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Hornblower
2011-Jun-03, 02:21 AM
I just went through a hair-raising mishap tonight. I dropped my 35-year-old Celestron 8 Schmidt-Cass about four feet onto a concrete slab while setting it up. Except for a slight dent on the edge of the corrector plate cell it appears to have no damage. Only a little tweaking of the collimation of the secondary mirror was needed to put it back in good working order.

To the folks at Celestron back in 1976, a hearty round of applause for a job well done.

RickJ
2011-Jun-03, 08:01 AM
Yes, they made them strong back then. Lucky for us Maybe not today but we only tested a C14 of that vintage as well. Also by accident. Same good result. Though I have heard of broken correctors from such accidents.

I was a supervisor of Hyde Memorial Observatory (http://www.hydeobservatory.info/) for 27 years. Our C14 dates to 1976 as well. The roll off roof is huge and heavy with many large steel support beams. It needs a 5 hp motor to move it. The C14 if not down will be hit by the roof. We never have put a safety interlock switch on it as the concrete was poured before anyone thought of running lines to it for this purpose. One night it happened. The scope is mounted on three half inch bolts that allow its polar alignment. They are embedded in the concrete pier. When the roof hit the upright scope it hit with enough force to break one bolt out of the concrete and bend the others at right angles so the scope was now horizontal and hanging by one bolt as the other still in the concrete was severed. Now that's a blow. Took three to lift the scope and steel pier it attaches to while the remaining bolt was cut. I wasn't there that night so wasn't involved. Whew.

As your scope's experience no harm done. We didn't even find a dent or scuffed paint. How the steel roof could push and slide along the tube as it pushed it nearly horizontal yet not leave a mark we never did figure out. Took some cement work to get the pier back and remount the scope however.

I was worried the same could happen to me as my roof is also steel frame construction but much lighter. Not being in it when the roof is rolled I figured I needed something. So the 14" LX200R has a second surface mirror on its backside. An IR beam hits that mirror and reflects back to a receiver only if the scope is in parked position. It won't budge unless the IR beam is seen.

The roof is frosted plastic that diffuses light. As evening comes on I can point the scope straight up and use that for flats. It is well back from the sloped roof, near center but off set enough to look through the plastic without a center-line seam. So I can raise and lower the scope with the roof closed but it there's only 4" clearance with the scope horizontal when opening or closing. This works very well for flats. Then I park the scope and open the roof to let it come to temperature. One night I did the flats but never opened as clouds rolled in. Next night I went to open the roof. It wouldn't open. Madder than a hornet I went out to find the scope still pointing straight up. Returned and parked the scope. Roof opened just fine.

A couple years later I was trying to close the roof in -40 degree winter weather. Roof can get a bit balky at those temps. This night it wouldn't budge. At that temp sometimes it needs a little tug to get it going so I dressed and went out. It still wouldn't budge. 5 a.m. and snow was coming. Got the wife up and she looked around and asked "Do you really want to close the roof with the scope up like that?" Saved again but I'd been out there for an hour freezing and never noticed it was still up and tracking. A Paramount isn't very quiet. Quite noisy in fact yet somehow I never noticed it was still tracking away. Wife still wonders about my sanity at times.

With the observatory floor 12 feet above ground level and wood it has lots of give. A few eyepieces have hit the deck as as one CCD camera. It has give and no harm was done.

Rick

Grey
2011-Jun-03, 03:46 PM
I've got a C8 of that same vintage as well, and it's held up quite nicely over the years. Except the old fork mount screw threads for the declination fine adjust are stripped (it's my parents', actually, so other folks have used it, but I'm still not sure how someone managed that). Is it worth trying to jury-rig a repair, or should I just figure that after 35 years I should invest in a new mount for it? If the latter, does anyone have a recommendation?

RickJ
2011-Jun-03, 06:32 PM
If Celestron doesn't still stock parts back that far a machine shop could cut a new one.

Rick

Hornblower
2011-Jun-04, 01:43 AM
While touching up the collimation on a star at 200x, I was amused by memories of an ad from a competitor, which cited the Schmidt-Cass as an example of a system which can lose its collimation easily, while extolling the virtues of a scope which can take rougher handling. Mine just took the roughest of rough handling and needed only a slight adjustment, which was easy with the Allen wrench that came with the scope. Normally I go years without having to touch this adjustment.

RickJ
2011-Jun-04, 10:01 PM
The first C10's sure couldn't hold collimation. They'd lose it going from one side of the sky to the other. That was the first "back yard" SCT they made. Prior to that it was a 22 inch. I was at an Astronomical League convention and one amateur brought her brand new C10 (no C8 yet). She complained about collimation. Hearing that Bob Cox went to work on it with great confidence. He was an amazing pro optician and amateur who wrote the Gleanings for ATM's column in S&T for many years. He could fix anything. Except that scope. Bob wasn't one to censor his words and soon the night was full of very foul language. Nothing he did would hold for one swing across the sky. A local University in Nebraska bought one at the same time. It went back to the factory a dozen times before they gave up on it. Fortunately Celestron solved the problem but I wonder if that ad was referring to that time era.

My huge temperature swings require recollimation of my Meade 14" LX200R twice a year. But only one screw need be adjusted and that one is just turned between a summer and winter position, about 20 degrees. I now make the move without "looking". CCDinspector says I hit it within 1" of arc. That is within its measurement error as each image it looks at is slightly different with a different center but always within that 1" of image center. I've done that for several years now.

I've never found collimation of Newtonians to be touchy either. One day carrying my 10" f/8 tube a drunk headed down the wrong one lane ramp right at me. A wall on one side meant I took off across a ditch and through a fence and farm field. I was riding on the ceiling most of the way and had huge bruises from the seat belt (old car, no shoulder belt). The scope and gear went flying as well. 12 volt deep cycle battery ended up in the front seat from the back of a station wagon. Yet the scope was in perfect collimation when set up. I was shaky but the scope was dead on. I never found a need to recollimate after travel. (old late 50's era Cave which I still have). Truss dobs that must be reassembled each time can need adjustment but the well made ones need very little I've found. Usually when I hear a club member complaining about collimation it is really tube currents from carrying the scope in a car that was too warm or cold and the scope still needed to come to temperature. At least in our club collimation gets blamed for far more ills than it is responsible for. While an f/8 is tolerant of miss collimation my 10" f/5 and 6" f/4 are touchy about it and hold very well.

Rick