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Mike Lynch
member
Reged: 04/07/06
Posts: 52
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Well, after staying up late to get some yard work and required reading done, I came downstairs to take a look at my 127mm setup and determine what needs to be done about the focuser vignetting the light path. The answer appears to be elegant, simple, and one I didn't want: Flip the lens cell around (and, of course, flip the lenses themselves, too!) and attach the cell to the tube in reverse direction.
My ray-trace diagram indicates the focus-tube end will likely be far less of a problem and may need no shortening at all, since the lens will be significantly further away.
I'll determine for sure after I drill some holes in the bottom lip of the cell and securely re-attach it to the tube. I can determine if all my eyepieces can come to focus with this arrangement.
My hope to use binoviewers without an OCA, however, may have just evaporated! Guess we'll see!
So "Thanks!" again to those who asked that important question about vignetting. I think I have a better appreciation of why David's considering a fixed diagonal mirror and a permanent eyepiece! Avoids the focuser-tube vignetting possibility altogether!
Mike Lynch
Frankfort KY USA
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magic612
professor emeritus
Reged: 09/30/08
Posts: 559
Loc: Somewhere south of Chicago, IL
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Hey Mike - It's all about maximizing light-gathering capacity; good to hear that it sounds like you'll be getting full (or close to full) aperture. Hopefully the binoviewer will work too, and still come into focus.
Although I'm still going with the "fixed diagnonal" idea, I'm working on designing a low-profile Crayford focuser that has a large enough draw tube so the vignetting won't be an issue. It'll just take some "back and forth" with the main lens to determine the best spot to place it for optimal focusing.
Ah... well, I can get to that after the outside painting of the house and inside painting of the bathroom is done. Gotta love "vacations"....  
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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Mike Lynch
member
Reged: 04/07/06
Posts: 52
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Heh-heh! I agree: Maximizing the light. When I get the new "flipped" set up finished, I may realize how much light I was MISSING with most of my eyepieces!!
Mike Lynch
Frankfort KY USA
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Mike Lynch
member
Reged: 04/07/06
Posts: 52
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Now, why didn't some of you people knock me in the head (gently, I would have hoped!) and tell me what was wrong with my thinking?! 
I'm back in business now with the 127mm f/5.5 refractor, and it finally dawned on me that my problem was that I wanted to use my binoviewers only, and didn't consider where the focus was going to be for cyclops viewing OR how much vignetting would occur for the binos. The focus tube was going to have to be in a particular location for each, no matter what! DUH! (Go ahead! Have a good laugh. It's my birthday weekend, and everyone should be partying and laughing!)
The photo shows my re-configuration. Lens cell pushed outside the PVC tube, and focuser in a position for cyclops AND bionoviewer use (but only with my Burgess 1.9x OCA.). The focuser tube is at or just outside the vignetting point for cyclops mode and just inside it for binoviewing. I'll probably carefully cut off the inside inch or so... or I could look for a shorter focuser.
Clouds and rain in the forecast for a couple of days... of course.
Mike Lynch
Frankfort KY USA
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magic612
professor emeritus
Reged: 09/30/08
Posts: 559
Loc: Somewhere south of Chicago, IL
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Okay, well after a long while of hemming and hawing over what direction I was going to take with the Crayford focuser I planned to make for this scope (read: procrastinating), I finally designed the focuser tonight. I'm satisfied with how it looks in CAD. I expect it should work fine, although the proof is always after it's built. I hope to get to that later this week, depending on kids' schedules after work.
I'm going for a very simple wooden Crayford, since I don't have much in the way of metal working equipment. But something along these lines seems practical and perfectly workable. So that's the direction I'm headed, with a few minor tweaks (adding ball bearings to the shaft, using PTFE tape for the pads).
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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magic612
professor emeritus
Reged: 09/30/08
Posts: 559
Loc: Somewhere south of Chicago, IL
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Oops, almost forgot: I did cut and paint a section of PVC pipe for the new tube, but I'm not terribly happy with how it looks. But since the weather has cooled off significantly since then, I may have to put off a fresh coat of paint until sometime in the spring, unless we get a warm spell here pretty soon.
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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gatorengineer
scholastic sledgehammer
Reged: 02/28/05
Posts: 882
Loc: Hellertown, PA
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Hey Mike,
Look at Siebert Optics for a zero Mag OCA.... Other suggestion is to try a prism diagonal, the light path is shorter than a mirror..........
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20" F5 Dob
16" Dob in pieces
Comet Catcher
MN71
12" Doc Clay Sky Patrol MEADE SCT
12.5" F4 Newt under construction
Siebert 45mm Binoviewers
Lots of binos---
Optics Past - 8" Stf Mak, 4" B&W triplet, 6"Schmidt newt, 12"LX200, C8, Meade LX10-10", 10" MEADE ACF, SN8, TAL150K, Orion 150MC, Jason 60mm refractor, ATM 6" F8, WO 110FLT, 92mm Off Axis Newt, Televue Genesis, Nikon 20x120 bino's, 15x110 Boarderguards, Kuhne Flaks
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Mike Lynch
member
Reged: 04/07/06
Posts: 52
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Interesting you should mention the Siebert OCA. I just picked on up on AstroMart; it's the 1.25x version, and it DOES work well! The increase in magnification is not objectionable, and the focus tube remains completely out of the light cone! 
Mike Lynch
Frankfort KY USA
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magic612
professor emeritus
Reged: 09/30/08
Posts: 559
Loc: Somewhere south of Chicago, IL
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Some progress today - I got the Crayford focuser made. It took longer than I'd hoped, but it looks nice too, and works surprisingly well considering it's a wooden one using PTFE (Teflon) tape for the bearing surfaces. Needs some paint and a more appropriate bolt for the tension, but other than that, it's good to go.
