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magic612
Pooh-Bah
Reged: 09/30/08
Posts: 1035
Loc: Somewhere south of Chicago, IL
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So I'm now the (proud?) owner of a 127mm diameter, f/4.4 focal ratio lens. It's supposedly an achromat, and from the way it focuses during the day with my 32mm Plossl, I'd say it has decent color correction for such a fast lens. I bought it because I calculated that I ought to be able to make a very wide-field telescope with a 3 or perhaps up to 4 degree field of view. And, I got it for $40.
The gentleman whom I purchased it from indicated he got it as a surplus lens 40 some-odd years ago. It does look to have some purple anti-reflective coatings on it. He had it set up as a straight-through system, which even for a "young" guy like me (age 39), I think would be a bit hard on the neck. He said that the fixed eyepiece he had on it was an 18 or 25mm Erfle, but given it's rather narrow apparent FOV, it doesn't seem to be one. Anyway, the outer 25% of the field gets rather "soft" with that eyepiece; it looks much better across the field with my Plossl.
So I was planning on making a "cradle" for it so that I can use this scope on the tripod/mount I made earlier this year. I'm thinking of using some leftover 6" ID PVC pipe I have for the tube of the scope, setting it further back inside the pipe to make for a built-in dew shield. At the back of the scope, I thought I'd pick up one of these mirrors from Surplus Shed and angle the light cone up and out at a 90 degree angle (much better on the neck!). And given that I'm not likely to change eyepieces on it, I thought of using a "fixed" eyepiece (not sure what to use yet, but this eyepiece look interesting), with a simple plumbing hardware fine-focuser on it.
I'll likely flock the whole tube, and probably just put a very simple sighting system on it, given it's wide field.
Any other thoughts? Anything I should look out for on a lens this large/fast? Other ideas?
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- 10" Orion Dob, 127mm f/9 refractor, 127mm f/4.4 refractor, 5" f/8 Dob (homemade), 90mm f/10 Orion refractor, 114mm f/8 reflector, Tasco 11TE-5 reflector, 60mm Sears 6333-A refractor
- Orion Vista 10x50s, Sears #6207 7x35's, Jason Statesman 7x35's
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: 68
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Let me offer you my thoughts on this....
I recently received of one of Surplus Shed's 127mm, f/5.5 lenses, and I took a relative "minimalist" approach to building a rich-field scope from it.
I happened to do EXACTLY what you suggested with 6" ID PVC pipe. I've put the lens inside the pipe for both the "built-in dew shield" aspect as you mentioned AND because I thought this heavy achromat lens and its cell would be more safely mounted that way.
I attached a PVC reducer on the focuser end of the PVC pipe and am now figuring out the best way to get a standard Synta-type 2" focuser from another telescope mounted in it. I've JUST ABOUT gotten that part figured out, too.
After I've painted all the PVC and determined how I plan to mount the scope on my Orion Astro View EQ mount, I'll be ready to go! (I'll probably just use two screws to attach it through the holes in the mount's cradle. I drilled holes in the PVC main tube to set it up and test to insure the length I had cut it was appropriate. And why make it more complicated?)
I plan to use the set-up for binoscoping; I already have the binoviewers and several sets of matching eyepieces.)
I may add a flexible handle to the top of the finished OTA, since this thing is HEAVY!
Hope my experience helps! Good luck on the build...
Mike Lynch
Frankfort KY USA
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Mike Lynch
member
Reged: 04/07/06
Posts: 68
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Oh, yes.... One more point.
Look at the list of topics in this DIY forum for at least two other threads on how others have built a scope from this 127mm, f/5.5 lens. You'll see "127mm" or "Surplus Shed" in the name of the threads.
Some of these guys have taken their time and fashioned some great scopes from it!
Mike Lynch
Frankfort KY USA
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jog
member
Reged: 10/26/06
Posts: 94
Loc: nj
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can you post a picture of the scope?
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Mike Lynch
member
Reged: 04/07/06
Posts: 68
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Right now (LITERALLY!!) I'm in the process of spray-painting the PVC tube exteriors for this scope and an 80mm Short Tube I've made for a friend, using Surplus Shed's $39 lens.
I'll post some photos as I get close to completion... perhaps tomorrow(?)
Incidentally, for the orignal poster and other viewers, I have some adhesive flocking paper I bought from Scope Stuff for the interior of the 127mm scope. I've used it before, and really liked the results.
