The bear
professor emeritus
Reged: 02/11/08
Posts: 726
Loc: rushville, indiana
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i am trying t get my head around making and using a front mount collmination for both my 6" and 12.5 inch truss type dobs which i intend to  build. i have read quite a bit on here but do not have enough data to figure out how i would adapt one and how they are setup and what parts to use any help would be real nice and pics excellent.
doc
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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mconnelley
super member
Reged: 03/14/06
Posts: 182
Loc: Fremont, CA
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Hello:
I have an idea on how to do this that I'm going to try out. As far as I know, this hasn't been tried before, so it may just fail spectacularly. I'll make a dob with a 6 pole truss. The top of each truss pole will have a 1/4-20 bolt sticking out of it along the axis of the pole. The top end ring will have 3 pairs of angle brackets with slightly oversized holes for the bolts to go through. A pair of wing nuts (one on top and one below) will secure the poles to the brackets.
Here's where it gets weird. You can run the pairs of wings nuts up and down the bolt, which effectively changes the length of the poles. You'll need to change the lengths of poles in pairs. If you choose a pair that meet at the top end ring, then you tilt the top end ring. If you choose a pair that meet at the mirror box, then you end up tilting the mirror box relative to the truss and top end. This is a way you can collimate a truss scope, using the truss poles themselves, from the front of the scope. The catch is that the pivot point is several inches in front of the primary mirror, in the plane of the top of the mirror box. Tilting the mirror box tilts the primary mirror but also translates it a bit. So, after tilting the mirror box, you should adjust the tilt of the secondary mirror. Doing the collimation like this should work, but as I mentioned, I haven't actually tried it yet.
Cheers
Mike Connelley
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Don W
Postmaster
Reged: 05/19/03
Posts: 13171
Loc: Wisconsin, USA
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I believe the word you are looking for is collimation.
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Don Wyman
Obsession 18" f/4.5 #1166
W/Argo Navis DSC and Torus Primary
William Optics Megrez 90
Coronado PST
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Mr Magoo
scholastic sledgehammer
Reged: 11/05/05
Posts: 920
Loc: Franklin, Indiana
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Doc,
Try doing a search here. I know there are several people who have done it. In fact, there is a thread about it active right now. You might look at Jay Scheuerle's Eero ball designs. I'm sure it uses front collimation. Art Bianconi had a thread or two about front collimation with some pictures, although they are probably virtual drawings.
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Ken
Franklin, IN
Member, Indiana Astronomical Society
B.S.A. Astronomy Merit Badge Counselor
6" f/10 Dob
Vintage Sears Discoverer 4-6305A 60mm
Vintage Manon 60mm (The Marsha Scope)
Criterion RV-6
My CN Photo Gallery
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Chriske
Kijkerbouw Urania
Reged: 08/15/04
Posts: 1937
Loc: Boechout, Belgium
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Quote:
Art Bianconi had a thread or two about front collimation with some pictures, although they are probably virtual drawings.
Yes indeed, they were virtual drawings only and not tested.
Anyway, I would not do this collimation with the trusses itself. The rotationpoint of the collimation-movement is not at the centre of the mirror or it's axis, but at the side of the primary cage. Very difficult to achief proper collimation tuning the trusses and collimating the scope at the same time imo...
Tuning the scope with the lower trussnuts will move the trusses at the base just a tiny bit, but the secondary cage will swing a large amount risking loosing sharp image 'out of focusrange'. Especially with lowprofile focuser not feasible I think.
Why not use a frontcollimation system instead...?
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Chris
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jpcannavo
sage
Reged: 02/21/05
Posts: 305
Loc: Long Island New York
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The basic principle of front-collimation - as used in my previous Royce 16 and my current ZOC 16 - involves moving the collimation mechanism to the corners. In the picture below you see the back of my old mirror cell for the 16 Royce conical. The collimation mechanism involves short threaded rods mounted in a ball bearing movement at the corners of the cell. These then thread into taped nylon "bolts" in the corners. The ball bearing mechanism is not quite visible in the photo. Instead you can see the two bolts in each corner mounting the flanged ball bearings. Note removable "briefcase" style assembly mirror cell for the Royce conical.
Note the array of 8 bolts (barely visible) in the center plate, is to mount the aluminum stud (not visible) which mounts the conical mirror by way of its central perforation.
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Joseph Cannavo
16" F5 Zambuto, front collimating, scope nearly complete - WSP here we come!
