Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Ron, it's not THAT narrow. With the 24.5 Meade Super Wide, the moon is just slightly larger than my field of view. (4810mm / 24.5mm equals ?)
And I have a Paul Rini 0.5X reducer nearby. Only problem with that is that it shifts the image plane enough so I must remove the diagonal to use it.
When I build a special diagonal with a three degree tilt, I can then use a ccd camera and capture all those lovely images.
Or, I can really shoot them through my 12.5" F/8 and lie about them!
Why isn't THAT scope shown here? Because I didn't realy build it. I was given the scope and restored it after it was abandoned for years in a basement of a college that couldn't deal with it because it was too big. If I ever refigure the mirror to better numbers, then I may post it as mine but not until then. It's now a 1/12 so don't hold your breath!
There are pics of it elsewhere here at CN. You've seen them I'm sure.
Art
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Keith, Bill Cheng kids me a lot and I can't resist an opportunity to tease him back a little. Talented guy really, even if he can't do a hammerhead in a taildragger.
As evidenced by the fact that he took second in optics at Stellafane this year!
The mirrors in the Schief are the first mirrors I have ever made and finished! Granted, I had coaching from Gordon Waite and Dave Groski personally (Bill Cheng too!)but the pushing of the glass was mostly my doing. It's two spherical mirrors. that's all.
The use of an optical flat does not save much. You already have the secondary mirror in the convex tool you ground the primary with! You just need to match RC and F/L. No big deal.
Art
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Ron the filters are placed between the two relay lenses and mounted in such a way that they can be tilted. I chose a two axis gimbal mount for each filter with threaded rods going back to "collimation" knobs near the focuser.
Here is the schematic that Dave shows at his web site. There is quite a bit of lattitude in the lenses.
Anything beyond this, please, lets start a new string.
Thanks
Art
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Rob asked: "Art, that looks like an unabstructed Schiefspiegler".
It is!
Rob wrote: "Actually the primary looks as if it is mounted laterally, apposed to underneath the secondaary tube assembly."
That's simply the result of camera angle, lighting and perhaps the head was tilted. You can mount it anyway you want realy. I think Dave has his mounted horizontally. I know Bill Chengs 4.25" is mounted horizontally too
Ron asked "Interesting. Do you own this scope now?"
You betcha! I'll be replacing the all aluminum cradle with a composite one to save weight.
That's it in this, here at this string Ron. If you want more details, please comtact me off line or lets start another string please.
Thanks
Art
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Rob"
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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Brian Carter
Post Laureate
Reged: 11/24/04
Posts: 3115
Loc: Atlanta, GA
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Here's mine, with the shrowd it admittedly looks better.
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10" F/5.5 Astrosky
SkyCommander DSCs
A loving dog, Buddha, who tolerates my hobbies
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Thanks for the kind words but Rob, I hate math! I avoid anything higher than trig or geometry whenever possible!
With the engineering software I use, I don't even need to do that! Contouring the top and bottom of the replacement mount was actually quite simple.
I simply copied the contour of the secondary tube and cut the block to match. Ditto with the primary cutout below.
Those are the only critical cuts as they determine the intercept angle of the two cells.
Anything else is merely artistic license with the only limitation being sure that there is sufficient material to support the loads.
The core is made from low density expanded foam, shaped just as you saw and then draped with impregnated fiberglass, vacuumed and allowed to cure.
Art
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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dawsonian2000
member
Reged: 07/26/06
Posts: 78
Loc: Riverview, FL, USA
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Hello Art,
It is good to find you here under the "Post a picture of the scope you made" forum. Your collection of home-built telescope instrument are impressive in the least!  Though I am very fascinated with the collection (especially the Schiefs) you have constructed, my desire is to build a 60mm Solar H-Alpha telescope some time in the future. I was hoping I could lean upon your compassion, understanding, and knowledge base in this area when the time arrives.  In the meantime, I am still working on the OTA for my 10" Fork Mounted Newtonian. I resently finished painting the tube and now I am giving it ample time for the paint to cure. I truly look forward to posting a picture of my completed reflector in the future.
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Clear Skies, Forever!
Mel Dawson
The Vega Sky Center
10" (250mm) F/5.65 Fork Mounted Newtonian Reflector
3.5" (90mm) F/11.1 "Vixen-Spec Modified" Konus GEM Refractor
3.1" (80mm) F/6 Super ED APO Triplet Refractor
4.5" (114mm) F/8 Cosmos (Grampus) GEM Newtonian
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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Stefan Rostyne
scholastic sledgehammer
Reged: 10/19/04
Posts: 943
Loc: Assenede, Belgium
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Wondefull instruments in this thread!
This is one of latest homemade toys : 4.5" f/4.5 fully baffled widefield
I am currently constructing the hardware for a 8" f/5.5 traveldob. All must fit in a 12" cube. Once that finished, I start rebuilding my 12.5" f/5. It is now in a fully baffled tube like the one above, but I'll reconfig it into an ultralight truss.
