dvb
Carpal Tunnel
Reged: 06/18/05
Posts: 1761
|
|
My sweet little C8 had very good collimation, just a touch off. I decided to treat it to some Bob's Knobs. Followed the instructions that came with the package: checked the concentric pattern of the optics, changed one screw at a time. Did a rough adjustment to achieve the concentric pattern again. Took it outside to true it up on Arcturus. Use a 10mm EP to get 200x.
What a mess! A comet flaring off to the left from a point of light that looks like it was drawn with a Spirograph.
Adjusting the knobs just pushes the whole image around in the view, without altering the position of the black spot that sits in the lower left of the defocused image.
I guess it's back to the drawing board -- and possibly back to the original screws. I've read the thread below about different instructions for installing the knobs; unfortunately, they come too late for me.
 
--------------------
I'll take one of each, please:
Skywatcher 10" f/4.7 Newt on Matilda
Celestron 8" SCT
Meade 8" SN f/4
Celestron C6 SCT
Skywatcher ED100 f/9
Skywatcher ED80 f/7.5
EQ6 Pro "Matilda"
Skymaster 15x70
Minolta 10x50
Mallincam HyperColor Plus
Speco 9" CRT
|
amys
Carpal Tunnel
Reged: 06/12/06
Posts: 1708
Loc: Groton, CT
|
|
Bummer. Installing the knobs was a huge mistake on my Mak but for a different reason. Aside from the fact that collimation was way off, I couldn't turn them easily. In fact, I tore up the skin on my fingers trying to turn them. I have reinstalled the factory screws, which turn quite easily.
But if I were you, I wouldn't give up on the knobs just yet, since the ones made for SCTs really are easier to use than the screws. I found that using Robin Casady's daytime method when collimation was way off got me very close so that I only needed to do minor tweaks on a star to get it perfect.
www.robincasady.com/Astro/myimages/collim.html
Worth a try?
--------------------
Amy
|
Keith Howlett
professor emeritus
Reged: 03/06/07
Posts: 686
Loc: Northumberland, UK
|
|
Hi dvb,
Sorry to hear you've had a bad time with Bob's knobs, I found them very good with my old LX200. Once I had the scope back into collimation it was reasonably easy to keep it there. Like you I started with the concentric view through the tube and carried on tweaking it at night. (IIRC replacing one screw at a time is just intended to stop the secondary mirror from heading off down the tube rather than helping preserve collimation.)
Best of luck,
Keith
--------------------
14" f10 RCOS / AP1200
AP 105 Traveler / AP400 QMD
Coronado SM90 Filter
|
rmollise
Pooh-Bah
Reged: 07/06/07
Posts: 1357
|
|
Quote:
I guess it's back to the drawing board -- and possibly back to the original screws. I've read the thread below about different instructions for installing the knobs; unfortunately, they come too late for me.
Here's a hint:
When you're initially examining the optics to see if they look "concentric," be sure you're standing at least 6 feet away and are looking dead on.
Outside, use Polaris and start with the rough collimation routine (way out of focus donut).
You can make things easier to figger by using the simple technique of putting the "squished" side of the donut on the field edge and turning the knob(s) that move the donut to the middle of the field. Repeat as needed and move on to fine collimation.
Bob's Knobs do work and really are a god-send.
Let me add that I ran into a young feller down Chiefland way in the same fix. Took us all of about 10 minutes to set things right. So...keep after it.
--------------------
Uncle Rod
Watch for Rod's New Book:
Choosing and Using the New CATs--coming soon!
Edited by rmollise (05/16/08 04:24 PM)
|
conus
Carpal Tunnel
Reged: 10/12/03
Posts: 2974
Loc: OC, Calif
|
|
Don't give up. Really. You will get the hang of it, and when you do it will make the process much easier. You'll love it.
--------------------
Steve R.
12" Orion XTi
Fujinon 10x42
Oberwerk 12x60
My toUcam Images
|
rick rian
The Lockster
Reged: 08/03/04
Posts: 13250
Loc: SE Minnesota
|
|
Keep trying ... Bob's Knobs have been a great improvement to the collimation process for me. When I first installed mine I had the same experience. Honestly, it took about 10 minutes to make things right. Hang in there.
--------------------
Rickster
NexStar 8i, TV85, Canon 15x50is
Time is precious, waste it wisely.
|
cheepnis
super member
Reged: 02/16/08
Posts: 178
Loc: New York
|
|
The knobs are fine, you are just WAY out of collimation.
Start the process with your lowest mag ep and work your way up.
Good luck...
