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pogobbler
member
Reged: 09/30/08
Posts: 31
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that say their SCT keeps fine collimation for months or years at a time? I could understand if it was permanently mounted, I suppose, but if it's moved around here and there it's just completely out of my experience. I've got a C9.25 and had a C8 in the past and, though I don't abuse them, I find the collimation could at least use a bit of tweaking each time I set it up. I do fine collimation at 470X or 940x with the C9.25" if the seeing permits and try to do the best I can once the scope is cooled down, though the seeing rarely permits me to be sure of absolutely perfect collimation-- though I figure if I get as close as the seeing allows, I'll be able to see all the I can through the limited seeing. Are others not as critical or are the some "super SCTs" that hold their collimation exceptionally well?
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Frank
member
Reged: 01/18/09
Posts: 57
Loc: Netherlands
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My C6 holds collimation pretty well, but my C14 needs a tweak every time I've moved it aroud. I do not have a permanent set-up, so this is evry time I start a session (unfortunately).
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Celestron CGE1400 XLT
C6 XLT
Vixen 6" F5.0 Newton
WO Zenithstar 80 FD
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skybsd
professor emeritus
Reged: 02/01/08
Posts: 604
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Hi,
You didn't comment on exactly what is involved in your setting up, so I can't comment on whether or not your storage, moving, set-up and breakdown is a factor in your case.
I guess I sort fall into that category.
My C-6 XLT and C-14 XLT Fastar DO hold collimation very well - and I do check each time I head out.
That said, my C-9.25 XLT does get tweaked more than the other two, BUT.., that may be due to: -
a] I tend to use the C-9.25 XLT far more than the other two
or
b] My C-9.25 XLT has Bobs Knobs installed
c] Both
But even so, the C-9.25 XLT only ever seems to needs a tweak every 5 - 6 months or so - and there have been occasions where I KNOW I was being anal about what I was attempting to acheive, and made a hash of it.
For all three scopes, I use a Televue 10mm Radian for collimation.
Regards,
skybsd
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4947
Loc: MA
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>>>that say their SCT keeps fine collimation for months or years at a time<<<
Dunno. I touched up the collimation on my C11 every time I set it up, and occasionally several times a night.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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My C11 has to be collimated about 3 times a night.
My C9.25 has to be collimated one time a night.
My C8 has to be collimated about 1 time a month.
My C6 was collimtated 1 time period.
The collimation for all of these is usually no more than a 1/8 turn of one or two of collimation knobs. Most people would probably not even notice it that much but I am just very picky about maintaining perfect collimation all the time.
If I did not have Bob's Knobs on these scopes I am not sure I would collimate this much either. Those knobs make the process so fast and easy that I don't mind doing it. I have it down now to about a 20 second process.
The issue causing all this re-collimation seems to be directly related to the size of the mirror and its ability to shift around. The C11 has the worst problem. I can see now that having a C11 or an ALT-AZ mount would probably be much better than having it on a CGEM. The CGEM can flip it into some pretty weird angles.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2928
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Quote:
that say their SCT keeps fine collimation for months or years at a time? I could understand if it was permanently mounted, I suppose, but if it's moved around here and there it's just completely out of my experience. I've got a C9.25 and had a C8 in the past and, though I don't abuse them, I find the collimation could at least use a bit of tweaking each time I set it up. I do fine collimation at 470X or 940x with the C9.25" if the seeing permits and try to do the best I can once the scope is cooled down, though the seeing rarely permits me to be sure of absolutely perfect collimation-- though I figure if I get as close as the seeing allows, I'll be able to see all the I can through the limited seeing. Are others not as critical or are the some "super SCTs" that hold their collimation exceptionally well?
No scope of any kind, other than an ultra-transportable multi-section Dob, should regularly come out of alignment. My Newtonian has been collimated once in 5 months, when I made a needed modification of the secondary stalk. It's odd how people have learned to tolerate bad mechanics! Usually the problem is readily identifiable and easy to fix with shimming/tighening.
-drl
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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Apples and oranges - That is an alt-az dob not an SCT and you are apparently not transporting it anyplace either.
Unlike an SCT the mirror in your dob is not held in place by a small central grease covered tube, it is held by a sturdy mirror cell. So I am sure it can maintain collimation a very long time.
But try tossing it in the back your car and driving 90 miles, the last 6 of which are on a banged up dirt road leading to a dark site. You wil be collimating all the time too.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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skybsd
professor emeritus
Reged: 02/01/08
Posts: 604
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Hi,
So.., I did qualify with the OP that I could not comment on what their storage, set-up and breakdown is like - reason being that if folks are "tossing it in the back your car and driving 90 miles", then of course it'd be necessary to check, and more than likely tune collimation each time you do that.
