What type of newtonian do I have

[tony.673]

I have a cheap newt that I haven't used for a few years and would like to bring it back into service but I don't know what type it is. Everything looks like a normal newt but the focuser incorporates a lens at the tube end. I've always had trouble collimating, a laser collimator won't work if the lens is in place. If I knew exactly what type it is I could google for details. Any help?

Tony

[Cornelius Varley]

10 minutes ago, tony.673 said:

I have a cheap newt that I haven't used for a few years and would like to bring it back into service but I don't know what type it is. Everything looks like a normal newt but the focuser incorporates a lens at the tube end. I've always had trouble collimating, a laser collimator won't work if the lens is in place. If I knew exactly what type it is I could google for details. Any help?

Tony

This type of telescope is known as a Jones-Bird or barlowed reflector. The lens within the focuser corrects spherical aberration from the spherical primary mirror as increases the focal length. And you are right, this type of telescope can't be collimated using a laser.

[billyharris72]

That'll be a Bird-Jones design. The bad news is that while not an inherently bad design, they're not easy or cheap to make well, and the only ones out there seem to the cheaper ones. 

They're inherently quite hard to collimate also, as the lens element makes using a laser or a Cheshire impossible. I suspect your best bet might be to try collimating on a star, though that could be tricky if it is significantly out.

I've seen that there are a couple of videos on YouTube about this and hopefully one will help. A pretty much universal piece of advice on forums is not to be tempted to remove the lens - putting it back in will throw the collimation out again.

Best of luck.

Billy.

[tony.673]

Thanks guys. I tried removing the lens and, as Billy says, on putting it back the collimation is still out. I'll give it a try over the next couple of nights on a star and see what happens.

Tony

[John]

I've collimated a bird-jones newtonian. I needed to use an artificial star but a real star (eg: polaris) would have done the job just as well. Laser collimators don't work with that design as has been said. Once collimated the scope performed better and it did manage to split the "double double" star Epsilon Lyrae. Before collimation the star pairs were just two blobs of light even at high powers.