-Tim
--------------------
"...through the transitive nightfall of diamonds"
Orange Tube C8 (1978?) orig Fork Mount
Ultima 8
C80-ED
CG-5
Nexstar SLT
Various gagets and gizmos to go with.
NELM in my backyard like 4 on a GOOD night 
|
WadeH237
sage
Reged: 02/24/07
Posts: 310
Loc: Snohomish, WA
|
|
You've had some good advice here.
To add to that, if the donut looks centered, but turning the knobs doesn't affect it other than to move the whole image around, then you are probably too much out of focus.
Try getting closer to focus and see if you can see the donut hole so it's off center. Also, as you are fiddling with getting rough collimation done, be sure that you are just tightening the knobs and loosening them too far.
And don't panic. What you are seeing is completely normal for a scope that's out of collimation (when the stars are close to focus, they look like little boat anchors to me.) Once you've done collimation once or twice, it'll be a breeze.
Thanks,
-Wade
--------------------
Stuff
Visual Stuff (shared with wife and kids, 10 & 12): Celestron Nexstar 5, Generic 6" F/8 Dob, Celestron C6 or C8 on ASGT mount, CGE-1400, Coronado PST, 12x70 Binoculars.
Imaging Stuff: Meade 8" LX200ACF with Optec TCF-S focuser on CGE mount, SBIG ST-10XME with CFW8, Astrodon filters, Canon EOS 20D.
|
tk89123
super member
Reged: 03/13/07
Posts: 133
Loc: Las Vegas, NV
|
|
Listen to what Uncle Rod tells you, he is THE Cat Man. If he says it, you can bet money on it. Keep working with the collimation, you'll get it right. I would suggest that you try to screw the knobs all the way in until they just start to get a little tight and then adjust your collimation by slightly screwing out so that you don't risk dropping the secondary by unscrewing the knobs too much.
--------------------
"My God, it's full of stars!"
Tom Kilgore
Las Vegas, NV
Meade 8" SCT 2080B
Orion 102mm Apex Mak
Meade 114mm F8 Newtonian
|
dvb
Carpal Tunnel
Reged: 06/18/05
Posts: 1761
|
|
Thanks, all, for the sympathy and suggestions.
What I have done is taken my 2" Jim Fly sight tube -- just a hole in the end and crosshairs. Positioning myself about 6' back, looking through the sight tube, I can see that things are out of adjustment in a way that would have shown the star test I saw last night.
So, it won't be a 10 minute procedure, but I have a plan! 
--------------------
I'll take one of each, please:
Skywatcher 10" f/4.7 Newt on Matilda
Celestron 8" SCT
Meade 8" SN f/4
Celestron C6 SCT
Skywatcher ED100 f/9
Skywatcher ED80 f/7.5
EQ6 Pro "Matilda"
Skymaster 15x70
Minolta 10x50
Mallincam HyperColor Plus
Speco 9" CRT
|
Rusty
Postmaster
Reged: 08/06/03
Posts: 16107
Loc: Brooker, FL
|
|
Welcomoe to Cloudy Nights!
You're onto IT - Bob's Knobs don't create a problem, they solve it. What they do do is make the solving issue much easier.
--------------------
N11GPS Fastar
TOA-130S
MK66 Std
Vintage C5
Megrez II 80mm ED Triplet APO
SolarMax 40
NJP Temma II
Sirius EQ-G
ST8XE/CFW-8 (LRGBHa)/AO-7/DF-2/STV/ST237a/350D (Unmodded)/Mallincam Color Hyper Plus/DSI III Color
Two not-spoiled Golden Retrievers - Maggie and Casey
Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering. - Arthur C. Clarke
|
Muffin Research
scholastic sledgehammer
Reged: 09/28/07
Posts: 758
Loc: Belgium
|
|
Bob Knobs are okay as they are so much easier to get collimated but what I noticed on the C8 is that now I got bob knobs I Can collimate more easily but the collimation is thrown off much faster.
With the original screws the collimation stayed on much longer.
However I feel a lot better not having to fidget with an allen key near the corrector plate in the dark.
--------------------
Quelle Horreur!
Requime pour un Twister.
|
rmollise
Pooh-Bah
Reged: 07/06/07
Posts: 1357
|
|
Quote:
Bob Knobs are okay as they are so much easier to get collimated but what I noticed on the C8 is that now I got bob knobs I Can collimate more easily but the collimation is thrown off much faster.
With the original screws the collimation stayed on much longer.
However I feel a lot better not having to fidget with an allen key near the corrector plate in the dark.