I've spray-painted the interior of the 80mm with flat black paint. This 80mm is essentially a little brother of the 127mm... put together in much the same way as the larger one with a PVC pipe and reducer for the focuser.
Mike Lynch
Frankfort KY USA
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magic612
Pooh-Bah
Reged: 09/30/08
Posts: 1035
Loc: Somewhere south of Chicago, IL
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Hey Mike - great stuff! Sounds like we do have similar ideas on how to mount something along these lines. I'll check out those other threads too (I think I perused one of them a couple weeks ago, now that I think about it). One thing I am doing a little differently is just directly mounting an eyepiece to an eyepiece holder with some screw threads directly above the mirror I'll be using. Because it's so short (22" focal length!), I didn't want to vignette the field, and this way I'll get full aperture. With that 38mm Surplus Shed eyepiece I mentioned in my first post, I'd have a 14x magnfication, and over a 4 degree field; with my 32mm Plossl, it's 17x and just over 3 degrees. Either way, it'll be a nice, rich field!
Jog - pictures of what I purchased are below. Of course, I'll be doing some significant modifications to make it work for my tripod/mount.
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- 10" Orion Dob, 127mm f/9 refractor, 127mm f/4.4 refractor, 5" f/8 Dob (homemade), 90mm f/10 Orion refractor, 114mm f/8 reflector, Tasco 11TE-5 reflector, 60mm Sears 6333-A refractor
- Orion Vista 10x50s, Sears #6207 7x35's, Jason Statesman 7x35's
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: 68
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David,
I can fully understand why you want to avoid vignetting the light path for your lens. And your web site shows that you are very into the DIY aspect of this great hobby.
Far be it from me (sincerely) to suggest there's a "better" way for you, but to be able to use as many eyepieces as you can with this scope, would you consider making a PVC focuser, too... as web page :
Perhaps a large enough PVC focuser tube, adapted at the eyepiece end to reduce to 1.25", would decrease the chances of the vignetting....?
Mike Lynch
Frankfort KY USA
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magic612
Pooh-Bah
Reged: 09/30/08
Posts: 1035
Loc: Somewhere south of Chicago, IL
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Hey Mike -
At the moment, I'm not sure I want to be able to use as many eyepieces as possible. My reasoning for getting this lens/scope was to make a very wide field refractor somewhere between my binoculars and other telescopes. Since I already have an ST-80, I can technically get an even larger field (if I wanted). But the largest field of view my scopes will generally produce (minus the ST-80) is about 1.6 to 1.8 degrees. So I'm looking for the maximum possible FOV with the best image possible. This really will be a "specialty" scope to hit that 3-4 degree field of view "sweet spot" but with more resolving power than my 80mm scope has.
The other thing I'll have to consider is balance. Because the mount I've already made for my f/9.4 scope is a bit narrower than what I'll be able to make for this one since I'll be using PVC pipe, I'm not sure I'll have the ability to do much in the way of balancing once the scope is together/set in the mount (unless I use counterweights, but I'd prefer to avoid that if possible). By having a "fixed" eyepiece, that will minimize balancing issues, as the weight on the eyepiece end won't change. Then the only focusing required would be minor changes depending on the person viewing.
Besides, with the mount the way it is, I can swap this scope in/out with my longer f/9.4 in about 10 seconds flat. So if I need higher magnification/more contrast/a narrower field for a given object, it's a simple swap - and both lenses are the same diameter.
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- 10" Orion Dob, 127mm f/9 refractor, 127mm f/4.4 refractor, 5" f/8 Dob (homemade), 90mm f/10 Orion refractor, 114mm f/8 reflector, Tasco 11TE-5 reflector, 60mm Sears 6333-A refractor
- Orion Vista 10x50s, Sears #6207 7x35's, Jason Statesman 7x35's
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
Pooh-Bah
Reged: 09/30/08
Posts: 1035
Loc: Somewhere south of Chicago, IL
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Okay, so I happened to be in the home improvement store today (how convenient that I had to buy housepaint!), and picked up a 1.25" to 1.5" PVC pipe adapter (these things are perfect for setting a 1.25" eyepiece into), a 1.5" pipe coupling and a 2' length of 1.5" pipe. I just may have to experiment with making a low-profile Crayford focuser.
Way to go Mike - you got me thinking about adding a focuser, and now I'm going to wind up doing more work on this scope and make it even nicer!  
