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 Frequently Asked Questions
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Which size Teleport is right for me?Ultimately, of course, you will have to answer this yourself, though I can give you a few comments that may be helpful. The photo shows the original three sizes, but not the new 12.5." For portability, the 7" is my first choice and for viewing it’s the 14.5" (duh!). The I0" seemed to be the best compromise until I made the first 12.5" in 2006. It's closer to the 10" in weight and to the 14.5" in performance, and it's now my overall favorite. It seems to fall even nearer than the 10" to the middle of the size range for which the Teleport concept is practical. It's the most advanced design and offers the best overall value.
I regard the 7" as the most specialized. It is ideal for folks with a physical limitation, or with very little storage or transport space available. It was expected to see a lot of use as a carry-on for flights, but changes in airline regulations in recent years often preclude that. It’s a great scope, but it is a bit short for taller folks, and it’s certainly expensive for its aperture. But then so is one of Roland’s APO refractors, and neither of us can do much about that. It just takes a long time to make either, and the 7" takes almost the same time and material as the 10".
The 14.5" is an awesome observing tool. It’s extremely comfortable for me at 6’2", and even for folks several inches shorter. It’s the shortest and easiest to use scope of that aperture that’s commercially available so far as I know. Its quick setup, rapid mirror cooldown system, and the standard Feathertouch focuser add much to its value and pleasure. Still, it moves into a different category than the 10" in terms of handling, transport, and cost. At 68 lb, it’s not a scope you pick up in one hand and stroll across the field or plop it into your car seat and take off. The extra time and effort it requires is right for some observers and not for others. I ’m working on one the size and weight of the 7" that pops up into a 14.5" inch performer, at the cost of a 10". Don’t hold your breath. :-)
For a long time I thought the 7", 10" and 14.5" sizes of the Teleport pretty well covered the range within which its extending strut design is practical. The cost of such a design is prohibitive for smaller sizes, and larger ones would need the greater rigidity of a truss. More recently, I developed the 12.5" to fill the gap between the 10" and the 14.5." It seems the best of both those worlds and quickly became my personal favorite. It advances Teleport technology by applying what I've learned over the past 10 years. I am so pleased with it that I plan to build only that size in '08 and '09.
I’ve been working on ideas for a 20". It won’t have extending struts, so it will be a bit slower to set up. Still, it will be smaller, lighter, and quicker to set up than any other 20" I’ve seen. It will incorporate the other important Teleport features and more, so it will be a full featured scope. I hope to build one for myself in a couple of years, but don't plan to put it into production.
I’m tempted to say, "Because the LTFWT Swiss Army knife gets dull and has to be sharpened really often." In a way, that’s almost the real answer.
Many high end scopes are hand built, but Teleports require many more demanding steps. Everything is lighter and more precise. It's like making a fine guitar compared to a bookcase, and it takes longer. The design also requires many special components that I must also make by hand. Tolerances are closer than in other Dobs, and each extra built-in feature unique to the Teleport requires parts that I must also make.
I’ve made fixtures and added equipment to reduce the time to make Teleports, but it still takes over 100 hours to make a 7" or 10", and about 130 hours for a 12.5" or a 14.5". Just the application of the Polane finish on a batch takes six full days. Linda spends a good long day making each cover, and she isn’t slow. These are straight shop time hours, exclusive of any design work, prototypes, engineering, sales or service.
Thus I can build an average of around a dozen telescopes a year in a batch of one of the three sizes. If I built one scope at a time, the hours per scope would nearly double. Small batches of 5-10 seem to be the best tradeoff overall.
My previous answer clearly prompts this question. It may may seem odd to some, but it’s clear and easy to me. I did that already, and I won’t do it again. In the mid-eighties, fifteen people worked for me building film processors. I spent all my time managing people and none of it making things. I wasn’t happy with doing that, nor with the results. I wasn’t an effective manager, and the business barely survived financially.
I can’t imagine anything more fun to make than telescopes. When I decided to do that, I promised myself I would do it alone. I’m reasonably competent to manage just me, and happy doing it. Linda makes the shrouds, covers, and manuals, and does this web site as an independent contractor. (and I do mean independent ;-)
I'm working on some ways to increase the production of Teleports, within my self-imposed limitations. They will never be a mass-production item, but I am gradually reducing their delivery time.
The short answer is "Rigid enough". Now "the rest of the story."
First, four struts can never be as rigid as eight truss poles. Some scope makers call their four struts a "truss", but it isn't. A triangle is the ultimate structural polygon. It can flex only if the length of at least one side changes, and the material resists that far better than it resists bending. A Serrurier truss, commonly used in larger portable scopes, demands no stiffness from its poles. It only requires they not stretch or compress much, which demands little from the material.
But four struts require stiffness. The secondary cage applies a bending moment (not just compression and tension) to the struts. They can bend easier than they could stretch or compress. Still, the Teleport struts work well because of three main factors:
The second and third factors both reduce the need for rigidity. The three together make the Teleport work well enough that the director of the Instrumentation Laboratory at The Kennedy Space Center said, after he tracked a satellite with one at the Chiefland Star Party "That’s the sweetest moving telescope I’ve ever used." (Yes, he authorized the quote)
The Teleport's extending struts are at the heart of its concept and its unique advantages. They allow it to be far more compact and quicker to set up than other scopes. You can’t see anything with the most rigid scope in the world if you can’t take it to where you can observe or don’t have enough time to set it up.
