Focusers in focus

The perfect focuser simply makes itself invisible. If it does not, you may need to help it a little.

You should not be aware of your focuser when using it. If you are, something is probably wrong.

First, you should familiarise yourself with the adjustment options. Especially with Crayford focusers, i.e. focusers that rely on the friction principle, you may be unsure which screw is the locking screw for locking the focuser and which screw regulates the pressure of the mechanism. The latter is usually located just above the axis of the focus knobs, the locking screw is generally closer to the telescope. Some focusers are adjustable along the optical axis. This is particularly important for rotating focusers.

If there is play on the Teflon-coated surfaces, you can carefully peel them off and glue adhesive tape underneath them. But it must not then sit too tightly. This minimises shifting – that is, the effect when the image shifts in the eyepiece while focusing.

Grease that solidifies in cold weather should be replaced, for example with lithium soap grease that does not damage plastic and is suitable for cold weather. For more sensitive focusing, a push-button micro-focuser can be retrofitted.

For DIY fans: black velvet self-adhesive film in the focuser tube is more effective than conventional matt paint. If the telescope end of the tube is unfinished, as cut during manufacture, this must also be taken care of. On the subject of cuts: you may find that the focuser tube protrudes into the optical path or reduces the telescope aperture. Then the optical path should be measured and shortened.

Author: Sven Wienstein / Licence: Oculum Verlag GmbH