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Orion Low Profile Focuser installation Issue XT8i

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#26 photiost

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Posted 05 October 2012 - 07:27 AM

OK - The older low profile focuser may not simply drop-in to your scope.

I recently upgraded the 10in Intelliscope with a "drop in" Orion focuser with no issues.

In your case I would simply square the focuser and drill/file new holes if necessary.

cheers

#27 Starman81

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Posted 07 October 2012 - 03:07 PM

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...


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?


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.

#28 ThreeD

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Posted 07 October 2012 - 11:21 PM

The tube becoming misaligned after collimation will surely cause an issue. I'm not sure of the effects on the view if everything is collimated with the focuser axis being different than the optical axis *if* collimation is performed with the focuser positioned where the EP achieves focus and the focus is not adjusted afterward.

#29 Starman81

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Posted 18 November 2012 - 03:42 PM

I have been using this low-profile focuser for the past 6 weeks or so and have found it to be a very nice piece of equipment indeed. I do not mind extending the extension tube when needed for different eyepieces and I find the smooth focusing on both the coarse and fine focus to be worth the price of admission.

Now here's where I need some advice before I go irreversibly scarring my OTA... The bottom two holes are off like I mentioned previously, but not by too much. It seems like I could get by with just filing the holes instead of drilling two new holes. Please see the simple schematic drawn below. The holes are not quite that close to being lined up in reality as portrayed by the schematic but you get the picture. If they were I would just try to force the issue but I tried that and it is not possible.

The question is what kind of file and how to go about doing it? Remember, ALL THUMBS HERE!!! Thanks.

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#30 Gastrol

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Posted 18 November 2012 - 04:01 PM

Perhaps a fine, round, needle file?

#31 tag1260

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Posted 18 November 2012 - 04:31 PM

Harbor Freight sells some cheap Jewelers file. In the set is a couple of little round files that will do the trick. If you aren't removing your primary, make sure you tilt the scope down as to not get the filings on it. But then again, you probably already knew that!!!.

#32 Pinbout

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Posted 18 November 2012 - 05:14 PM

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.

#33 tezster

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Posted 19 November 2012 - 10:14 AM

You could also use a drill to 'file' the opening larger.

#34 csrlice12

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Posted 19 November 2012 - 10:43 AM

I'd just send it back and get a two speed focuser that fits. Just even looking at the picture, could you imagine putting an old style ES82 30mm on that extended sight tube??????????

#35 Starman81

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Posted 19 November 2012 - 11:06 AM

Thanks guys, these are all good suggestions. The old adage 'measure twice, cut once' in this instance means that I better get a little practice before operating on my OTA.

#36 rick-SeMI

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Posted 19 November 2012 - 12:36 PM

Would smaller screws fit ?

That would save on shavings...

BTW, your clear sky chart looks just like mine :) :bawling:

#37 Jon Isaacs

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Posted 19 November 2012 - 01:56 PM

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.


:waytogo:

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

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#38 Starman81

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Posted 26 November 2012 - 01:36 AM

The two screw only setup was definitely straining the OTA. See the indentations above the upper screw holes.

As suggested, I elongated all 4 using a round file with good results. Now the focuser fits great, just have to recollimate and I should be set. Thanks guys!

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#39 Starman81

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Posted 26 November 2012 - 01:38 AM

I expected as much, what with this kind of load:

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#40 BDS316

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Posted 26 November 2012 - 12:39 PM

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.



I put a Moonlite on my XT8. Works great with a 1.75 inch travel drawtube and the 1 inch spacer. All eyepieces come to focus including 35 Pan and 31 Nagler, and the tube stays out of the lightpath.

Some would say the Moonlite is overkill on the XT8 but mine originally had the Rack and Pinion, and I could always switch the Moonlite to a future scope down the road.

http://www.astrogood...e.goldeneye.jpg

#41 Starman81

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Posted 26 November 2012 - 01:11 PM

That is a sweet-looking scope Bryan! I was definitely considering the Moonlite as well, but found a good used deal on the focuser mentioned in this thread and was luckily able to make it work.

Do you have to use counterweights for the Moonlite? I don't see any in the pic but I know others have stated such.

#42 BDS316

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Posted 26 November 2012 - 01:33 PM

That is a sweet-looking scope Bryan! I was definitely considering the Moonlite as well, but found a good used deal on the focuser mentioned in this thread and was luckily able to make it work.

Do you have to use counterweights for the Moonlite? I don't see any in the pic but I know others have stated such.


I have used a few different counterweight systems on GoldenEye (so named for the Golden colored Moonlite) but the focuser isn't that heavy. Balancing is for the Telrad/dew shield and the heavy eyepieces more than anything.

I got epoxy-coated doughnut magnets 3 inches diameter about half a pound each form American Science and Surplus for a few bucks each and three of them balance the scope nicely when put on the bottom of the tube opposite the focuser and Telrad, not seen in the picture.

#43 Starman1

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Posted 26 November 2012 - 03:33 PM

The OP's replacement focuser is made by LongPerng in Taiwan, and is every bit as good as the GSO focusers.
The issue is the sliding focuser tube, and here is how to use it correctly.
Find out which eyepiece requires more out-movement of the focuser to achieve focus. Slide the tube out *just* to the point where this eyepiece focuses. Lock the drawtube slider in place at that point and never move it again. You can measure how far out it is at several points if you think it's not square.
Since every other eyepiece should come to focus with the focuser slightly racked in, this should allow all eyepieces to focus with the least amount of extension on the sliding tube.
By the way, the sliding tube was designed around the use of cameras, which typically require a much more Inward position of the focuser than eyepieces.
I've used this focuser and like it a lot.






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