Focuser height for 2 inch focus lens, approximately 3.75 inch (95.3 mm) | Starlight

If the sharpest point of your homemade telescope is located outside the tube, you will need a significant increase. This 95.3 mm (approx. 3.75 inch) focal length zoom from Starlight Instruments places a 2 inch (approx. 5 inch) focal length zoom almost 10 cm away from the tube.

The increase is between the focus base and the focus. That is stronger than an extension tube in the extension tube, because that itself does not have to extend further. If you are building on a flat plate, then also look at the flat mounting base for 2 inch focusers.

Measure in advance how much extra range you need, because you lose just as much range inwards. Furthermore, with a Newton, the further the focuser of the tube is, the larger the viewfinder must be to fully illuminate the field of view. You can find more details in the telescope parts.

If this is too much, then there is The increase of about 2.75 inches.