My OTAs are all stored indoors in their respective ScopeGuard cases or padded storage units, and get taken out each time for acclimation. After setting up my mounts 20 yards away along the garden, they then get mounted to further acclimatize until my viewing time arrives, when I always begin by checking collimation.
Breakdown at the end is pretty much the reverse of my set up routine.
No tossing, banging, bumping or rolling required - therefore, at least on my scopes, even though I always check (out of habit) I do not need to touch / adjust collimation every_single_time I go out.
Regards,
skybsd
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skybsd
professor emeritus
Reged: 02/01/08
Posts: 604
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Hi,
Quote:
<<snipped>>
If I did not have Bob's Knobs on these scopes I am not sure I would collimate this much either. Those knobs make the process so fast and easy that I don't mind doing it. I have it down now to about a 20 second process.
<<snipped>>
Strange how perceptions differ.
To me, I've always been suspicious of the fact that the only scope of mine that I find needs collimation relatively more than the others is actually the one scope of mine with Bobs Knobs installed - go figure.
Regards,
skybsd
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Al Miller
sage
Reged: 08/25/08
Posts: 417
Loc: San Antonio, Texas
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I rarely, if ever need to collimate my SCT's. The only Newtonian I have at the present is the XT8 Dob. that I have to adjust every time I take it out. The SCT's aren't permanently mounted and don't get banged around much though. My C8 is in a Pelican case that's well padded and my LX200 is on a hand-cart when not in use. The cart makes treks across my yard with some bumps along the way but, I rarely have to adjust collimation. I'm very careful in transporting them, and I check the collimation before each use with a high magnification eyepiece. The LX200 even fell about 15 inches once and hit the ground on its rear end. Even then the collimation was off by "just a hair". Granted, I'll state that the SCT's don't see as much use as the refractors since I mainly use CCD's to image and enhance observing from my moderately light-polluted site.
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Meade 10" LX200 Classic
Celestron C8 XLT OTA
Orion XT8 Classic Dob.
Meade AR-5, f/9.3 refractor OTA (LXD55 version)
Antares 4.1", f/12.4 refractor w/EQ5
Orion 110ED, f/7 refractor OTA
Orion ST120, f/5 refractor OTA
Orion ST80, f/5 refractor OTA (guidescope)
Meade DSIc, DSI IIc and DSI II Pro
Celestron NexImage (x2)
Orion StarShoot autoguider
Atlas EQ-G mount
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Paul G
Carpal Tunnel
Reged: 05/08/03
Posts: 2282
Loc: Freedonia
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I bought my C11 at a time when they were known for not keeping collimation. Company 7 rejected a couple for this reason, another for optical problems, finally got a good one for me. It held collimation very well. We took it out of collimation at the shop, then re-coliimated it with a 5 micron, then a 1 micron star, and it held collimation very well thereafter. I checked it every observing night, had to tweak it every 6 to 12 months.
My scope was an exceptional example, and it also never got banged around, it rode in a cushy car seat on smooth roads. I also never tried to chase its minor mirror flop with collimation.
A friend had a Meade 8" that needed collimation every night; it had a lot of mirror flop as well and didn't seem to be made very "tight."
I guess it depends in part on what one is used to using. When I was shopping for a minivan I test drove the new Ford and it rattled like an old tin can. I mentioned it to the dealer and he said, "All minivans rattle." A couple of weeks later I parked next to a new Ford minivan at a shopping center, asked the owner if it rattled, and he said, "All minivans rattle." I bought a Honda minivan and it never rattled once.
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Gus
Tasco 4.5 Reflector EQ Telescope
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rmollise
Post Laureate
Reged: 07/06/07
Posts: 4598
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Quote:
that say their SCT keeps fine collimation for months or years at a time? I could understand if it was permanently mounted, I suppose, but if it's moved around here and there it's just completely out of my experience. I've got a C9.25 and had a C8 in the past and, though I don't abuse them, I find the collimation could at least use a bit of tweaking each time I set it up. I do fine collimation at 470X or 940x with the C9.25" if the seeing permits and try to do the best I can once the scope is cooled down, though the seeing rarely permits me to be sure of absolutely perfect collimation-- though I figure if I get as close as the seeing allows, I'll be able to see all the I can through the limited seeing. Are others not as critical or are the some "super SCTs" that hold their collimation exceptionally well?
It's not the SCTs, pardner...I gotta say...it's you. 
If your SCT needs to be adjusted every time, examine your procedure. Do you always collimate ONLY by tightening screws? Only if your screw is snug, should you loosen other screws to enable you to keep moving the original screw. Snug good, loose bad collimation wise.
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Uncle Rod
Rod's New Book:
Choosing and Using a New CAT
Available now!
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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I think very few people chase the minor mirror flop with collimation, but I do. It just depends on your tolerance level I suppose. By the way, there is just a layer of grease in there keeping the mirror from shifting around nothing mechanical to prevent the movement. I think my C11 moves more than it should because some of my grease liquified recently and got on my corrector plate. If I opened it up and put in fresh grease I could probably reduce the movement considerably.
