Cleaning Celestron C90

[Bill-T]

Advice please. I have never had a mirrored telescope before and am wondering what maintenance is required. It's not sealed at the back so over time I expect some dust will get in just as it does in a camera lens. Does it affect performance significantly and how often and how should it be cleaned. 

[bosun21]

Ideally after a nights observing you should let the scope dry properly (if wet from dew) then a quick blow with the air blower on the front meniscus lens. You can then cap both ends to prevent any dust ingress. If stored in a shed or other outhouse then I recommend a dessicant cap for the visual back. This will protect the scope ensuring optimum performance.

[Chandra]

It is normal for dust to be on lenses and mirrors, and I would say it does not have a "noticeable" effect, unless the amount of dust and dirt is really large. The rule is to try not to "touch" the optical surfaces too much, no cotton pads, no chamois leather, nothing, unless it is absolutely necessary, so as not to damage the coatings. Blowing with an air bulb obliquely helps to remove dirt or coarser particles, there are special brushes with very soft bristles that help with this. 

If the optical surface is still very dirty, you should use specific solutions. Wet the special chamois leather and move radially from the center to the edge over the entire surface.

For mirrors, the best thing is distilled water with a couple of drops of dishwashing liquid, and clean it radially with a cotton pad. Rinse with distilled water and let dry in a vertical position.

Always wear latex gloves when handling lenses or mirrors to prevent skin oils from staining surfaces.

[Cosmic Geoff]

I have had the C90's larger brother, a 127mm Mak, for years, and have never attempted to clean it internally. It doesn't need it and anyway dismantling the scope is highly inadvisable.  As for the front meniscus,   I normally operate it with a dew shield, which keeps condensation off it, and the front surface very rarely needs cleaning (can't recall when I last touched it).