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Stefan Van de Rostijne
4.5" F4.5 newt 5°widefield/finderscope
8" f/5.6 travel dob
old 12.5" F5 dob (used to look better...)
30 cm f/30 Classic Cassegrain (polishing primary)
23" f/4 dob project
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6190
Loc: Bremerton Washington
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Quote:
Hi,
...the only scope I ever made, yet. My f5 80mm surplus shed refractor for camping trips - it weighs less than 2kg. It has a PVC tube, wooden DIY rings and I recently finished my MK3 Crayford from salvaged anodised 6mm aluminium - all constructed with handtools (a bit of a struggle but it works). The objective is surprisingly good for $30. Its my attempt to join the travelscope revolution!
Theo
http://homepage.ntlworld.com/t.allnutt/campscope2.jpg
Theo,
Great job!
Even what we call the simplest is still fun to see.
I like your focuser....
Rob 
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6190
Loc: Bremerton Washington
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Quote:
Hi Mark!
Without having seen the Brachyt, I am not in a position to make any comparisons.
Having said that there are several things you should know.
First, David Groski has this uncanny nack for "Making a Silk Purse out of a Sow's ear".
I tend to complicate matters. I go for exotic solutions; Dave is forever coaching me on the KISS principle. He keeps thim simple and affordable far better than I.
Both his 4.25" and 6" Schief share this design intent in common and make fabrication simple. So simple in fact, that I know an airline pilot who built one! 
Both of Dave's design use spherical mirrors. No need to go through the "parabolizing crazies".
The tool for making the primary is polished until it's within 0.5% of the RC of the primary. It's then polished some more using a simple interference test done with a home made light source until it matches the F/L of the primary. Then it's trepanned to the smaller diameter secondary size, using a drill press, a hole saw and some mirror grit.
There was no existing structural geometry, just the light paths and ray tracings for the optics. That meant I had to start from scratch. (I wonder how that airline pilot managed? They don't fly planes, they just push buttons!)
In any case, it is a simple design to construct (ask the airline pilot!). If you choose to go with the six inch variant, the only precuation I might make to insure good results is to make a one piece tube from rocket airframes from the folks at Public Missiles, and wrap it with a layer or two of light weight Bidirectional fiberglass. If you use a fork mount, this caveat can be ignoredas the scope will always be in essentially the same attitude.
However, with a fork mount, inevitably you will get to that DSO or planet whose position means flipping the scope "over the top".
If the secodnary tube lacks the mechancial stiffness, it will flex in the other direction and "poof!" there goes your collimation.
This is not a problem in the optical design but a failure on my part to anticipate the loads such movements generate in an optical system and either design it and/or build it properly.
You MUST have a good finder scope and it must be "zeroed in" with the main system or the scope is practically of no use except on the moon, which for some people is fine.
Remember that with a 4810mm focal length, even a super wide field eyepiece like a Meade 24.5 (my favorite) generates a magnification of close to 200 X!
Longer eyepieces (40mm and up) will help some finding things but if you don't have the finder scope in good working order, you'll invent cuss words.
It's a remarkable telescope with clarity and contrast that blows peoples minds and, it does it with garbage eyepieces!
I would not swap it for anything else as a highly effective portable planetary scope. That it's inexpensive to build adds to it's value.
Here is a shot of a 4.25 inch Schief built by Bill Cheng who just happoens to be an airline pilot. Somehow, he managed to build this thing. Last time I looked, he still had ten fingers.
Art
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That is awesome!!!!
Rob(and to think, when I mentioned schiefs in my suggested scope list at the beginning of this thread, who woulda guesses I'd see one/two?) 
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6190
Loc: Bremerton Washington
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Quote:
Here's mine, without the shroud, which admittedly makes it look better :-(
Beautiful scope Brian, great job..
Rob
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6190
Loc: Bremerton Washington
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Quote:
Thanks for the kind words but Rob, I hate math! I avoid anything higher than trig or geometry whenever possible!
With the engineering software I use, I don't even need to do that! Contouring the top and bottom of the replacement mount was actually quite simple.
I simply copied the contour of the secondary tube and cut the block to match. Ditto with the primary cutout below.
Those are the only critical cuts as they determine the intercept angle of the two cells.
Anything else is merely artistic license with the only limitation being sure that there is sufficient material to support the loads.
The core is made from low density expanded foam, shaped just as you saw and then draped with impregnated fiberglass, vacuumed and allowed to cure.
Art
====================
Fantastic!
Is it possible to purchase the primary, and secondary mirrors?
Rob(I put a bad effort at pushing glass, and it aint my favorite thing to do)
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6190
Loc: Bremerton Washington
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Quote:
Thanks for the kind words but Rob, I hate math! I avoid anything higher than trig or geometry whenever possible!
With the engineering software I use, I don't even need to do that! Contouring the top and bottom of the replacement mount was actually quite simple.
I simply copied the contour of the secondary tube and cut the block to match. Ditto with the primary cutout below.