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- 10" Orion Dob, 127mm f/9 refractor, 127mm f/4.4 refractor, 5" f/8 Dob (homemade), 90mm f/10 Orion refractor, 114mm f/8 reflector, Tasco 11TE-5 reflector, 60mm Sears 6333-A refractor
- Orion Vista 10x50s, Sears #6207 7x35's, Jason Statesman 7x35's
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: 68
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Heh-heh... I've been known to wander into the "telescope" section of some home-improvement and hardward stores myself. Actually get some good help when I explain what I'm looking for, too!!
OK, I've attached a couple of photos of the near-complete 127mm f/5.5 sewer, UH, I MEAN PVC, scope!! 
One heavy sucker!! may need to find a ring system to hold it securely to the mount!
I need to do some other refining, but one thing I like about this "design" is that, since the main lens is slightly smaller than the ID of tube, I should be able to do some collimation, if it's very far off.
The tube is pretty short because this setup will be used for binoviewing. I hope to get some looks at our partly-cloudy sky tonight to see how this works!
Mike Lynch
Frankfort KY USA
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Mike Lynch
member
Reged: 04/07/06
Posts: 68
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OK, perhaps I can't attache more than one photo at a time! Here's another!
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Mike Lynch
member
Reged: 04/07/06
Posts: 68
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Took the 127mm scope out for a short while as dusk was falling, but mosquitoes chased me back in before very long. I got some good sharp terrestrial views and views of clouds in the reddened western sky after the Sun went down. I was happy with those views.
Turned to the southeast to view Jupiter as it was rising higher. Not a real sharp view. Probably need some tweaking on the collimation. But, of course, this thing's going to do much better on deep-sky stuff (my favorite targets, 'specially planetary nebulae) than planets.
So far, so good. No major issues other than collimation and comfort that the heavy scope is securely attached to the mount! 
Mike Lynch
Frankfort KY USA
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magic612
Pooh-Bah
Reged: 09/30/08
Posts: 1035
Loc: Somewhere south of Chicago, IL
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Mike - looks good! You sure it's not vignetting the edge of the field though?
I took mine out (well, in the condition I bought it, see photos above) and placed it against my present mount to steady it so I could take it for a "test drive." Considering that the edges of the field looked soft during the day with the current eyepiece, I was pleasantly surprised at the nice focus it achieved at night. I'm definitely looking forward to adding a focuser and using my 32mm Plossl now. In between doing some more house painting, I'll hopefully get some work done on a Crayford focuser for it. I've drawn my proposed idea in AutoCAD of what I'd like to make (see attached PDF file); any feedback on that would be most welcome.
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- 10" Orion Dob, 127mm f/9 refractor, 127mm f/4.4 refractor, 5" f/8 Dob (homemade), 90mm f/10 Orion refractor, 114mm f/8 reflector, Tasco 11TE-5 reflector, 60mm Sears 6333-A refractor
- Orion Vista 10x50s, Sears #6207 7x35's, Jason Statesman 7x35's
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
Edited by magic612 (09/08/09 09:35 AM)
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Mike Lynch
member
Reged: 04/07/06
Posts: 68
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Good luck on your build....especially if you have to attend to those pesky little chores like housepainting!!
Are those baffles in your drawing? I've flocked the entire interior of my tube, but I wondered if baffles would make a difference.
While I dont' THINK it's cutting off the edge of the light cone, I need to take the time to simply draw a ray-trace diagram to see how it "calculates" out.
Dumb question (maybe): If you can see the inside edges of the lens cell while looking through the mirror diagonal without an eyepiece, is that any quick indication about such vignetting?
Mike Lynch
Frankfort KY USA
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magic612
Pooh-Bah
Reged: 09/30/08
Posts: 1035
Loc: Somewhere south of Chicago, IL
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Mike - yes, baffles in the drawing. I honestly haven't fully decided whether to include them or not, but I figured I should draw some in case I do incorporate them. I was going to go the 100% flocking method too, but decided that baffles wouldn't hurt, either.
I not entirely sure of the answer to your questions, but I suspect that you'd need to see the inside edge of the lens cell that are *inside* of the lens itself (in other words, the portion of the cell that is closer to the diagonal). Your lens is set a ways back into the cell, so it's possible you're seeing that "forward" portion of it. Without doing a ray-trace, I'd think you'd need to place a circle the size of the smallest field stop of the eyepieces you plan to use for the scope, and set it approximately where that field stop would sit when the eyepiece is in.
