Barlow oddity - Fordos attempts most ridiculous question award again!

[Fordos Moon]

Okay so I tried and tried to get the Celestron ED 2x Barlow I picked up to work, without success.

Jupiter was in my sights and it looked good at 1am through the SW 10mm ep but I thought I'd try the Barlow.

I put it between the scope and the ep but all I could see through the ep was the scope primary mirror with the secondary mirror's silhouette on it.

Now as Kylie said I know I'm doing something stupid but I can't fathom it out!

Will happily be ridiculed to find an answer!

[jimmyjamjoejoe]

Sounds silly, but are you aware you need to refocus after putting the barlow in? The image of the secondary shadow only becomes apparent when either way out of focus, or maybe faintly if the exit pupil is way too big. Given the EP, i doubt it's the exit pupil...

[Fordos Moon]

Yep Jimmy I did, but still couldn't see anything but the mirrors :-(

[Rihard]

Okay so I tried and tried to get the Celestron ED 2x Barlow I picked up to work, without success.

Jupiter was in my sights and it looked good at 1am through the SW 10mm ep but I thought I'd try the Barlow.

I put it between the scope and the ep but all I could see through the ep was the scope primary mirror with the secondary mirror's silhouette on it.

Now as Kylie said I know I'm doing something stupid but I can't fathom it out!

Will happily be ridiculed to find an answer!

I've experienced this before even with my 114" scope. That looks like a focus problem.

Try to go all the way out with the focuser, and also all the way in. Sometimes (at least with my 200P) it might feel that you reached the limit because the focuser feels sort of "stiff" at some point, maybe because a screw on the bottom is too tight, but be aware you might be able to go further out (or in) and improve the focus.

Also make sure that the barlow is completely inserted inside the focuser and that the eyepiece is also correctly inserted inside the barlow. Or else, is the barlow missing any piece of glass? :grin:

A barlow I used to use with my old Konus 114 had an element that could be extracted to be fitted backwards in the main barrel, however it would not work this way. I don't know if your Cel' barlow works that way as my old barlow, but if this part can be extracted, you may want to make sure that it is fitted into the main barlow barrel the right way and not backwards.

Consider trying all this during the day to see if you achieve focus, maybe focusing on a far roof or tree.

Hope this helps (and hope it makes sense )

Clear Skies

[Fordos Moon]

Thanks for the response! Will test it out in daylight :-)

[Astro Imp]

Might seem pretty obvious but when you focus with the Barlow the point of focus is really small so move the focuser as slowly as you can.

[Fordos Moon]

Thanks Imp will do when a clear sky eventually arrives

[Cornelius Varley]

The barlow lens would move the point of focus further out and this may be beyond the range of the focuser drawtube. You might need a short extension tube to give you a bit more length.