In the case of the 14.5", I developed sliding rings for each of the struts. After the struts are extended, the rings are slid up to engage a "C" block. That locks the strut to the mirror box top about a third of the way up its length, effectively shortening the strut by several inches. Since the flexure of a strut under a given load is proportional to the cube of its length, shortening them just those few inches greatly improves the rigidity.
The quickest way to check the overall flexure in a telescope is to insert a laser collimator, set the collimation, then move it up and down through its normal range of altitude and turn it in azimuth. The laser spot on the collimator face will move depending on the amount of flexure.
With the Teleport, a movement of a couple of mm is typical with clean bearing surfaces and proper setup. As with any scope, the collimation should be set with it aimed near the middle of its useful altitude range. Since seeing is better for higher objects anyway, I suggest about 60 degrees up.
Collimation error resulting from this small flexure doesn't have a detectible effect on the image quality.
That's an issue with any Newtonian, and especially so with those that get moved around and taken up and down. The Teleport holds it's collimation well considering those factors, provided the opening procedure is properly done. Of course it isn't like a heavy solid tube Newtonian on a fixed mount.
Three main factors greatly reduce collimation issues:
This and the next section apply for three post Teleport cells with slings, serial numbers under TP10-044. For the newer type four post cell, no adjustments in post position or sling tension are needed. Teleport cells are not typical. The must provide nine support points in a smaller space, with lighter weight, than a three-point typically would. The combine some features from equatorially mounted Newtonian cells and typical Dobs, then add a few new twists.
The following isn’t complete, but is a general explanation that will supplement and help clarify the step by step instructions in the manual.
When you remove the locking plate and set up a new scope after shipping, or after cleaning your primary, two things must be set.
The top post must be rotated so it is as far up in the cell as possible. It was rotated down against the mirror edge during shipment, but now it must be moved up to provide the needed mirror clearance. The top post screw is off center and is tight within the post, so turning the screw will turn the post and also move it closer to or farther from the mirror.
The first photo shows the top post as it is during shipment, down and in contact with the mirror edge. In the second photo, the post has been rotated to its highest position. Note how it clears the mirror and is now closer to the top edge of the cell.
A small notch on the top post screw should point up when the post is at the top as shown in the second photo. The notch is there so you know the post orientation when the cell is in the scope and you can’t see the post.
If you torque this screw really hard, it’s possible to turn it within the post and misorient the notch. If that problem seems to exist, remove the cell and look at the post. Hold it with pliers and turn the screw so the notch again points up when the post is as high as it will go, tighten the locknut and and leave it in that position for normal use.
For Teleports with slings, serial numbers under TP10-044.
The mirror sling has two purposes. The first is to prevent the mirror from rotating, which would shift the triangles from being centered over the collimation bolts. The second is to lift the mirror up off the lower two cell posts. This provides a nice even support for the mirror and allows the mirror to follow the collimation bolts when they are backed off, rather than being held by friction on the lower posts.
The sling should only apply force to the mirror in a direction at right angles to the optic axis. If it gets taped to the edge of the mirror too close to the back of the mirror, it can tend to lift the mirror away from the collimation bolts That’s because being taped to low causes the sling to have a bend in its middle, as viewed at right angles to the mirror axis. The tension in the sling tries to straighten it, which applies a force to the mirror edge in a direction away from the collimation bolts.
The sling should be straight and parallel to the mirror sufaces when it’s attached with the tape, and the collimation bolts should be backed off before that’s done. This will prevent the tension in the sling from trying to lift the mirror away from the collimation bolts.
The photo at right shows how the mirror is up almost in contact with the top post once the sling tension has been set. With the cell in the scope, you can’t see this clearance, but can still set the correct tension. With the lower right post lock nut loose, when you turn that screw back and forth, you will see that the sling lifts the mirror up and lets it down over a few mm.
The mirror should be held just at the top of this range while tightening the lock nut on the lower right post. The mirror shouldn’t be pushed hard against the top post, but should just touch it lightly. Remember that the sling won’t shorten, but may stretch a bit over time, especially when new. With a properly set up cell, turning any of the three collimation bolts either way should make a positive adjustment of the mirror.
Remember that any primary collimation system has a limited range, and for a Teleport cell it’s about 4 mm: the distance between the mirror cell and the underside of the cell post flanges is about 4 mm more than the combined thickness of the mirror and the triangles attached to it.
This photo shows a side view of the mirror in the cell. Note the clearance between the back of a cell triangle and the cell itself. Also note the clearance between the front of the mirror and the back of the post flange that traps it. The two are about the same, as shown, when the mirror is near the middle of it’s collimation range.
At the forward limit of the range, you won’t be able to turn the bolt any more because the mirror contacts the post flange. At the back limit the mirror just stops moving and if you keep backing off the bolt, it will fall out. Stay within this range by turning the collimation bolts in both directions about equally over time, rather than always one way.
The screws that hold the secondary cage to the top section of the struts should be checked periodically as they may loosen over time with opening and closing the scope. They should not be over-torqued, as that could strip the Delrin anchors. If they continue to loosen, back them out and place 1/4" internal star washers between the screw heads and the flat washers, as provided on the newer units.
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tomnoe@TeleportTelescopes.com |
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© 2002 Teleport Telescopes. All rights reserved. Created Jan 2002 by Linda Silas, The Annex Studios
