My rich field short tube refractor will not focus

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I’m writing this brief guide, as this is a common problem encountered by those who are unfamiliar with rich field/short tube refractors…

In all but very rare cases this is not a defect in the scope at all and is encountered even in the most expensive telescopes of this type. The reason is that most telescopes of this type are designed for use with a star diagonal for visual observation.

The star diagonal serves two purposes on these scopes.

Firstly it enables more comfortable observation of objects high in the sky or even overhead.

And secondly, it effectively extends the focusers drawtube allowing focus to be achieved with standard eyepieces.

If you purchase a rich field short tube refractor as part of a kit, then a diagonal will normally be included along with at least one eyepiece.

However, if you bought the telescope as an OTA (optical tube assembly) then unless stated in the advertisement you should assume it will not include a diagonal or other accessories. This helps keep the cost down, as many of those who buy an OTA will already have a suitable mount, diagonal and accessories.

As a rule of thumb, most astronomical refractors will require a star diagonal for comfortable viewing. If you do not already have one then ask the seller whether it is included/required or if they are able to provide one. If they are a dealer they may be able to provide it at a lower cost and postage free if you ask prior to purchase.

Finally, if you bought your scope new from a dealer and you suspect a problem then please do not be tempted to dismantle it yourself as this will void any warrenty. Instead, contact the dealer for advise and if necessary they will ask you to return it for repair/replacement. Without specialist knowledge and or equipment it is extremely difficult to correctly realign the lenses in a refractor once removed from their cell.

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