Barlow lens. Again

[filwud]

I have bought 8" skywatcher dobsonian, it has 2" extension, I assume Barlow, but when I try to use it on moon, it's just a bright white unfocusable blob, I have two lenses, both same, works fine without Barlow. I'm at a loss how this works, I can't see any other way of using them

[John]

The 2 inch extension is the adapter for 2 inch eyepieces, not a barlow lens.

If you use it and the 1.25 inch adapter together (like your top and bottom photos) you get just the problem that you have experienced with the 1.25 inch eyepieces - they won't come to focus. Use just the 1.25 inch adapter on it's own (your middle photo) and you should be fine.

 

Edited August 30, 2023 by John

[filwud]

Ah ok, thank you, the instructions explain using the Barlow lens and I just assumed that was it, I'll just stick to supplied lenses for now

[Louis D]

You can identify a Barlow lens by it having an eyepiece holder at one end with a setscrew and a lens at the other end that inserts in the focuser.

[Mandy D]

12 hours ago, Louis D said:

You can identify a Barlow lens by it having an eyepiece holder at one end with a setscrew and a lens at the other end that inserts in the focuser.

Unless it's a focal extender!

It still does a similar job, only better.

[Louis D]

9 hours ago, Mandy D said:

Unless it's a focal extender!

It still does a similar job, only better.

Or a 1.25" Tele Vue Paracorr.  But they're so rare, I didn't think it worth mentioning.

All this assumes 1.25"-only.