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Equipment Discussions >> Classic Telescopes

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shawnhar
Postmaster
*****

Reged: 06/25/10

Loc: Knoxville, TN
Re: Just received an Odyssey Compact. Need some help.. new [Re: Dan F.]
      #4631689 - 06/10/11 08:29 AM

Nice cleaning job! That mirror came out much cleaner than mine ever will!
I was very surprised to see a 9 point floating cell and collimation rods up the tube, certainly not stock. I think you will have much fun with this scope and with your skills you will have no problem getting where you want to go.
Those little "squares" are the retaining clips, they are only there to keep the mirror from falling out and should never be tight. If you do tighten them you will see stars that look all funny shaped, shockingly little pressure can deform the mirror's shape and affect the view.

Oh yeah and collimation, cheapest effective tool is a Newtonian collimation tool, or combination tool, it has a sight tube, crosshairs and cheshire all in one, this allows you to place and tilt the secondary and tilt the primary with one tool. I have the Orion one, all metal, very good.

Edited by shawnhar (06/10/11 08:37 AM)


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apfever
Carpal Tunnel
*****

Reged: 05/13/08

Loc: Colorado
Re: Just received an Odyssey Compact. Need some help.. new [Re: Dan F.]
      #4631836 - 06/10/11 09:59 AM

I believe the original cell had the primary just siliconed to it. My coulters were all glued mirrors, even the 17.5 inch. Somebody has cut the cell, added the 6 retainer post, added the 9 point triangles, and added the collimation rods that go to the top. There must be some sort of holder to keep those rods from flopping around in the tube.

You need to examine the cell to see how it has been modified and check for the rods tilting the cell correctly.
In other words, make sure the collimation action is legit.


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Dan F.
member


Reged: 07/05/10

Loc: Kalamazoo, MI
Re: Just received an Odyssey Compact. Need some help.. new [Re: apfever]
      #4631937 - 06/10/11 11:11 AM Attachment (27 downloads)

Yeah, that's the problem...there's actually some play in the action. But I'm wanting to build a new cell anyway, so it's not a big deal.

So the clips shouldn't be tight, but can they be touching the mirror so as to keep it from flopping around like it had been? I'm thinking I'll have the collimation action between the new base and the structure that holds the flotation points, and the clips will come off that structure so the mirror won't move relative to the clips when being collimated. Thoughts?


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: Just received an Odyssey Compact. Need some help.. new [Re: Dan F.]
      #4632125 - 06/10/11 01:08 PM

You need to support the edge at the C.G. of the disk edge in at least two points.

The sole advantage of the Coulter cell - besides being cheap - is to have no clips obstructing.

One can have tabs extending from the T frame with a bearing point approx 0.7" up the edge of the mirror, then secure the mirror with the tape (or other means). The tape doesn't bother me - it functions like the clips if done in moderation.

The original "red tube" cell is three pieces of particle/OSB board - the outer cap that is visible, adhered to another that form-fits the inside of the tube, and a third that supports the mirror, which is attached to the two other boards via 6 screws in a push/pull configuration. Mirror rides on three foam pads (in mine incorrectly located), with the edge attached with a single continuous strip of duct tape running twice around the circumference, and finally secured by a "pipe clamp" that joins the mirror/board edge in a balanced manner.

The Orion DSE cell was three enormous blobs of silicone glue (approx 2" diameter and 1/2" thick) with duct tape surrounding - no pipe clamp. Three one inch holes for ventallation, otherwise very similar (not a push/pull but very stiff springs and wing nuts.


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Dan F.
member


Reged: 07/05/10

Loc: Kalamazoo, MI
Re: Just received an Odyssey Compact. Need some help.. new [Re: wfj]
      #4632635 - 06/10/11 06:24 PM

So what you're saying is that a mirror riding on the six or nine points but also duct taped around the lower piece (same dia. as mirror) can be just as effective as clips? In the above example would that simply mean having a half inch wood ring between the "T" and flotation rocker mounting points?

I stopped in the hardware store today to see what kind of square tubing they had. Turns out I could get four feet of some aluminum or steel stuff of roughly one to one and a half inch for ten bucks. Is there anything specific I need to pay attention to here, or will this be sufficient? Which material should I choose?

I've seen some cells that mount in a tube with just three metal angles as attachment points rather than utilizing a full wooden ring. Should I lean towards one method over the other?

I'm seriously debating redoing the spider / secondary mount as well, both for collimation purposes and so I can learn what's involved. I did some research like I did for the mirror cell but found next to nothing. Can anyone point me in the right direction, e.g. forum threads, websites, etc. Thanks!


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: Just received an Odyssey Compact. Need some help.. new [Re: Dan F.]
      #4632698 - 06/10/11 07:12 PM

Check out:
http://www.cruxis.com/scope/mirroredgecalculator.htm

What I meant was two (or three) brackets with a bearing point along the side, positioned at a point midway up. If the mirror was flat, it would be at half the thickness of the mirror.

The point of the tape around the periphery of the mirror would be to restrict the movement of the mirror - just like mirror clips. And like them, the idea is to not have any force incident on the mirror in the normal operation of the scope, thus they don't distort the mirror. The normal load path is through the bearing surfaces ONLY. The clip/tape is to secure so that if inverted, the mirror doesn't fall out.

