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Posts Made By: Rod Nabholz

October 11, 2003 02:54 PM Forum: Equipment Talk

Refractor Focuser Alignment

Posted By Rod Nabholz

I recently acquired a collimation laser and I thought I would check the alignment of my refractor's focuser, which I had my suspicions about.

I cut a disk out of a manilla folder matching the inside diameter of the dew shield and inserted it in the shield up against the front of the lens cell. The center marked for reference.

It seems that indeed the focuser is not square. The laser's dot misses the center mark by about 3mm. (4" f10 by the way)

My question: Is this enough error to worry about? The focuser is not adjustable so I will have to undertake some work to bring it true, and am wondering if I will see a noticable improvement in performance for the trouble.


By the way, I also got multiple return dots on the laser (EZCollimator) so I am also wondering about the cell's alignment too.

October 19, 2003 05:25 PM Forum: Telescope Making

A Scope for the Kids

Posted By Rod Nabholz

I finished a small project for the kids and have put together a little site with some pics and thoughts on the project. If you are interested you can see it at:

Here is a shot of the Kid Peek Telescope

March 2, 2004 08:54 AM Forum: Equipment Talk

Tal Gem-3RA mount - Experiences?

Posted By Rod Nabholz

I am looking for a solid mount for strictly visual observing and came across this unit.

I like the high capacity (40 lbs) although I will not come close to using it immediately, it is nice to have that capacity available in case of future acquistions ;^).

Anybody out there used one of these? What are your impressions

May 2, 2004 02:52 PM Forum: Telescope Making

Help with Mirror Cell

Posted By Rod Nabholz

I am embarking on a rebuild of a 13.1" Coulter Blue Tube to a truss tube style. This is my first project of this scale and I have a question or two about the mirror cell.

The Mirror is 13.1" and 1.125 thick. I have decided to go with a 9 point cell, mostly because that mimics the support pattern of the original tailgate design. Do you think that 9 points is the correct configuration for this mirror?

I am patterning my cell loosely after the Kriege design and have come to understand it's basics from reviewing web sites outlining various projects. One thing that I can't seem to visualize is how one attaches the support triangles to the collimation screws in a manner that keeps them free floating. Can amyone provide any insight?

Is mirror attachment best accomplished with silicone? I have used silicone on a small downward looking Binocular scanner and it seems to work well, but the mirror is much smaller and lighter (and less expensive) so I ask your guidance.

Lastly, I am probably missing an obvious easy answer, but in visualizing the process of attaching the mirror to the cell, How do you manage to make sure the mirror is centered. I wouldn't want to make a mistake in this step.

Thank you for reading this and any insights you can offer.


June 14, 2004 10:51 AM Forum: Telescope Making

Source for 2" OD .065 Thickness Aluminum Tube?

Posted By Rod Nabholz

Can anyone recommend an inexpensive source for aluminum tubing that is 2" OD and .065 wall thickness?

Mail order sources are great, but a local source in NE Iowa would be even better.

Thanks for any ideas


July 6, 2004 07:50 AM Forum: Telescope Making

Question Regarding Mounting Altitude Bearings

Posted By Rod Nabholz

I am at the point in my project where I need to mount the altitude bearings on the mirror box. I have determined the balance point of the assembled box, trusses and secondary assembly.

I am using half circles for the altitude bearings.

My question is how do I center the bearings on the balance point? My Understanding is that I would use the intersection of the midpoint of the diameter (middle point of the long side of the half circle) and the midpoint of the radius (half the height of the half circle) centered on the mirror box balance point?

Wow, that was hard to describe, I hope you get my drift and can help a confused first timer. Thanks

July 25, 2004 03:45 PM Forum: Telescope Making

It's Done, Thanks for the help

Posted By Rod Nabholz

I have finished my twin truss 13.1 f4.5. Before and during the process of planning and building I posted a few questions that were always answered quickly with great advice and expertise.

This was my first project of this size, and It was extremely gratifying last night at First Light.

I hope to flesh out the following pages with some narration about my reflections on the process, but for now here are some pictures.

Thanks again all!

August 1, 2004 08:12 AM Forum: Telescope Making

Hexagonal Star Test - Ideas??

Posted By Rod Nabholz

I had a chance to get out with my newly reconfigured 13.1" scope last night ( )and did some testing.

The star test is showing a clear hexagonal shape at high power and I could use your ideas as to how to diagnose the problem.

Some stats first.

13.1" f4.5 mirror
1 1/8th" thick
9 point cell as spec'd by Plop
3.1" secondary attached by silicone

Arguments in Favor of improper support by Cell

1. Thin Mirror, maybe 18 point would be a better choice?

2. Hexagonal Pattern suggests pattern that would result from 3 outer pad sets and 3 spaces between.

Arguments against improper support by cell

1. Previous Coulter Tail Gate cell was a 9 point with no observed problem.

Arguments in Favor of Secondary as cause

1. Silicone mounting could have stressed secondary

2. Previous Coulter mounting was 2.5" square double sided tape, Better support?

3. One of the 3 silicone pads shows concave sides instead of convex, Maybe the culprit?

Arguments against Secondary being the cause

1 Trouble visualizing how a secondary mounting with 3 pads would cause the hex pattern.

Well you have my thoughts, What do you think?



August 26, 2004 09:41 AM Forum: Telescope Making

Construction Notes on Coulter 13.1" rebuild

Posted By Rod Nabholz

I have posted some notes on the construction of my newly completed telescope.

I thought some of you might find it interesting.

You can find it here:



January 26, 2005 08:17 AM Forum: Telescope Making

A little electronics help

Posted By Rod Nabholz

I am trying to end some fumbling with flashlights at the telescope by rigging some led lights to illuminate my setting circles.

I have made some simple lights from a 2 AA battery holder and an LED. I want to attach these to the mount, and then by pushing a button have them illuminate for a timed period, say 15 to 20 seconds and then go out.

I could use some help finding the appropriate switch. Can some one guide me to a suitable switch component to make this work? My knowledge of electronics is basic at best, so any other information I should have to make this work would be appreciated as well.