Telescope Reviews: tube question

Hello Andy!

>>> The cost of having an aluminium tube made with no seam is the welding. They have to make a Jig to hold the seam in place which is labour intensive.

Get someone to roll the tube for you only.<<<

Thanks... that's a VERY useful bit of information!

In every design, eventually there comes compromise... and the nice, neat welded seam appears to be biting the dust on this one.

Perhaps it would be helpful if I outline just exactly what I'm trying to do here.

Instead of saying I'm BUILDING a telescope (an idea I've toyed with for a very long time), it might be more accurate to say that I'm trying to REDESIGN and REBUILD a telescope; convert a sow's ear into a faux silk purse, as it were.

Enter EBAY... America's overstuffed attic!

For the last couple of weeks, the folks over at Galileo Telescopes have obviously been parting out their battered display models from the trade show circuit and scopes that got creamed in shipping, and putting the debris on EBAY.

Among the stuff that appeared was an intriguing package; the cell, mirror, spider and diagonal from one of their FS-135 telescopes (mirror is 135 MM with an 1100 MM focal length, about an F 8.1). The whole package went for the princely sum of $40.00.

At the same time, I also grabbed a so-so GEM, and a declination drive motor, also for bargain basement prices.

Armed with a copy of STANDARD HANDBOOK FOR TELESCOPE MAKING, and using the NEWT telescope design software, I think I've been able to reverse engineer this FS-135 beastie.

Galileo is, I gather, just a few cuts above the Toys-R-Us telescopes. However, the cell and spider seem to be fairly substantially made. Mirror grinding and polishing are no doubt machine mass produced; it may or may not be too bad. That remains to be seen; if testing shows that it's too outrageous, the primary is at least a rough formed hunk of glass that can be stripped of coating and refigured into something better.

I'm envisioning an El Cheapo telescope with minimal effort, and hopefully MY engineering and care in construction will cut less corners cost wise and be better than the Galileo assembly line product.

Anyway, because of the cell and spider, I'm married to a 6.625" diameter tube on this project. I haven't been able to find out for sure, but I get the impression that Galileo based their telescope on PVC sewer pipe; an offense to the soul of any engineer, but a delight that warms the cold hearts of the front office Bean Counters, who are only concerned with the unit price of every telescope going out of the door!

In any case... for this telescope design novice, job #1 at this point is to come up with a tube design with enough rigidity to hold the optical chain in some sort of alignment, and stiff enough to make vibration from external stimulus fall into the high frequency (and small amplitude) realm.

Maybe I'm full of fecal refuse on this... but so far it's been an interesting project for a Newbie.

Mr. T.

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Owner & operator of the Mahon Loomis Memorial Radio Monitoring Station & Retirement Home for Ancient Irish Setters

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