The Finishing Touches
Focuser
The Coulter had a nice 1.25" rack and pinion focuser, but I did want to upgrade to a 2" so I went shopping for focusers. I must admit, there are some amazing products out there for those seeking a very high level of fit and finish. Unfortunately, most of the time they carry a price tag that matches. I considered some of those products, but in the end simply could not justify the cost, it could have doubled the entire budget of the project! I found a great product on Astromart in a used JMI Reverse Crayford focuser. It was a bargain at $75 with the 1.25" adapter. I am quite pleased with it, and do not feel that the performance of the scope has been compromised. I am sure that those other products are great, and if the budget wasn't a consideration, I might like to have one, but this one is performing just fine.
Finder
The Finder in this scope is an early example of the Rigel QuickFinder. I have owned this product for years, and this is about the 4th scope it has been mounted on. It is a solid performer and perfect for situations in which a Telrad is too large or heavy. You can see here that I have rigged up a home made dew shield for it. Unlike the current product, the early units did not have one.
Manual Altitude / Azimuth Pointing System
I own and use a Windows Pocket PC based PDA, a Hewlett Packard Jornada 548. I purchased and use TheSky Pocket Edition to have a very capable planetarium program at my disposal wherever I am. In surfing the web, I came across the concept of using this type of set up to provide real time altitude and azimuth settings to aid in pointing telescopes to a desired target. Since I already had the PC and Software, it seemed a natural for me to implement a system like that on my scope.
My first implementation was on the Coulter. I made an azimuth dial to ride between the rocker and ground board, and came up with a protractor like scale for the altitude bearings. This arrangement required accurate leveling in order to make the altitude readings accurate. When properly set up I found myself able to place objects in, or very nearly in the field of a low power eyepiece. This made finding objects relatively quick and easy and was a feature I was definitely going to include on the new design.
To improve things, I made a couple of changes. On the Coulter, the retrofit meant that the azimuth dial made from masonite extended beyond the footprint of the rocker and ground board. It was susceptible to breakage during transport or by a misplaced foot out under dark skies. The new dial would be entirely covered by the rocker, and would be visible through an aperture cut into the side and base of the rocker.
The other improvement dealt with the Altitude scale. As I mentioned, having the scale mounted to the altitude bearings meant that the scope had to be quite level to avoid introducing error into the system. In trying to eliminate that potential for error, I decided to use an inclinometer for the altitude scale. By using the inclinometer, the altitude position of the "tube" is read independently of the position of the rocker and the ground board, making leveling the scope less critical.
In use, when setting up the scope I am careful to orient the rocker and ground board so it is facing to the North as indicated by a small compass laid parallel to the side of the rocker. (Magnetic deviation just happens to be very low here in Iowa, so this gets me close. You may have to compensate appropriately for your area). The inclinometer is attached to the scope via it's magnetic base to a small steel plate attached to one of the upper tube channels. In the photo you can see a safety lanyard that prevents any potentially disastrous falls onto the mirror. Then, using a known object centered in the field of view, I consult the computer and make any corrections to the azimuth dial as indicated,( In the photo I had not yet installed the pointer ) and confirm that the inclinometer matches as well. I am now set up and ready to observe.
I do find that the system works best if when making big sweeps to a new area of the sky, I take a moment and realign with a known object in that region of the sky. It is not absolutely necessary, but I find it is time well spent. I tend to concentrate on small areas of the sky searching for deep sky objects so this suits me fine. If you tend to bounce all over, this might be less convenient.
To read more about how this system has evolved
since the writing of this article, Click Here
So How Does it Work?
I am very pleased with, and proud of the scope.
It is much more manageable to move, at just 65 lbs. (mirror box and focuser board 45 lbs, and Rocker 20lbs) it is just slightly more than half the 125 pounds that the Coulter weighed. The package all bundled up is approximately 18"x18"x25" plus the tubes. There is always room to take it along.