16" F5 Royce, conical blank, front collimating (Mirror Sold)
10" F5 Dob
Mid 70's RV-6
4" Orion 100mm ED
Mr Keeyoots (My Cat)
Edited by jpcannavo (10/04/08 01:19 PM)
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jpcannavo
sage
Reged: 02/21/05
Posts: 305
Loc: Long Island New York
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This is a corner view of the cell attached to the mirror box. See my badly drawn arrow. This points to the threaded rod traversing the gap from the mirror briefcase to the steel cell, into the ball bearing assembly...
Edited by jpcannavo (10/05/08 07:47 AM)
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jpcannavo
sage
Reged: 02/21/05
Posts: 305
Loc: Long Island New York
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This shows the inside of the mirror briefcase, minus the steel cell. What is left is one of the (four)threaded rods running in the upper and lower corner mounted tapped nylon tracks(painted black), and the ball bearing assembly at the end, removed from the corners of the mirror steel cell...
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Joseph Cannavo
16" F5 Zambuto, front collimating, scope nearly complete - WSP here we come!
16" F5 Royce, conical blank, front collimating (Mirror Sold)
10" F5 Dob
Mid 70's RV-6
4" Orion 100mm ED
Mr Keeyoots (My Cat)
Edited by jpcannavo (10/04/08 12:48 PM)
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jpcannavo
sage
Reged: 02/21/05
Posts: 305
Loc: Long Island New York
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This pic shows the inside of the upper mirror box with the inner guides for the aluminum collimation rods that attach to the threaded rod mechanism in the corners of the briefcase/mirror cell assembly. At the bottom you can see the edge of the mirror with a black mirror cover in place....
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Joseph Cannavo
16" F5 Zambuto, front collimating, scope nearly complete - WSP here we come!
16" F5 Royce, conical blank, front collimating (Mirror Sold)
10" F5 Dob
Mid 70's RV-6
4" Orion 100mm ED
Mr Keeyoots (My Cat)
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jpcannavo
sage
Reged: 02/21/05
Posts: 305
Loc: Long Island New York
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And this is the view of the front collimating 16" Royce conical scope as a whole. Note the three (out of four possible) aluminum collimating rods in place. Yes, I used a four corner - over constrained - mechanism. This allowed me to keep things under just enough tension to take up any play. Adusting any two adjacent rods, however, gives smooth adjustment around either the x or y axis. The entire mechanism was extremely successful. No collimation shift, and easy tweaking at EP by star test for High power views. I no longer own this scope, but have adapted a similar mechanism to my ZOC 16. The difference here will be a three corner (as opposed to four) mechanism.
Sorry to highjack the thread - but I felt it was relevant.
I will have a dedicated thread for the ZOC16 in about one week - or less.
Bottom line for me. I'll never go back to conventional collimation again!
Joe
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Joseph Cannavo
16" F5 Zambuto, front collimating, scope nearly complete - WSP here we come!
16" F5 Royce, conical blank, front collimating (Mirror Sold)
10" F5 Dob
Mid 70's RV-6
4" Orion 100mm ED
Mr Keeyoots (My Cat)
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jpcannavo
sage
Reged: 02/21/05
Posts: 305
Loc: Long Island New York
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One more view, with mr Keeyoots...
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Joseph Cannavo
16" F5 Zambuto, front collimating, scope nearly complete - WSP here we come!
16" F5 Royce, conical blank, front collimating (Mirror Sold)
10" F5 Dob
Mid 70's RV-6
4" Orion 100mm ED
Mr Keeyoots (My Cat)
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Denis
sage
Reged: 12/24/05
Posts: 217
Loc: Rennes, France
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A nice solution on the strock 250. You can see it at the middle of this page :
http://www.astrosurf.org/magnitude78/Strock-250/T250_Fabrication.html
Two pictures of my front collimation system on my 14" split ring :
That's a two points collimation and the third may be set from the rear if necessary(never happened)
Another one from my 10" lightdob, using two levers and pushing screws to move the triangles :
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Canon 10x42 IS binoculars.
Meade sc 4" on homemade fork equatorial mount.
homemade 10" an 14" dobsonian
Nikon photogear.
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The bear
professor emeritus
Reged: 02/11/08
Posts: 726
Loc: rushville, indiana
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interesting ideas i will look further and hope for more posts also. still having some difficulty wrapping it in my mind i have used the search function but drew up several hundred posts using "front collmnation" as a search term perhaps it is the wrong one?.
doc
i have also read some threads on the subject perhaps someone has a link or two for further clarification for me.