Those are the only critical cuts as they determine the intercept angle of the two cells.
Anything else is merely artistic license with the only limitation being sure that there is sufficient material to support the loads.
The core is made from low density expanded foam, shaped just as you saw and then draped with impregnated fiberglass, vacuumed and allowed to cure.
Art
====================
After thinking about it, I realized that you are making that mount from foam, and then covering it to reduce on weight, and to firm it up... Is this correct?
I thought of using a Balsa core then laminating with fiberglass. I have seen fork mounted schiefs, but to mount one on a GEM is exciting......
I'd like more info on this design, and your fabricational methods.... 
Rob(and to think I thought no one made these exotic scopes any more)  What was I thinking
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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rnabholz
scholastic sledgehammer
Reged: 07/25/04
Posts: 765
Loc: Iowa
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With a hat tip to Ron R, here is my two strut 13.1".
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Rod Nabholz
Home Built Astronomy Projects
Wild Bird Photography
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6190
Loc: Bremerton Washington
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Quote:
With a hat tip to Ron R, here is my two strut 13.1".
I have not seen to many 2 strut dobs lateley.
In your assessment, are they stable?
From the shear mechanics, they sure look easier to build.
Great looking scope rnabholz..
Beautiful.
Rob
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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I purchased two blanks from Newport. The Sagitta is so shallow I felt it pointless to order them preground.
However, a bunch of people chose to make 4.25" Schiefs at the last Delmarva Mirror Making event and Newport was able to provide accurately preground blanks.
That being the case, I would encourage you to buy them from Newport with both the mirror and the tool pre-ground. I would also suggest that you spend a few extra bucks getting the back of the tool polished as well.
The reason for this is that you will be doing an interference test and need to be able to see through the top of the tool to evaluate the defraction lines generated when it is in direct contact with it's mate, the Primary.
This sounds a lot more difficult than it really is. You are using the same pitch lap and techniques as you would any other mirror. And, the same TOT, MOT positions and strokes.
As for purchasing them already figured and coated, I doubt it. There simply isn't enough money to be made with small aperture mirrors and not enough demand to entice mirror makers to take this on.
Here's what an interference test looks like in process. It's similar in some respects to using a Ronchi grid but the interference generates the grid lines. Typically they start out as concentric circular rings with their origin somewhere outside the mirrors.
As you polish and match the curve of one to the other, the lines start to straighten out. Eventually when you get to what yous ee in the picture, you stop. Unless of course an airline pilot tells you to stop. That's when you keep going. What do they know?!
Art
=========================
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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Art Bianconi
Post Laureate
Reged: 03/06/06
Posts: 4659
Loc: Delaware River Valley, New Jer...
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Ultralight Trusses are a real challenge! In a Dob you can monkey with the bearing size or depth to get access to the center of gravity.
But. . . . . .
if it's a fork mount or a split ring, the leveraging ratio on both sides of the CG will be very sensitive to even the slightest weight difference in eyepieces.
I gave up. Although I hate doing so, I had to go to a full thickness mirror, added a battery and still had to add about 4 pounds of lead to make things work.
If you discover secret to this nightmare, please let me know!
Thanks
Art
======================
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“Everything is on its way to somewhere. . . . . everything!"
____________________ George Malley (John Travolta)
________________________ "Phenomenon"
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theoUK
sage
Reged: 04/22/04
Posts: 234
Loc: N. Yorks, UK
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Hi,
here's the close-ups of the Crayford and a partial schematic. Its held together with machine screws (only larger holes are tapped). All the parts were salvaged from various old electrical items. The bearings and steel rod were from an photocopier - they are full of them!
http://homepage.ntlworld.com/t.allnutt/Cray1.jpg
http://homepage.ntlworld.com/t.allnutt/Cray2.jpg
http://homepage.ntlworld.com/t.allnutt/Cray3.jpg
http://homepage.ntlworld.com/t.allnutt/focuser.jpg
Theo
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Vixen SP
TAL-150P
Surplus shed f5 travel scope
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 6190
Loc: Bremerton Washington
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What is the medium you use to engage the focuser?
I see it aint rack-n-pinion.
Is it friction?
Also, are your bearings on lateral slides to adjust contact tention?
Rob(me want's to know)
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www.goldmtobservingcenter.com
Providing a great place for amateur astronomers, and ATM's to come and enjoy their hobby.
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rnabholz
scholastic sledgehammer
Reged: 07/25/04
Posts: 765
Loc: Iowa
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In my experience, the two strut is very stable.
The poles are quite stout - 2" diameter and .065 wall thickness, that helps a great deal. The nature of the clamps helps some too.
I get a small movement of the laser collimator's dot as I move through range of altitude motion - maybe an eighth of an inch, nothing of concern and nothing that causes any noticeable image issues.
As to ease of construction, it does simplify things a great deal. Simple focuser board instead of a cage and simple clamping mechanism are the main advantages.
Thanks for the interest
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Rod Nabholz
Home Built Astronomy Projects
Wild Bird Photography
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