Need a Newtonian 1.25" focuser with diagonal bolt hole pattern

[chuenmanc]

Hello

I recently bought an 8" Portaball on ebay, my first dob. Hooray! Sky was clear-ish on the same night. Hooray! Most of my eyepieces need more in-travel to come to focus. BOO!!!

The scope comes with a basic looking helical focuser, which I thought I could replace with one of a lower profile. However, the bolt pattern is arranged at 45degress diagonally in relation to the axis of the telescope, rather than parallel to it. I can't see any after-market focusers that have this bolt hole pattern. Also, it's only 1.25", whereas most after-market focusers are 2". So two problems really.

Does anyone have any ideas of how to get my eyepieces to focus? Perhaps you've seen a focuser with bolt hoes in a diamond arraangement? Will I be forced to drill new holes, and potentially also make the opening large enough to accommodate the large focuser? Will this cause problems with the secondary mirror not being large enough?

I thought about collimating the mirror upwards towards the secondary, but I doubt there'll be enough travel to do this.

:?

[The Warthog]

For now, putting a Barlow in the focuser will allow you to focus, I'm pretty sure. How much do you reckon you need to tweak the mirror? If it's a very small amount, you may have enough play in the collimation screws to do the trick.

If putting a 2x Barlow in the focuser works, try screwing the Barlow element into your eyepiece tube, for about a 1.5x, and see if that works.

I would be chary of moving the mirror significantly without finding someone to talk to first. It may be something glaringly simple.

[Kaptain Klevtsov]

I'd be tempted to suggest that there are two ways to assemble this thing, one slightly longer than the other, but not having seen one in the flesh I'm not sure.

Kaptain Klevtsov

[chuenmanc]

Thanks for the responses guys.

I recollimated (with a laser) so it was up as high as it could go, so I'll give that a try next clear night. I think I need 3 or 4 mm, and I *might* have got that much from the collimation. Using a Barlow is a good idea - will try that too. I'm pretty sure it can't be assembled to any other length, but I've just been approved for the Portaball yahoo group, so I'll see if there's any more information there.