THEN when you look into the mirror diagonal, if you can see the back portion of the lens, that might (and I emphasize, *might*) mean you're getting full aperture. But those who are smarter about this stuff would answer that better - I'm honestly giving you my best guess! That's also why I drew mine out, so I could ensure I'd be getting full aperture.
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- 10" Orion Dob, 127mm f/9 refractor, 127mm f/4.4 refractor, 5" f/8 Dob (homemade), 90mm f/10 Orion refractor, 114mm f/8 reflector, Tasco 11TE-5 reflector, 60mm Sears 6333-A refractor
- Orion Vista 10x50s, Sears #6207 7x35's, Jason Statesman 7x35's
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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Michael Miles
professor emeritus
Reged: 02/11/05
Posts: 677
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Hi Mike:
I've' got one of these lenses too. Since you've got the lens cell mounted backwards, did you remove and reverse the lens assembly?
Michael
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LXD-75 w/
Stellarvue 102ED
Hardin 10" Newt
Antares 8" Newt
Meade AR-5
Meade N-6
Celestron 102mm refractor
Canon 300D, Meade DSI guiding
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StarStuff1
Pooh-Bah
Reged: 04/01/07
Posts: 1135
Loc: South of the Mason-Dixon Line
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An easy way to check for vignetting is to measure the exit pupil using an eyepiece of known focal length.
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Tools that make objects very far away appear much closer than they actually are.
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Mike Lynch
member
Reged: 04/07/06
Posts: 68
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Michael,
YES, I did do exactly that! But thanks for asking!
Since the cell fit more securely deeper inside the PVC pipe, and I wanted the dew- and glare-shield advantages of that setup, I carefully unscrewed the retaining ring, flipped the lenses together and re-attached the ring.
Have you built a scope with the lens? If so, what's the distance between the back edge of the lens and your focuser? (I realize you may have some posts on the "127mm Surplus Shed" threads here; I just haven't noticed all the names.)
Mike Lynch
Frankfort KY USA
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GlennLeDrew
Carpal Tunnel
Reged: 06/18/08
Posts: 1678
Loc: Ottawa, Ontario, Canada
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For visual work, if you can get full illumination on-axis only, that's generally good enough. As long as the offending 'baffle', such as inner opening of focuser drawtube, etc., is more than about three field stop diameters in front of the field stop, illumination fall-off will usually be so gradual that you'll never be able to detect it.
Moreover, some light fall-off in fast 'scopes is actually a *good* thing, as this means some off-axis light passing through the edge of the ojective is being masked, and this does slightly improve edge-of-field sharpness.
To determine if the inner end of the drawtube is acting as an aperture stop (i.e., reducing the effective aperture for on-axis imagery), measure the distance from that opening to the eyepiece's field stop. If it's less than the drawtube I.D. times the objective's f/ratio, you're suffering a reduction in aperture.
For example, say the focuser tube's I.D. is 2" and your objective is f/5.5. The maximum allowable separation between eyepiece field stop and inner end of the drawtube is 2" x 5.5 = 11".
But it's easy to just look and see, *if* you can place your eye where the eyepiece field stop will lie (that is, at the focal surface.) You'll likely have to remove any diagonal, and then focus on a distant subject using a magnifier and rack the focuser until the drawtube's outer opening is *also in focus* with the image. Center your eye, and look for the actual edge of the entire objective to be visible without having to move your eye off-axis. As long as this condition is observed, you're fine.
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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 (mostly DIY stuff)
Simple minds discuss people. Good minds discuss events. Great minds discuss ideas. - Hyman Rickover
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Mike Lynch
member
Reged: 04/07/06
Posts: 68
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Thanks to ALL of you for your thoughts. I had a busy evening, and I won't have a lot of time to complete the measurements for a couple of days, but suffice it to says that it DOES look like I'm vignetting the light path from the lens in my 127mm scope, at least when it's racked in for some eyepieces, based on a ray trace drawing I've done. (That's obviously not a surprise to some of you!!  )
I need to carefully measure the location of my focuser tube end at its most racked-in position for my eyepieces and determine what's going on.
I THINK I can reduce the length of the tube, if that, in fact, can remove the "offending" length of it. Guess we'll see.
Mike Lynch
Frankfort KY USA
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