Extending the length of a flex tube dob

[Phil4130]

I own a Skywatcher 250 Flex Tube and was wondering what effects it would have on the performance of the scope hypothetically if you were to extend the flex tube poles and therefore the focal length???

[pvaz]

I own a Skywatcher 250 Flex Tube and was wondering what effects it would have on the performance of the scope hypothetically if you were to extend the flex tube poles and therefore the focal length???

The primary mirror parabolic shape is precisely made to produce a light cone with a specific length. Extending the tube will mean the focuser will be outside the focusing spot so nothing will focus. You'll need a new primary mirror designed for the new focal length.