Remove dust from the mirror or lens on the inside surface

If there is dust on the mirror or lens on the inside, you can use a tube and a blower/compressor to remove it without removing the telescope.

To do this, measure the distance on the outside of the tube to avoid touching the glass surfaces with the tube. Now insert the tube through the focuser until just before the glass surface. The dust is then carefully removed with compressed air.

Afterward, the dust must be removed from the tube using a vacuum cleaner with a thin suction tube.

We always do this if we don't need to remove the lens cell. Otherwise, the lens cell is usually removed from the tube for adjustment and then the dust is blown away with a blower.

http://www.teleskop-spezialisten.de/shop/Ueber-uns:::12.html