Prism Star Diagonal - Cant focus

Lo All,
I got a present of a Prism star diagonal for christmas. However when I have tried it I have never been able to focus properly on any object. Its almost as if it also changes the magnification.
Has anyone any ideas on what may be wrong?

Thanks in advance

Eoin

Eoin, can you give us any more details? Scope, eyepiece(s) you are using etc? Also, do you have a make/model for the diagonal?

Cheers
Dave

Lo All, I got a present of a Prism star diagonal for christmas. However when I have tried it I have never been able to focus properly on any object. Its almost as if it also changes the magnification.
Has anyone any ideas on what may be wrong?Thanks in advance
Eoin

Eoin,

Could be one of a few reasons ranging from damage or poor alignment to unsuitabilty. As Dave suggested, more information would be useful.

What star diagonal have you been using to date? Presumably your scope came with one if intended to be used with a star diagonal. If your scope came with a .965" diagonal, note that _some_ small refractors will not come to focus with a 1.25" hybrid diagonal (i.e. one that allows 1.25" eyepieces be used with a .965" focuser).

Can you achieve satisfactory focus on a distant object (at infinity) during the daytime when it's much easier to do so than at night? If so, leave it at that focused point and take out at night.

If not, perhaps the diagonal is out of alignment. Centre your eye on one end of the diagonal and look though it. Is the other end of the diagonal tube centred or misaligned? If the latter, it may be possible to loosen the screw or screws and tap the housing gently to try and reseat the prism. This may invalidate any warranty so I'm not advocating you do this if you intend referring back to the supplier.

You might also check if there is excessive side play between the diagonal tube and focusing tube due to poor machining. If so, you could be tilting the diagonal when locking it in place with the set screw.

Come back with more information and we'll see if we can offer further assistance.

Gordon

When you change over to using a diagonal (be it prism or mirror) it radically changes the focus position. This is not normally a problem on refractors or SCt/MCT. It is a major proglem in reflectors as there isnt enough focus travel in the focuser, most reflectors cannot use diagonals.
If you have a refractor, I'd bet the focus position with the diagonal is well up towards the tube.

If you wish you could bring the scope and diagonal along to the SAC meeting on the 11th Jan and we can have a good look at it and see whats going on.

I think you just answered my question there Dave. The scope is a reflector. Its an Atlas Explorer 1149 114mm Newtonian.

I'm afriad the diagonal has no make on it as it was bought from Ebay as a present.

I would love to come along to the SAC meeting but unfortunatley I'm on shift that night. Hopefully I will be around for the Feb one!!

Despite the problem with the diagonal I have been seeing some great sights in the skies.

Eoin