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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RossSackett
sage
Reged: 08/17/07
Posts: 322
Loc: Memphis, TN
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I just did front collimation on as 12.5" 6-pole truss I showed at Stellafane this year. Check my flickr page below for some pictures.
Ross
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Ross Sackett
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11 scopes currently on the flight line from 4.25 to 18"; 5 pairs of astronomical binocs 35-80mm. My wife suggests that with just one pair of eyes, this might be excessive.
See my scope pix at http://www.flickr.com/photos/8315630@N04/
Carpe noctem!
Amateur astronomer = A mature moon-starer
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jpcannavo
sage
Reged: 02/21/05
Posts: 305
Loc: Long Island New York
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James
Any particular aspect that are you wrestling with?
BTW, As for search terms, also try variations on eyepiece accessible collimation. The reality though is that - I think - there are only a handfull of examples out there, some of which you vae seen here. Here are a couple more:
http://www.scopemaking.net/hrv/cald.htm
http://bi-staff.beckman.uiuc.edu/~melockwo/telescopes/16in_F4/16in_F4.html
It really is surprising that more scopes are not designed this way.
Joe
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Joseph Cannavo
16" F5 Zambuto, front collimating, scope nearly complete - WSP here we come!
16" F5 Royce, conical blank, front collimating (Mirror Sold)
10" F5 Dob
Mid 70's RV-6
4" Orion 100mm ED
Mr Keeyoots (My Cat)
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The bear
professor emeritus
Reged: 02/11/08
Posts: 726
Loc: rushville, indiana
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okay these links answered my questions so far pictures and drawings speak better than text for some reason. thanks guys
doc
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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StarDusty
member
Reged: 10/02/07
Posts: 76
Loc: Belmar, NJ
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I recently built a 16" Truss Dob with top side adjustment points to collimate the scope as shown below. (This is one of the progress photos before the mirror cover deck was installed) It works fine. The cell is a little ususal and very light, using a tee concept with adjustment at the ends of the tee. It also works fine.
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The bear
professor emeritus
Reged: 02/11/08
Posts: 726
Loc: rushville, indiana
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StarDusty would it be possible to get some close ups of those adjustment points and how they connect to the mirror cell?. also on the (top side) adjustment points what did you use on the top part. i have a question, could someone use plastic gears on the collmination bolts used to move the cell and the long adjustment shafts of whatever length required for eyepiece use. or do the gears need to be super tolerance gears, like machined parts. something like what RossSackett did on his and i like what Denis, jpcannavo
did on the extensions for the adjustments. i think i am getting the gist of what i need to think about when i design these mirror cell's and scopes i know KISS plays well here but i want it to be stable and hold its collmination. i need to think about this more and put something to paper and or computer design.
i thought about using electronics and had some very good people send me their ideas as well as working concepts but i do not want to rely just on electronics perhaps maybe using both manual and computer aided. my mind is starting to wake up thank you gentlemen and ladies.
doc
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Longitude -85.42786 Latitude 39.59153
when all else fails use duct tape "works for me"
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jayscheuerle
Carpal Tunnel
Reged: 01/16/06
Posts: 2958
Loc: S. Philadelphia, PA
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Here's some construction shots of a 6" f/5 ball-scope.
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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jayscheuerle
Carpal Tunnel
Reged: 01/16/06
Posts: 2958
Loc: S. Philadelphia, PA
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2
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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jayscheuerle
Carpal Tunnel
Reged: 01/16/06
Posts: 2958
Loc: S. Philadelphia, PA
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3
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12" Green Goblin (trusser w/Protstar secondary and OWL refigured primary)• 6" f/5 Eero2 ball-scope • 6" f/5 Frankenscope • Garrett Optical 10x50 binos • Edmund 8" yoke-mounted red-tube reflector • Edmund 6" GEQ red-tube reflector (on loan to Dad)
Gone, but with lessons learned:
Skyquest XT8 • NexSTar 8i • Eeroscope 6" f/5 ball(sacrifice was not in vain) • Vixen ED80sf • Edmund red-tube 4.25" f/10 • Edmund Astroscan
Facts are stubborn things.
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Jim Romanski
sage
Reged: 01/02/05
Posts: 479
Loc: Guilford, Connecticut
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Here are a couple of additional ideas from a very recent thread: Mirror Cell Rebuild...front collimation
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Jim
17.5" Dob "Project"
13.1" Coulter
8” Cave
NP 101
25x100 binos
Naglers, etc.
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