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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3459
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Curt- the previous answer was so long, I wanted to answer this seperate question seperately. (I was afraid C/N might explode if I made my answer any longer! 
Quote:
Here is the problem with using a laser as you've suggested - I can't actually see into the focuser enough to see if the laser is retracing on itself. My focuser is centered at a point 6" down from the tube front so I don't have line of sight on the laser's front end sitting in the drawtube. Maybe I need to hold a mirror down there so I can see what's going on as I rotate the secondary...?
That would work- so long as you are careful to not shine it back in your eyes! One of these inspection mirrors on a stem- like a dental mirror or that mechanics to use to see around corners such as this.
Perhaps an even easier way would be just to cut a 1/2"- or even a little smaller hole in a sheet of paper... and place it over the focuser hole- so the laser beam is coming out the center of the hole. Now, you will be able to see on the paper where the returning laser beam is, and adjust the primary until it's coming right back through the hole- and this will get you close enough that you will be able to find it in the 45* cutout of the laser collimator. Once you get used to it, you'll find it quick and easy to do- and your alignments will just be touch-ups each time you use it, rather than full alignments. It looks like your scope is solidly built, so I wouldn't expect to see much change each time you use it. Getting it set up properly initially will be a good teaching tool for you, and you'll soon find collimation really isn't so difficult after all! The only thing you should have to do is a star test for final confirmation of all your work to this point- and perhaps a final touch-up.
Good luck, Curt! Again- NICE scope! Certainly took you a lot of math and calculations to get to this point- now time to enjoy it!
Best~
Wes
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Wes, I can't thank you enough for your time and suggestions. One uber post deserves another! Here I go, one at a time.
First of all, a massive brain fart occurred when I wrote my previous post. I actually do have a 45º laser accessory that Howie Glatter sold me when I purchased my 2" laser. It's an extender tube that places the collimator entirely outside of the tube, which is essential in my case because I can't see what I'm doing while turning knobs down at the mirror-end otherwise. Somoehow I didn't think about this which is embarrassing. I definitely should be able to see that beam return to the element if I use this accessory.
I totally understand the need to ensure the laser is true within it's own casing. One of the reasons I bought a Glatter laser is that they are supposedly maintenance free. My previous collimator was a real *BLEEP*. It literally had a laser pointer inside a metal tube, with three screws that pitched it around. Trouble was, if you pitched it too much the button on the pointer became misaligned with the button on the outside (literally a button pushing a button). I got rid of it and bought the Glatter. Now, I've not proven it to be true though, so I need to do that, but in defense of the Glatter laser, it doesn't even have adjustment screws on it. So I guess if it isn't true to the casing then I'll have to call Howie, lol.
So operating under the assumption that my Glatter laser was in fact truely alligned, I spent some time squaring my focuser to the tube. But, my method wasn't as good as what you described. I had a piece of cardboard spanning the insdie of the tube with a hole punched dead center. Cardboard can bend though, whereas your paper trick has less error involved IMHO. I did use that method for marking square rows of holes around the tube, but I never realized you could use it for squaring a focuser too with some additional steps. Makes perfect sense to me. I'm gonna to do this asap, right after I confirm that my Glatter laser is deadeye.
I still don't understand why rotating the secondary wouldn't move the beam off the primary's center mark (asssuming all other alignments are done). It's a 45º, true, but it seems like pitching it in the other axis (i.e. rotating) would move the beam off the center mark below. I don't know, it doesn't matter I guess.
Well thanks again. I have more to run with at this point than ever before. When I started this project I knew I wanted a newtonian for imaging, and several reasons influenced that. Bang-for-buck is usually my preferred course of action. But with that said, I will always look at my fellow imaging friends who use refractors and be jealous of their virtually maintenance free telescopes. Collimation, IMHO, is the single greatest compromise to be made with reflective optics. Everything else is peaches for me though 
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3459
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Curt-
You're welcome. Happy to help! Anyone who's put all the effort into a project that you have- and had it come out so nice deserves any help he needs- and also, a pat on the back!
Re. laser alignments- I have an Orion... nothing fancy- the laser in a tube with the switch against a switch- but it's accurate, and to me- that's all that matters. I didn't have to tweak it at all. But I can if I need to! The biggest problem was when I left it home one night- and had to borrow one from someone else to align my f/27 schief! The thing is, if you check it you KNOW. No questions. I agree- Howie's products are top notch. Test it- and you'll be certain, and feel better for knowing for yourself.
