters are low-power resistive strips that keep the surface a degree or two above ambient. On a humid coastal night they are the only reliable answer.
Never wipe dew off optics. Wiping drags whatever dust is present across the coating. Let it evaporate, or use a gentle hairdryer on a cool setting held well back.
Crucially: never store a telescope while it is damp. Leave it uncapped indoors for a few hours to dry fully before putting caps on and storing it. Sealing moisture inside a tube is how fungus starts.
Fungus, the specifically Indian problem
In humid conditions, fungus can grow on optical coatings — a branching web that etches the coating permanently. It is a genuine risk in coastal and monsoon-prone regions, and it is the single most serious threat to a telescope in India.
Prevention is straightforward:
- Store the telescope somewhere dry and ventilated, never a sealed damp cupboard
- Put silica gel packets in the eyepiece case and near the tube, and dry them out periodically
- Always allow the telescope to dry completely before capping and storing
- Use the telescope regularly — instruments left sealed for months are the ones that develop problems
Collimation for reflectors
Collimation is aligning the mirrors so the light path is centred. It is not maintenance in the sense of upkeep — it is a routine adjustment, like tuning a guitar.
Check it whenever the telescope has been transported roughly, and occasionally otherwise. A collimation cap costs very little and is sufficient for visual observing; a laser collimator is faster but needs to be collimated itself to be trusted.
The star test is the practical check: point at a moderately bright star, defocus slightly, and look at the resulting disc. It should be a set of concentric circles. If the central shadow is off to one side, collimation needs adjusting.
Mechanical care
Do not over-tighten anything. Plastic threads on entry-level mounts strip easily, and a stripped altitude lock is a much bigger problem than a slightly loose one.
Keep the focuser clean but not lubricated. Dust in a rack-and-pinion focuser causes roughness. Wipe the visible rack occasionally. Do not add oil — it collects dust and makes things worse.
Check bolts periodically. Vibration loosens tripod and mount bolts over time, and a loose bolt is a common cause of unexplained wobble.
Store the tube horizontally or vertically, not resting on the focuser. And keep dust caps on when it is stored, off when it is drying.
Batteries and electronics
For GoTo mounts, remove the batteries if the telescope will be unused for more than a few weeks — leaked alkaline cells destroy battery compartments and this is a common, avoidable failure.
A rechargeable power pack is better than internal batteries in almost every respect: longer runtime, more stable voltage, and no leak risk. Voltage sag from tired batteries causes erratic slewing that is often misdiagnosed as a mount fault.
An annual routine
Once a year, ideally before the good observing season:
- Inspect optics in bright light for fungus, coating damage or heavy contamination
- Check and adjust collimation
- Tighten every bolt on mount and tripod, without over-tightening
- Clean eyepiece surfaces properly
- Replace or dry out silica gel packets
- Check batteries and cables on electronic mounts
- Take the telescope out and star test it
That is the whole job. Everything else is best left alone.
