I’m buying a secondhand telescope. What do I need to know?

BBC Sky at Night Magazine's Scope Doctor Steve Richards solves your astronomy ailments.

Celestron Advanced VX 700 Maksutov-Cassegrain telescope review

To get the most for my money, I’m considering buying a secondhand telescope. What should I consider before making a purchase?

Steve says: “Buying a secondhand telescope is a popular choice as astronomers generally respect their equipment to ensure they get the best out of it.

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But there are some safeguards that you can implement to further ensure that your purchase goes smoothly.

If the telescope has been used for astrophotography, ask the vendor to send you a recent photograph captured through the telescope and examine the star shapes closely, checking for any unwanted aberrations like astigmatism or flare.

Small marks on the outside of the optical tube are normal, but be very wary of dents as they’re an indication the instrument has been dropped.

Check the action of the focuser, ensuring that it is smooth with no flop in the focus tube. Examine the optics carefully under ordinary daylight, not with a torch.

General dust is quite normal, but look for any scratches or blemishes on the lens surface. If there are any signs of dust, moisture or fungal growth between any of the elements, walk away!”

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Email Steve your astronomy queries to contactus@skyatnightmagazine.com and they could be answered in a future issue of BBC Sky at Night Magazine.