Re. rotating the secondary- try it while you're playing with it. Look at the primary while you rotate the secondary a little bit- then look at the returned beam on the side of the tube. All of a sudden, a little light will click on in your head- and you'll go "Hey, o.k., now I see!" Even if it's off in rotation a bit, it's still a 45* pointing down. The return path, however, is a different matter.
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But with that said, I will always look at my fellow imaging friends who use refractors and be jealous of their virtually maintenance free telescopes.
First of all, Curt- once you get the hang of collimating it- you'll find it to be very simple. Just a quick and easy alignment. A WHOLE lot easier than all the photo work you're doing! That's the stuff I don't understand!
Remember... your friends with their cookie cutter refractors- they , in turn, will be looking at you , thinking- "Man, what a beautiful and cool scope that guy has. There's not another one like it, and it works sooooo good. He really has a scope to be proud of."
People look at their scopes and say "How much did that cost?"... people will look at yours and say "You mean you made that yourself???? You're kidding!, right? "
And that , my friend- you can't buy.
Wes
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3126
Loc: Northeast
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You don't have to use an additional mirror to see the end of the laser's aperture- just look at the reflection of the secondary off the primary. You'll see the laser's aperture there in the secondary image. Touch the laser, or focuser, and look for an errant dot wiggling/moving slightly outside the stream of dots; that's the returning reflection that is the one you should be concerned with. Tweak the primary so it falls within the laser's aperture. Beware if you're dislexic, it could get confusing otherwise. You might have to collimate twice if it's really far off to start with.
Mark
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So many projects, so little time!
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3459
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DOH! GOOD point, Mark... never thought of that!
The one caution I failed to add is to always be extremely careful when looking down your scope tube to not let the laser come back in your face/eyes if its missing the secondary altogether..
Wes
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 569
Loc: Riverview, FL, USA
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Curt,
Congratulations on producing such as a great telescopic instrumnent. I am sure it will serve you well based on the images it has produced thus far. Your time and effort has truly paid off. Kudos in abundance, my friend!
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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deSitter
Carpal Tunnel
Reged: 12/09/04
Posts: 2926
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Has anyone ever thought of putting a small hole directly opposite the focuser - one that is usually plugged - but can admit the laser beam or matched up with a cross hair and so ensure the correct placement of the focuser? (done of course with the secondary removed).
It would be just a matter of care to get the hole absolutely directly opposite the focuser.
-drl
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3459
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Quote:
It would be just a matter of care to get the hole absolutely directly opposite the focuser.
That's why- if building a scope from scratch, I like to mark the focuser hole with a 1/16" hole on center, do the paper wrap thing and mark/drill the exact opposite side of the tube at that time before then enlarging the focuser hole. It enables me to easily mark a spot exactly opposite the focuser. With an existing focuser hole, I've laid a strip of masking tape crosswise with the edge across the center of the hole as best as I can- then measure/mark a dot in the center of the tape to aid in measuring.
Wes
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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Thanks everyone for the ongoing kind words.
I wish I'd thought of the idea to drill a holw opposite the focuser. Now the tube is powder-coated I probably won't attempt to do this, but rather I'll go with the paper method Wes suggested.
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3459
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Curt-
Even though the tube is powdercoated, you still could do that... easiest way to be certain the focuser is square. You could use a dremel hand grinder to grind a tiny spot instead of centerpunching it, to avoid any damage to the powdercoating- get enough of a dimple to start a hole... we're only talking a tiny hole.... but I do understand your reluctance. If it were me, I'd rather be certain my focuser was square, especially for astrophotography work.
Wes
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imhotep
Pooh-Bah
Reged: 02/14/07
Posts: 1429
Loc: Tampa, FL
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You're right it's doable, but there's one more detail. I'm going to install a flocked tube liner which has about a 1/8" air gap between the inner tube wall and the flocked tube liner. Transferring a hole from the metal tube perfectly straight onto the liner will be a challenge, but I'm going to think about it. Transferring mounting holes for the spider and mirror cell is important to be as accurate as possible, but if it's off a little bit then the liner get's shifted and no problem. But if the hole for focuser squaring is off a bit then that's an issue. So I'll keep thinking about it.
What I may need to do is this:
1. Use the paper method to park the spot on my metal tube where the indexing hole goes.
2. Use a similar paper method to park the outside of the tube liner for both the center of the focuser hole AND the indexing hole. Then I'm not transferring anything from one tube wall to another.