Mounting the lens in the tube looks like it might be easier than I initially anticipated, but I don't want to get too overconfident until I actually do it. But a few tests with some basswood strips gave me reason to smile. So hopefully I'll have time for that later this week. Then I'll need to build a rear cell that will hold the adjustments for the internal diagonal mirror.
More to come soon... 
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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magic612
professor emeritus
Reged: 09/30/08
Posts: 559
Loc: Somewhere south of Chicago, IL
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Well, the weather finally warmed up a bit, so I managed to get the interior of the PVC pipe painted all flat black (though eventually it will get flocked), and the outside gloss black. Here's a couple pictures of the simple wooden Crayford focuser on the pipe section. The "bearings" are simply some PTFE tape on the wooden blocks, and I plan on changing the tensioning screw to a thumbscrew instead of the "washered" bolt.
Also, I should note that the PVC 1.25" pipe adapter works very nicely as a receptacle for 1.25" eyepieces - it's a simple compression fittings, so just pop the eyepiece in, turn the fitting, and it's tight/centered! All I did was place it into a simple coupling, which serves as the focuser tube. Just a bit of cleaning up of some minimal flash, and it's quite smooth all the way through it's motion. Oh, and I used some silicone tubing to give some "cushioning" between the carbon fiber rod and the PVC coupling. At the moment, some extra silicone tubing is holding the flanged ball bearings in place; I'll likely update those to something that will stay in place more permanently.
I'm pretty excited; can't wait to get this finished and try it out!
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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GlennLeDrew
Pooh-Bah
Reged: 06/18/08
Posts: 1283
Loc: Ottawa, Ontario, Canada
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Nice job on that focuser!
How will the diagonal be supported?
If space and layout considerations permit, how about orienting the focuser so that the roller shaft is on the objective side? (Assuming your pics represent the back end of the 'scope's tube.) To me, it seems preferable to have less 'stuff' under one's nose and cheeks.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces
My Gallery
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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magic612
professor emeritus
Reged: 09/30/08
Posts: 559
Loc: Somewhere south of Chicago, IL
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Thanks Glenn!
I plan on supporting the diagonal from the tube cap that I'll have to make. It will essentially be like a reflector's secondary, except instead of having spider vanes to support it, I'll be able to use a solid piece of wood. Then I'll have collimation bolts in the back, to adjust the diagonal mirror.
Good point about orienting the focuser the other way - the tube hasn't been cut yet, so I can still manage that. I'll have to revisit the CAD drawing and double check how my diagonal support structure is set up, and if I have the room, I'll probably change that. (In the pictures above, the focuser is simply set on the tube for the photos sake.)
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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magic612
professor emeritus
Reged: 09/30/08
Posts: 559
Loc: Somewhere south of Chicago, IL
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Well, I made a lot of progress on this the last few days:
- Focuser finished (and slightly upgraded)
- Tube cap with mirror completed
- Tube mount cut and assembled
- Lens cell installed properly
So, it was successful in the sense that "it worked." The focuser worked quite nicely (more on that later though). I was rather amazed at how many stars I could see with it! And - I was quite impressed with the lens overall - with my 32mm Plossl, stars were visible and seemed point-like out to the edge of the field - not bad for an f/4.4 refractor.
That said, there were some issues I need to fix. One, I merely "eyeballed" the secondary mirror, and given that bright stars displayed a "flared side" which seems to be caused from the slight mis-alignment of the secondary. But I didn't fix that yet because....
The tube mount hits the cradle I built specifically for my other 127mm scope (the f/9.4). So although I was able to "hand hold" the tube in place and view a few things that way, I could in no way shape or form use the scope as intended. It's my own fault, of course - I thought, "Hey, I'll just build it to the width of the other scope mount and it will work" - failing to account for the brace on the back of the cradle. It's not a difficult fix - I just need to reposition a wood brace - but it was enough to warrant a big:
So I couldn't collimate the secondary while hand-holding the back of the tube too. I'll get there, though.
The other minor issue was the PVC coupling I used for the focuser tube has a VERY slight angle to the outside surface. So when it moves slightly past the halfway point, it barely - but perceptibly - shifts. However, since I managed to place the focus at a point where the focuser need not move much, I think I've managed to avoid the need to have the focuser move past that point at all. It stays in a "non-shifting range" so to speak. My raytrace also showed that I'm presently not vignetting at all, but if I went to the 1.5" pipe, I would. So I think the minor problem is really not one at all. It simply required very careful lens-cell placement.
Overall, everything else worked well, and with a few minor tweaks, it ought to be in good shape. Like I said, I was VERY impressed with the views - an unobstructed 127mm view, even from light-polluted skies, was really amazing. LOTS of faint stars were visible, and I think with the secondary collimation and a smoothly moving mount, I'll have quite the nice scope.
It's not all that heavy, so although it's not quite "grab and go" (due to the large tripod I'll be mounting it on) it will still be very easy to transport and move. And the detail it showed now - uncollimated - gives me great hope for what I'll be able to see later when it's really tuned up! 
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- Celestron C8+, Orion 90mm f/10, Orion ST-80, 5" f/8 Dob, 127mm f/9.4 refractor, 114mm f/8 on DS GoTo, 60mm Sears 6333-A, 127mm f4.4 refractor lens (current project), 12" f/5 mirror (future project)
- Orion Vista 10x50s (5 deg), Sears #6207 7x35 (7 deg), Jason #138 Statesman 7x35 (11.5 deg)
Yes, I'm addicted to telescopes and binoculars. I am getting help. Every time I look at the heavens, it helps.
http://www.eyesonthesky.com
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