Refractor focus point

[D Wright]

Bit of a dumb question but I just can't grt my head around it. I have a cheap 70/400mm refractor and I can only get focus using a diagonal. I want to use it as a guide scope so will need focus without the diagonal. I am planning to replace the main tube, so will I have to increase the length of the tube to get correct focus?

[Alien 13]

A diagonal will add about two inches to the light path so if you want to focus without one you will need a two inch extension piece.

Alan

[D Wright]

I want to avoid using an extension as the focuser is a long way out already and is not very good so the further in it is the more stable it will be.

[D4N]

If you use an extension tube the focuser will be further in.

[ecuador]

You probably have something like a Travel Scope 70? Weak focuser that you don't want to stress much? The solution is to use a 1.25" reducer. It will make the scope faster (great for guiding) and will bring the focus point closer so you won't need an extension.

[ecuador]

Example 1.25" reducer that I've tried: https://www.amazon.co.uk/Solomark-Photo-Visual-Reducer-Eyepieces-Nosepieces/dp/B016AN6HPM/

It is 0.5x at about 2.5cm from the sensor, less reduction (and less moving of the focal point) when closer, more when farther so you can tweak.

That review below the Amazon listing is actually mine