Why can't I focus with Barlow?

[Dyptorden]

Hi,

I have an 8" Dob and I tried to watch Jupiter with my three eyepieces : 4mm, 17mm and 25mm. They work perfect.

Later I borrowed a friend's Barlow (the default plastic Celestron Barlow 3x he received with his Celestron Powerseeker 60EQ) but I can't focus at all no matter how low or high I moved the focuser when I used the 17 and the 25.

Any ideas why is this happening, and what can be done (what extra equipment I might need to obtain focus)?

[ronin]

Do you mean it gets sharper but runs out of travel before you get to the good focus position or it is blurry, half focused then blurry again?

If the second then would seem to be the barlow is no good at all.

If the first then you may need an extension tube to move the eyepiece back.

Alternatives are someone has been playing and taken the lens in the barlow out and put it back in wrong.

I assume that it can only go in one way and it is not the wrong way round.

[Lonestar70]

Hi,

I have an 8" Dob and I tried to watch Jupiter with my three eyepieces : 4mm, 17mm and 25mm. They work perfect.

Later I borrowed a friend's Barlow (the default plastic Celestron Barlow 3x he received with his Celestron Powerseeker 60EQ) but I can't focus at all no matter how low or high I moved the focuser when I used the 17 and the 25.

Any ideas why is this happening, and what can be done (what extra equipment I might need to obtain focus)?

Hi there,

A x3 barlow will move the focal point a good bit outside the focuser so you will probably need a short 1 1/2" or 2" (38mm or 50mm) extension between the barlow and your eyepiece... this will bring the focal point within the movement range of your focuser.

Hope this helps.

Sandy.

[John]

The barlows I've used generally moved the point of focus inwards a bit so you can run out of inwards focuser movement if it's a bit limited on your scope.

[Dyptorden]

I just made an experiment 2 minutes ago.

Took the 2"-1.25" adapter off and I kept this 3x barlow (1.25") with my bare hand, a bit deeper into the focuser.I obtained clear image.

What can I do so that I put the barlow deeper into the focuser? Any astro specific item to use? (I won't move the primary )

In few days my 4x Powermate 2" should arrive. Could I have the same problem with it?

[John]

Powermates tend to leave the focal position of an eyepiece where it is.

How are our answers matching those on "Cloudynights" ?

[Dyptorden]

usually a bit late but I am so glad receiving them I use this practice since long, due to the fact that there are ppl who only write in one of them.