The Knobs should make absolutely no difference here. As always, be sure you collimate by TIGHTENING. Only when a knob is snug should you loosen an opposite number or numbers to continue moving in the proper direction.
--------------------
Uncle Rod
Watch for Rod's New Book:
Choosing and Using the New CATs--coming soon!
|
Muffin Research
scholastic sledgehammer
Reged: 09/28/07
Posts: 758
Loc: Belgium
|
|
hmm I feel the originals screws were much stiffer in their socket than the bob knobs, you had to apply a lot of pressure with the allen key to turn them.
with the Bknobs it's very very easy to turn.
and I'm guessing vibrations & bumps will have more effect on the bob knobs then on the original screws.
--------------------
Quelle Horreur!
Requime pour un Twister.
|
Bob Griffiths
Post Laureate
Reged: 10/10/05
Posts: 3948
Loc: Frederick Maryland
|
|
The problem I personally have with Bobs Knobs is that I have fat fingers and my touch is nowhere near as "firm" as it is using a screw driver.. in other words my fingers may move 1/16th of a turn yet the knob has not moved at all....
Not a big problem in any case as I got used to the "feel"...
BUT once tightened the Knobs "hold" just as well as the original screws.. no difference at all...
Bob G
--------------------
CPC1100
Nexstar 8i + GPS & Rays Brackets
Denk S1 power switch
Orion 100 mm Refractor
Meade LXD 55 ...AR-5 127 mm Refractor
Exploradome Observatory S.I.E. (Smiling Irish Eyes)
39*21'03" N
77*28'12" W
|
cheepnis
super member
Reged: 02/16/08
Posts: 178
Loc: New York
|
|
On a C8 the secondary is mounted on a steel plate, and that is what the collimation screws are threaded into.
As Uncle Rod states you finish the collimation by tightening, have no fear of over-tightening when using Bob's knobs (You should be careful if using an allen wrench though, more so for stripping threads or torquing off the head).
Tight tight tight.
I only undo a screw when beginning a rough collimation. As a result I haven't undone a screw on my Orange-tube since I installed the knobs about 5 years ago.
-Tim
--------------------
"...through the transitive nightfall of diamonds"
Orange Tube C8 (1978?) orig Fork Mount
Ultima 8
C80-ED
CG-5
Nexstar SLT
Various gagets and gizmos to go with.
NELM in my backyard like 4 on a GOOD night
|
rmollise
Pooh-Bah
Reged: 07/06/07
Posts: 1357
|
|
Quote:
hmm I feel the originals screws were much stiffer in their socket than the bob knobs, you had to apply a lot of pressure with the allen key to turn them.
with the Bknobs it's very very easy to turn.
and I'm guessing vibrations & bumps will have more effect on the bob knobs then on the original screws.
The original screws ain't "stiffer." If collimation isn't holdin' you don't have the knobs snug enuff.
--------------------
Uncle Rod
Watch for Rod's New Book:
Choosing and Using the New CATs--coming soon!
|
Muffin Research
scholastic sledgehammer
Reged: 09/28/07
Posts: 758
Loc: Belgium
|
|
okay, i'll try
--------------------
Quelle Horreur!
Requime pour un Twister.
|
southmike
Carpal Tunnel
Reged: 11/22/04
Posts: 2819
Loc: Fayetteville, NC
|
|
I never liked bobs knobs.. they seem to need more frequent collimnation, and can be a buger to install, and really through your collination out.
course I don't like the whole reacing aroind glass with metal objects ether but my scopes rarely need to be collimnated....just my two cents most people are happy with theirs.
like the other users said your collimnation is prob just way off.. a lil goes a long way.
--------------------
group scope pic
my refractors
LX200 10"-St120
LX200 8" f6.3-Orion 80ed
LX200 8" f10-Orion 90 Mak setup pic
Meade 102ED LXD650
Sky Watcher 100 ED Triplet prototype
Nexstar 5
etx125
etx70's
|
skj
member
Reged: 04/13/07
Posts: 98
Loc: McKinney, Texas
|
|
Quote:
The original screws ain't "stiffer." If collimation isn't holdin' you don't have the knobs snug enuff.
Any worry of overtightening on a C6? I find my collimation shifts slightly when I move from say eastern sky to western sky even though the knobs are a fairly tight. I've been afraid of cinching them down any tighter... it's pretty easy to just re-collimate on a new star.
--------------------
Steve Johnson
Celestron C100ED Refractor
Celestron C6 SCT
SkyView Pro Mount
Free access to God's amazing creation
|
Previous
Index
Next
Threaded
Edit
Reply
Quote