It sets up in 5 to 10 minutes total, with one tool used in just 4 places, a 9/16ths wrench that I use to tighten the tubes down into their channels. I keep the wrench in my eyepiece case to make sure it is always with me.
It holds collimation quite well throughout it's range of motion. Collimated at 45 degrees, there is some movement as I observe the laser's dot and move the scope through it's entire range of motion. The motion is very small, less than half the diameter of the center of the collimation ring on the primary. The Autocollimator confirms that the scope retains highly accurate collimation throughout all but the last 10 degrees at each end of it's range. Because of the extreme accuracy of the autocollimator and the small total movement of the laser, the effects are well within acceptable limits as far as I am concerned. There is no noticeable effect at the eyepiece.
It cools quickly. As I mentioned in the opening, the old scope never cooled. I truly feel that I am just now for the first time seeing the capabilities of the optics unimpeded by the structure. I am considering adding a cooling fan to the mirror cell to facilitate even quicker cooling.
It dampens from a hard rap in 2-3 seconds, and movement is non existent to sub one second to settle on normal touches.
Balance and movement are very good. I don't think I could add much to the top end without some counterweight, but for now I don't feel the need to add anything to the current set up.
What Did I Learn?
1. Patience. Perhaps because I was doing something completely new, and was a little nervous about the outcome, I took my time and really thought about and planned the project. As a result, I feel that I avoided many potential surprises that could have slowed, maybe even killed the project.
2. New Skills. As I mentioned, I was really not very experienced in using routers. I got much more comfortable with them during the course of this project. I also had my first attempt at turning wood on the lathe. That was a lot of fun, but make no mistake, I have a new and deep appreciation for those who have mastered that skill.
3. Not to underestimate the cost of the "small stuff". When budgeting for the project, I really had no idea how much the small stuff like bolts, nuts, washers, etc would cost. Not only did it add up to more than I expected, I seemed that I was visiting the hardware store daily at one point to pick up just one more of this and a couple of that....
4. Admiration and appreciation for those who have gone before. By this I mean those who have conceptualized, experimented, built, rebuilt and tested all of the various designs and concepts that I borrowed and compiled to make my own scope. Their work made mine much easier.
5.The Joy of The Outcome. I am proud of this telescope. Every time I get to show it to someone new, it is a real kick for me. It is a humble project compared to many I have seen in person and on the net, and I have no illusions of this being an original concept or a design breakthrough. It is just that this one is the one that I built.
Links
Here are a few links that I drew on during the planning and construction of this scope. Thanks to all those who took the time to share their creations, provide a source for materials or otherwise contributed.
Two Tube Scopes
A Scope Like Alice - Ron Ravneberg's great 2 tube travel scope
-- http://www.atmsite.org/contrib/Ravneberg/alice/
12.5" Two Tube - Peter at Kitgear's great 12.5 incher
-- http://www.kitgear.com/my_first_scope.htm
12.5" Two Tube - Dave North's excellent 12.5"
-- http://timocharis.com/twelve/
10" Inch Two Strut - Bob Bunge's two strut scope
-- http://ladyandtramp.com/10-inch/
Manual Altitude/Azimuth Pointing Systems
StarTrak - Application for Psion Handheld for Real Time Alt Az Coordinates with resources for making Alt and Az scales
-- http://www.startrak.co.uk/ConsTips.htm#Marking
TheSky Pocket Edition - The software I run on my Pocket PC
-- http://www.bisque.com/Products/TheSkyPE/TheSkyPE.asp
Suppliers
McMaster Carr - Unbelievable source of all kinds of materials, hardware etc
Meridian Telescopes -- Ebony Star Laminate in Project Size quantity
-- http://www.meridiantelescopes.com/index.htm
JMI -- Excellent focusers and other Astro Products
I hope this has been of some value, or at least entertainment to you. If you have questions or comments, I welcome them at :
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Eyepiece BagVintage Telescope Restoration Towa 339 "Katana"
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© 2005 Rod Nabholz
