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The problem with the extension is that unless you pull it all the way out it will more than likely be cocked. Unfortunately that leaves a sizable gap in the focus range -- there is a 20mm range in which focus can only be achieved with the extension at a point other than the ends of its travel. My favored eyepieces achieve focus in this range and thus are almost guaranteed to have axial alignment issues...

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The problem with the extension is that unless you pull it all the way out it will more than likely be cocked. Unfortunately that leaves a sizable gap in the focus range -- there is a 20mm range in which focus can only be achieved with the extension at a point other than the ends of its travel. My favored eyepieces achieve focus in this range and thus are almost guaranteed to have axial alignment issues...

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Hmmm... After re-reading your post a few times, I think I understand what you mean. The drawtube would be slightly tilted (i.e. cocked) and the eyepiece would no longer be axially aligned the focuser and therefore not be fully illuminated by the secondary mirror--is that correct? That is not ideal, but how bad would the effect be? Would they be able to reach focus and if so, would you see vignetting or just some light cutoff or would there be some other issue?

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My children are now the primary users of this scope though I do use it for quick viewing sessions.

I don't know the exact ramifications but I do take steps to minimize any such issues and I've not noticed any in the views. (It just bothers me that the design has this weakness.) I typically pull the extension all the way out which squares it up and then I carefully push it back in just a little bit and try to keep it a squared up as possible while doing so. Once the extension is set like this I don't need to change it through the observing session. Since all but one of my primary eyepieces are parfocal (T6 Naglers and a 16T5 which are all parfocal plus the one outlier being a 31T5), I typically just make sure I collimate after I've extended the drawtube and focused using one of the T6s. Thus the scope is collimated at the point where nearly all the EPs achieve focus and the drawtube doesn't move much through the night.

My children use different EPs and to be honest I haven't been as worried about things being perfect for them. I still try my best to keep the extension squared up but they don't have parfocal oculars. On the other hand, they are happy just to have an excuse to stay up late...

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Just checked -- I have the 08881.

Since the two diagonal holes can be forced to line up so they sort of work, it seems like the holes in general must be very close. Perhaps things are just off by a millimeter or so. If you can confirm this by measuring the distances between the holes or perhaps by inspection when you try to line things up, you might find that a small amount of filing in the correct place on all four tube holes will allow the focuser to be installed with all four bolts.

This might be why they changed the focuser. Perhaps the specs and tolerances were such that a percentage of the scopes ran into this issue.

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The problem with the extension is that unless you pull it all the way out it will more than likely be cocked. Unfortunately that leaves a sizable gap in the focus range -- there is a 20mm range in which focus can only be achieved with the extension at a point other than the ends of its travel. My favored eyepieces achieve focus in this range and thus are almost guaranteed to have axial alignment issues...

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Hmmm... After re-reading your post a few times, I think I understand what you mean. The drawtube would be slightly tilted (i.e. cocked) and the eyepiece would no longer be axially aligned the focuser and therefore not be fully illuminated by the secondary mirror--is that correct? That is not ideal, but how bad would the effect be? Would they be able to reach focus and if so, would you see vignetting or just some light cutoff or would there be some other issue?

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I reinstalled the focuser this time using the top two screws, don't know why I didn't try that last time. When I did this, the bottom screw holes were about ~4mm too far away from where they would need to be. Filing might be the best solution.

To answer my own question about the negative effects: I put in the Cheshire with the extension tube extended and put a decent amount of force in the downward direction, simulating what a Pan 35 would do or equally heavy equipment. It was easy to see that the effect is that the system is no longer collimated--maybe this should have been obvious to me but I didn't realize it until I saw it. When we collimate our scopes, we do it with the cheshire/collimation tool/laser collimator perfectly centered on the light path (ideally). But when a heavy eyepiece or other equipment is able to change the observed light path from the true light path, then you are mis-collimated. I hope I was able to explain it though I don't know the proper terminology.

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I would slot all 4 holes so each hole would only require a little mod instead of a lot of slotting on two holes.

I would use a dremel to oblong/slot the holes.

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Elongate all 4 but be careful not to get leave any filings on inside. I would do it with a round file and some patience.

Of course Mcmaster-Carr has special screws for mis-drilled holes, they are not cheap but they do work...

Jon

Edited by Jon Isaacs (11/19/12 01:57 PM)

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If it were me I'd return that focuser for a GSO 2-speed if you're on a budget; IMO a much better focuser than the Orion. And if you order from Scopestuff, they'll even fit it to a standard Orion flange. If you're not on a budget, then get a Moonlite. Either way I'd send the Orion back.

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