As some here know I've been working on getting my ancient C-14 (circa 1984) to produce nice round star images in long, unguided CCD exposures. Much of this has been chronicled at http://planet.state.ut.us/slas/patrickw/PATRICKW03.HTML . I've just added a few more pictures (#s 142 to 146). 142 shows a C-5 OTA mounted on the Paramount. It was only on there for one night while I double checked to see that the problem was with the C-14 OTA and not the mount. Happily the mount checked out fine but I had to get the picture as it struck me as funny to have such a tiny, inexpensive scope on a Paramount which is neither tiny nor inexpensive. The other pictures show the C-14 in many pieces (first time I've ever had it apart) with close ups of a few key pieces. Note in image 144 there are 4 set screws sticking out the side of the center tube. I drilled and tapped the holes for those screws tonight and am hopeful that once I get everything back together I'll be able to tighten those screws down to stop the infamous "mirror flop" common to SCTs. Disassembly turned out to be much easier than I thought with the only tools required being a couple of screwdrivers, socket wrench, sledge hammer, regular hammer and a few hex wrenches. I need to pick up some special vacuum grease for the baffle tube (happily Josephine Grahn has a tube I can borrow later today) and I got some flocking paper for the inside of the tube that I still need to apply. With luck I'll have everything back together tonight. Then all I'll need will be some clear skies so I can check and see if my modifications work. Patrick
Very interesting and informative, Patrick. What I'm wondering is, when you put the corrector plate back on, does it have to be aligned any particular way to the mirror? That is, is there a 12 o'clock that has to line up with an equivalent 12 o'clock on the mirror? Or can you put it on in any orientation? I have that question because I keep suspecting that what I did to screw up the optics of my old Celestron 8" was not to get the front on right. But maybe I did something else, like damage the mirror's figure when I cleaned it. It's moot now, because I am using my LX 200 12" but I'm still curious. Best wishes, Joe PS: Thanks to you and Patricia for the nice card. Merry Christmas!
Hi Joe, Chuck here. If you can set up the telescope in front of a test-flat, you can test the telescope optical system as a whole using autocollimation & a Ronchi screen. This would make it easy to rotate the corrector with respect to the primary mirror, and easily see with your own eye if the figure suffered. Ideally the flat should be large enough to test the entire scope at once (full-aperture) but a smaller one will work in a pinch. IIRC, getting the corrector square is more important than a rotational alignment. Did you check for a pencil mark, or engraved fiducial of some kind on the corrector? C. --- Joe Bauman <bau@desnews.com> wrote:
Very interesting and informative, Patrick. What I'm wondering is, when you put the corrector plate back on, does it have to be aligned any particular way to the mirror? That is, is there a 12 o'clock that has to line up with an equivalent 12 o'clock on the mirror? Or can you put it on in any orientation?
__________________________________ Do you Yahoo!? New Yahoo! Photos - easier uploading and sharing. http://photos.yahoo.com/
Hi Chuck, No, I just assumed, hummm, this thing's circular, pop it in anywhere. Then I realized it was impossible to get it collimated. -- Best wishes, Joe
Joe Bauman wrote:
Very interesting and informative, Patrick. What I'm wondering is, when you put the corrector plate back on, does it have to be aligned any particular way to the mirror? From what I've been able to find on the web it only needs to be "close". They
defined that as being within about 20% of the original position. However, it's a simple matter to get it very close by simply marking the corrector and the tube. I've used both magic markers and masking tape in the past. One should use caution when pulling the corrector away from the tube. Every S/C (C-5, C-8 & C-14) I've pulled the corrector off of had three tiny spacers positioned at about 120 degree intervals around the circumference. I understand they do need to go back where you found them. Accomplishing that is no big deal though. You can see them once the corrector's retaining ring has been removed and before the corrector itself is removed. That being the case, one just marks their location with a permanent marker on both the corrector and the inside of the tube (technically one really only needs to mark the corrector *OR* the tube but I mark both just to be sure).
That is, is there a 12 o'clock that has to line up with an equivalent 12 o'clock on the mirror? I could find no mention of the mirror/corrector relationship on the web. But as long as all one is doing is removing the corrector for cleaning the above procedure will work fine.
If the primary mirror is coming out there should be no problem as long as it's left fixed to is back plate since there's only one way to put it back in (Mr. Murphy's laws not withstanding <grin>). However, if the primary is removed from it's back plate then I'd suggest doing as I did and mark the mirror and back plate before removing the mirror from the plate. That way you'll know exactly how to put it back together. To be honest, if I knew then what I know now I might not have pulled the mirror off the back plate. I did that thinking drilling the holes in the central tube would be difficult and I did not want to mess up the mirror. However, drilling and tapping the holes turned out to be very easy and, in hindsight, could have been done with the mirror left on the back plate (though with its front surface protected by tissue paper and a cardboard cover). Bottom line, for me the worst part of taking it apart was my fear that I'd run into all kinds of trouble. As it turns out my fears appear to have been unfounded. It was very easy to take apart and the reassembly, to this point at least, has been equally easy. Patrick
Thank you for a really lucid explanation, Patrick -- things I wish I had known back then. (And to think my son is teaching a lab next semester on optics! I should have known better than just take the telescope apart and put it back together any old way.) How can we as a group keep track of information like this? Any way to set up an electronic filing system that could help the neophyte? My next question is, but what can I do now since I never marked the corrector in the first place? Is there any way to figure how to orient it long after the fact? Best wishes, Joe
Joe Bauman wrote:
Very interesting and informative, Patrick. What I'm wondering is, when you put the corrector plate back on, does it have to be aligned any particular way to the mirror? From what I've been able to find on the web it only needs to be "close". They
defined that as being within about 20% of the original position. However, it's a simple matter to get it very close by simply marking the corrector and the tube. I've used both magic markers and masking tape in the past.
One should use caution when pulling the corrector away from the tube. Every S/C (C-5, C-8 & C-14) I've pulled the corrector off of had three tiny spacers positioned at about 120 degree intervals around the circumference. I understand they do need to go back where you found them.
Accomplishing that is no big deal though. You can see them once the corrector's retaining ring has been removed and before the corrector itself is removed. That being the case, one just marks their location with a permanent marker on both the corrector and the inside of the tube (technically one really only needs to mark the corrector *OR* the tube but I mark both just to be sure).
That is, is there a 12 o'clock that has to line up with an equivalent 12 o'clock on the mirror? I could find no mention of the mirror/corrector relationship on the web. But as long as all one is doing is removing the corrector for cleaning the above procedure will work fine.
If the primary mirror is coming out there should be no problem as long as it's left fixed to is back plate since there's only one way to put it back in (Mr. Murphy's laws not withstanding <grin>).
However, if the primary is removed from it's back plate then I'd suggest doing as I did and mark the mirror and back plate before removing the mirror from the plate. That way you'll know exactly how to put it back together.
To be honest, if I knew then what I know now I might not have pulled the mirror off the back plate. I did that thinking drilling the holes in the central tube would be difficult and I did not want to mess up the mirror. However, drilling and tapping the holes turned out to be very easy and, in hindsight, could have been done with the mirror left on the back plate (though with its front surface protected by tissue paper and a cardboard cover).
Bottom line, for me the worst part of taking it apart was my fear that I'd run into all kinds of trouble. As it turns out my fears appear to have been unfounded. It was very easy to take apart and the reassembly, to this point at least, has been equally easy.
Patrick
_______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://www.utahastronomy.com
participants (3)
-
Chuck Hards -
Joe Bauman -
Patrick Wiggins