As far as Bobs Knobs are concerned I don't collimate any more than I did before I got them. I got them because I found I do like to keep the scope in perfect collimation and it is much easier to do with knobs. With my old Meade 8 sct I collimated one time a year just because I hated collimating. I could see that the stars were not perfect but just ignored it. I simply have a different attitude about it now.
I still haven't really figured out why people think Bob's knobs are any different from the original knobs. The threads are the same, the only difference is the head is big enough to turn with your fingers instead of a hex wrench or screwdriver. So I cannot see what the problem is suppose to be. Some scopes do require nylon washers to use bobs knobs and some do not but those washers can easily be replaced with steel ones if that is the concern. From what I can tell nylon washers do not crush like rubber they are almost as strong as the steel.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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Paul G
Carpal Tunnel
Reged: 05/08/03
Posts: 2282
Loc: Freedonia
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I never tried Bobs Knobs, but since I didn't need to tweak much I was happy with the old fashioned method. My Mak-Cass is permanently collimated, so now I'm spoiled. 
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Gus
Tasco 4.5 Reflector EQ Telescope
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MitchAlsup
super member
Reged: 08/31/09
Posts: 186
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Quote:
My C11 has to be collimated about 3 times a night.
My C9.25 has to be collimated one time a night.
My C8 has to be collimated about 1 time a month.
My C6 was collimtated 1 time period.
My C11 (U11 actually circa 1990) is a little picky about collimation. It holds reasonably well, but there are only about 3 times per year when the skies are good enough to dial it in perfectly. When performing that last little tween of collimation, I only add pressure to the allen wrench without really feeling it move and then back the pressure down. Somehow, what I cannot feel, shows up on the optical surface. The actual movement is far less than 1 degree onthe allen screw/wrench.
My friends C8 (circa 1985) has not been collimated in 20 years and everytime we check, it remains perfect.
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DesertRat
professor emeritus
Reged: 06/18/06
Posts: 665
Loc: Valley of the Sun
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My 1999 C11 with Bobs knobs needs collimation with every use, and again on meridian flip. I think later editions were improved as commented earlier. My 2009 C14 holds collimation very well as does my IM715.
Glenn
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Brandon 94mm f7, Televue TV102 f8.6; GM8
Baader Wedge & Filters, Coronado SM90/BF30
IM715; C11 & C14; G-11 Gemini
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bcuddihee
Pooh-Bah
Reged: 11/04/06
Posts: 1402
Loc: Cincinnati Ohio
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I think that you can snug down the stock screws much tighter than with the hand tightening procedure with Bobs Knobs. My C8 holds collimation very well.
bc
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B Cuddihee
--------------------------
1968 Jason Empire 60X700mm refractor (my buddy from way back)
Celestron Nexstar8SE aka "The Bumblebee",(there is no way this scope should perform as well as it does...but it does)
Feathertouch Microfocuser
Stellarvue 50mm "Sparrowhawk" finder
Denk bino's with Power x switch
Pair of Smart Astronomy 19 EF's (great ep's for binos)
Pair of Edmund 28 plossls
Pair of Edmund 28 RKE'S
Pair of tv 20mm plossls
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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What causes the issue is not the secondary or the screws that adjust the secondary. The problem is with the primary moving around. I think the people who are assuming that bob's knobs are somehow related to the problem of having to collimate more ofter are mistaken. It is simply that the primary is not fixed in one place as it is in a Mak or a Dob.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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Luigi
Post Laureate
Reged: 07/03/07
Posts: 4947
Loc: MA
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>>>only about 3 times per year when the skies are good enough<<<
With a star centered, I dither the focuser very slightly through focus and watch the dancing blob expand and contract, independent of seeing. If it expands symmetrically, it's good. If it expands toward ones side, I adjust the secondary to shift the image in that direction and try again.
Using this method you can tell if the scope is collimated every time you focus when viewing at higher magnification. This generally leads to more frequent touching up of the collimation.
Works on Newts too.
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17.5" f/5 Dob. IM-715 MCT. 120ED. Lunt 60mm Ha.
Zeiss, Leica, Fujinon, Nikon, Pentax, Bushnell bins
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Lane
Carpal Tunnel
Reged: 11/19/07
Posts: 1515
Loc: Frisco, Texas
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Luigi - good explanation - thats how I do it too. This idea that you have to see perfect diffraction rings to collimate is totally wrong. If that was true I could never even do the first collimation of the night since I do that one before the scope has cooled down properly.
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Mounts: CGEM, ORION SIRIUS, AT Voyager/motorized
SCTs: C6, C8, C9.25, C11,
Refractors: TV Pronto, Orion ED80
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