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Equipment Discussions >> Equipment

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Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: ThreeD]
      #5453405 - 10/03/12 11:21 AM

Quote:

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?


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ThreeD
Pooh-Bah


Reged: 12/23/08

Loc: Sacramento suburbs
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5453413 - 10/03/12 11:24 AM

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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ThreeD
Pooh-Bah


Reged: 12/23/08

Loc: Sacramento suburbs
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5453451 - 10/03/12 11:50 AM

Quote:

Quote:

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?


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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Phil Sherman
Pooh-Bah


Reged: 12/07/10

Loc: Cleveland, Ohio
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: ThreeD]
      #5455048 - 10/04/12 12:50 PM

I needed to pull the extension tube partway out to reach focus when using my DSI camera. The cocking problem was quite an issue until I discovered a solution to it.

I cut a piece of 2" schedule 40 water pipe that was the correct height to make a collar for the slide out portion of the focuser. A hacksaw cut it in half lengthwise and, after heating it, I was able to form it to the exact size of the slide out section of the focuser by pressing it against the focuser. I use a rubber band to hold the two sections of plastic pipe to the focuser and it makes a solid platform for the camera.

Phil


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Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: ThreeD]
      #5455349 - 10/04/12 04:31 PM

Quote:

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.




Thanks ThreeD for the good idea, as soon as I get a chance I will look at how close the screws are to the holes and see if they could be filed down.


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photiost
professor emeritus
*****

Reged: 12/14/06

Loc: Montreal, Canada
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5456208 - 10/05/12 08:27 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


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Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5459507 - 10/07/12 04:07 PM

Quote:

Quote:

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.


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ThreeD
Pooh-Bah


Reged: 12/23/08

Loc: Sacramento suburbs
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5459956 - 10/08/12 12:21 AM

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.

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Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: ThreeD]
      #5526360 - 11/18/12 03:42 PM Attachment (13 downloads)

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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Gastrol
Pooh-Bah


Reged: 11/04/11

Loc: los angeles
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5526388 - 11/18/12 04:01 PM

Perhaps a fine, round, needle file?

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tag1260
scholastic sledgehammer
*****

Reged: 10/07/12

Loc: Ohio, USA
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5526430 - 11/18/12 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!!!.

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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5526497 - 11/18/12 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.


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tezster
scholastic sledgehammer
*****

Reged: 07/14/09

Loc: Missisauga, Canada
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Pinbout]
      #5527614 - 11/19/12 10:14 AM

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

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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: tezster]
      #5527670 - 11/19/12 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??????????

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Starman81
Carpal Tunnel
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Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: tezster]
      #5527704 - 11/19/12 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.

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rick-SeMI
sage


Reged: 01/08/11

Loc: Michigan - USA
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: Starman81]
      #5527863 - 11/19/12 12:36 PM

Would smaller screws fit ?

That would save on shavings...

BTW, your clear sky chart looks just like mine

Edited by rick-SeMI (11/19/12 12:39 PM)


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Orion Low Profile Focuser installation Issue XT8i [Re: Pinbout]
      #5528032 - 11/19/12 01:56 PM Attachment (6 downloads)

Quote:

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.






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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Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Orion Low Profile Focuser installation Issue XT8i [Re: Jon Isaacs]
      #5539722 - 11/26/12 01:36 AM Attachment (9 downloads)

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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Starman81
Carpal Tunnel
*****

Reged: 03/06/08

Loc: Metro Detroit, MI, USA
Re: Orion Low Profile Focuser installation Issue XT8i [Re: Starman81]
      #5539723 - 11/26/12 01:38 AM Attachment (7 downloads)

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

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BDS316
Carpal Tunnel


Reged: 09/16/09

Loc: Sol 3
Re: Orion Low Profile Focuser installation Issue XT8i new [Re: simpleisbetter]
      #5540249 - 11/26/12 12:39 PM

Quote:

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.astrogoods.com/stone.goldeneye.jpg


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