I think it will work, just takes patience and extra time, but that's what it's all about with imaging
Quote:
Curt-
Even though the tube is powdercoated, you still could do that... easiest way to be certain the focuser is square. You could use a dremel hand grinder to grind a tiny spot instead of centerpunching it, to avoid any damage to the powdercoating- get enough of a dimple to start a hole... we're only talking a tiny hole.... but I do understand your reluctance. If it were me, I'd rather be certain my focuser was square, especially for astrophotography work.
Wes
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Curt
8" F5 Newtonian Astrograph
Orion 80ED CUSTOM
Edmund Optics 4.25" 'Palomar' Newtonian, 1968 vintage
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Wes James
Post Laureate
Reged: 04/12/06
Posts: 3459
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Curt-
Yes, you could do it that way- are you planning on pulling the liner back out after you mark the holed for the focuser and spider??? If so, what you could do- or something similar- is to simply stick the drill into the hole in the tube- and rotate it/drill it through/poke a hole through the liner- then when you bring it back out, just open up the hole with a razor knife to a 1/2" diameter hole or so- then you won't have to worry about the hole in the liner lining up exactly. Or, when everything's set up- and the liner's in- just stick the drill through, and you should still be able to shoot the laser through it- and see it outside the tube. Just a couple of ideas. You've got the right idea, though... I think it'd be worth the effort.
Wes
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Vic Menard
Post Laureate
Reged: 07/21/04
Posts: 3079
Loc: Bradenton, FL
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Quote:
...the Glatter laser...doesn't even have adjustment screws on it.
Really? My 2-/1.25-inch Glatter has alignment screws--although I've never had to use them!
Quote:
...I still don't understand why rotating the secondary wouldn't move the beam off the primary's center mark (assuming all other alignments are done).
Me either. Newtonian secondary mirror rotation and tilt are closely related (especially when the tilt adjustment is not confined to the plane defined by the OTA axis and the focuser axis). Secondary mirror rotation will indeed move the beam off the primary mirror center spot.
That said, the laser alignment you're discussing is simple axial alignment, aiming the laser at the primary mirror center spot is focuser axial alignment (even if you're adjusting the secondary mirror to aim the laser), and adjusting the primary mirror to aim the return beam at the laser emitter in the center of the focuser is primary mirror axial alignment.
Secondary mirror alignment involves aligning concentricities--in this case, the bottom edge of the focuser drawtube (or sight tube), the real edge of the secondary mirror, and the reflected edge of the primary mirror. Getting the axial alignment and secondary mirror alignment corrected simultaneously is what Newtonian collimation is all about.
Finally, you'll also need to select a reference axis to align to. Most Newtonian users choose the focuser axis, as it's the easiest, and it delivers excellent optical alignment. If you're looking for the ultimate mechanical precision, you may choose to go with the optical tube axis as the reference. Properly executed, using the OTA axis as the reference delivers precise mechanical alignment necessary for high-resolution DSC pointing accuracy.
Assuming you've built your astrograph to image, I would suggest you achieve the best possible mechanical alignment first, and then build a precision optical alignment on top of the mechanical alignment, giving special consideration to the focuser and primary mirror axial alignments--since they will ultimately define your image performance.
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 569
Loc: Riverview, FL, USA
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Vic,
What are your thoughts on adding diagonal offset to the mix, since optical alignment criticality is being discussed?
Mel
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Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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dawsonian2000
professor emeritus
Reged: 07/26/06
Posts: 569
Loc: Riverview, FL, USA
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Curt,
Either method would work. Wes' idea to create a dimple with a dremel tool would reduce extraneous damage to the powder coat finish. As for me though, I would go with the paper method. The paper can be moved, but the hole, well. 
Mel
--------------------
Clear Skies, Forever!
The Vega Sky Center
10" (254mm) F/5.65 Home Built Fork Mounted Newtonian Reflector
5" (127mm) F/9.4 Home Built Refractor (under construction)
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus Refractor
3.1" (80mm) F/6 Scopos ED APO Refractor
4.5" (114mm) F/8 Tasco 11te-5 Newtonian (under restoration)
2.4" (60mm) F/16.7 Tasco 7te-5 Refractor
2.4" (60mm) F/15 Jason Discoverer 313 Refractor
http://www.vega-sky-center.com
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