Do not recommend a tight ring around the mirror of firm material as thermal expansion might bind and buckle. Another approach is to use a edge support strap.

Do more research on cell design. You need to understand more.

I'm thinking of a low profile design (my mirror is further back in the tube, requires it) out of 3/8" square extruded aluminum in two T sections joined with collimation screws. Three bars with pivots in center and nylon pads at ends. Two outrigger brackets support the edge through a nylon bearing as a single point of contact. Tape surrounding mirror as in the original cell - that doesn't bother me.

Other links:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2672155/page/0/view/collapsed/sb/5/o/all/fpart/all/vc/1
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2804256/Main/2800258


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Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
Re: Just received an Odyssey Compact. Need some help.. new [Re: wfj]
      #4633375 - 06/11/11 08:22 AM Attachment (28 downloads)

Here's a 6-point cell that I made for a 12.5-inch scope. It shows the edge supports and clips well. In this case there are 4 supports because the scope is on a equatorial mount. The edge supports are at 90 degree intervals and have nylon bolts positioned at the mirror edge center of gravity (about half way up the edge).

JimC


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Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
Re: Just received an Odyssey Compact. Need some help.. new [Re: Mirzam]
      #4633377 - 06/11/11 08:24 AM

I must say though that the original cell that came with your telescope looks like it was thoughtfully constructed.

JimC


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George S
newbie


Reged: 11/18/09

Re: Just received an Odyssey Compact. Need some help.. new [Re: Mirzam]
      #4633939 - 06/11/11 01:08 PM

You probably have this already,JMI has a document section on their website. I hope this helps.

http://jmitelescopes.com/pdf_docs/max_manual.pdf


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wfj
Pooh-Bah
*****

Reged: 01/10/08

Loc: California, Santa Cruz County
Re: Just received an Odyssey Compact. Need some help.. new [Re: Mirzam]
      #4634154 - 06/11/11 03:20 PM

Quote:

I must say though that the original cell that came with your telescope looks like it was thoughtfully constructed.

JimC




My criticism of it would be just the "slop" and "flop" aspects in its concept of "edge support". One could also improve the ventilation as well.


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Dan F.
member


Reged: 07/05/10

Loc: Kalamazoo, MI
Re: Just received an Odyssey Compact. Need some help.. new [Re: wfj]
      #4634267 - 06/11/11 04:37 PM

@Jim, I wonder if I can / should just fix the current cell and use that for now instead of constructing a new one (which I am also fine with).

@George, thanks. I actually found this the other day and proceeded to confirm that the system is working properly.

@wfj, from what I'm hearing it seems I'm going to need some guidance / directions in either dealing with this current cell or constructing a new one. Some things I understand, others I have yet to understand


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Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
Re: Just received an Odyssey Compact. Need some help.. new [Re: Dan F.]
      #4635130 - 06/12/11 08:13 AM Attachment (28 downloads)

Hello Dan,

A 6-point cell can be built with one trip to the hardware store. Here's picture of one that I use for my 14-inch. The mounting plate is honeycomb aluminum panel but could just as easily be wood. A little flexure in the mounting plate does not matter. Note the use of box channel (and a lot of little nuts and bolts) to build the support frame.

JimC


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Dan F.
member


Reged: 07/05/10

Loc: Kalamazoo, MI
Re: Just received an Odyssey Compact. Need some help.. new [Re: Mirzam]
      #4635244 - 06/12/11 10:04 AM

Jim, thanks for the photos. I like the previous design that you posted before this one. But I have a question. When I see cells such as yours, I see no silicone...I thought using silicone was the best way to mount the mirror. Is either method fine?

On another note, I just noticed on my coulter cell that the cardboard triangles used for the nine point were flexing to the point that the mirror essentially rests on the mounting posts rather than the points. Would aluminum strips eventually do the same thing with the eight pound mirror, and if so, would it be better to use square tubing like you do in your designs?


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Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
Re: Just received an Odyssey Compact. Need some help.. new [Re: Dan F.]
      #4635452 - 06/12/11 12:01 PM

I didn't notice that your triangles were cardboard! Definitely not a good thing to be resting on the mounting posts. Aluminum sheet, thin steel or wood will work well. I like the simplicity of the box channel design but a mirror as light as yours will not tax things too much.

Incidentally, properly designed 6-point cells are usually superior to nine point cells for small mirrors. This is based on finite element analysis. See for example:

http://www.atmsite.org/contrib/Holm/Plop_optimized_cells/index.html

For my travel scopes like the 14-inch, I take the mirrors out and so do not use silicon. The 12.5-inch scope uses mirror clips that do not quite touch the mirror surface but will keep it from falling out if tilted down. This scope is permanently mounted.

JimC


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Pulsar345
newbie


Reged: 01/21/13

Re: Just received an Odyssey Compact. Need some help.. [Re: bob midiri]
      #5635361 - 01/21/13 05:07 PM

I know this is an old thread but could you post some pix of these mods, and maybe the best place to source teflon pads. Thanks

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Glen A W
professor emeritus


Reged: 07/04/08

Loc: USA
Re: Just received an Odyssey Compact. Need some help.. new [Re: Dan F.]
      #5636588 - 01/22/13 10:26 AM

A great thread anyhow. It always amazes me how scopes fit the times. A scope like the Odyssey just takes me back to 70s-80s observing. Let us know how much fun you have been having with it. GW

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