Jerry Hyman
super member
Reged: 03/29/07
Posts: 120
Loc: Mesa, Arizona
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I am looking at possibly building an 8" f6 Newt with a Royce Conical mirror, and then mounting it on the new iOptron Mini-Tower alt/az goto mount. It will most likly be using the Protostar solid resin tube.
I would appreciate it if you can tell me where approximately the balance point would be on this OTA.
Thanks in advance!
~jerry
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9.25" Celestron carbon fiber SCT
Vixen Super Polaris Deluxe mount
Vixen Super Polaris mount
Burgess BV24 Binos
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Sean Cunneen
professor emeritus
Reged: 08/01/07
Posts: 565
Loc: Blue Island Illinois
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All of mine balance between a quarter and a third of the way from the mirror side. I have to weight the front of my scopes as I get less vibration if they are mounted close to the center of the tube. For you, it mightbe different. Every scope is different. In order for someone to answer that question for you, you would have to weigh every single component and measure how far from center each item is. By the time you finished doing that, we'd all be too old to punch the buttons on our extra large calculators!
It's much easier to build it and measure your center-of-gravity directly. Can I ask why you need the info?
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Sean Cunneen
Blue Island IL
8" f/8 Home built Newt, Discovery mirror, curved vane spider, CG5 Motorized head with Intelliscope DSC, Pier
C102hd CG-4
100mm F4 Cedar Tube RF Refractor
2,3,4,5,6mm Televue Plossls
27T3,33T3,44T3
9-22 Ethos Zoom
NO, I'M NOT SELLING!
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perfessor
sage
Reged: 12/30/07
Posts: 321
Loc: Northern Illinois
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What Sean said.
Build the scope first. After all, you know where the primary goes; you know where the secondary goes; you know where the focuser goes; you know (roughly) where you want the finder to go. Go ahead and put them there.
Put an eyepiece in the focuser. You can heft the OTA by hand and probably get the balance point within an inch or two. Roll it on a dowel to get closer. That's where you mount the bearings.
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Tom
"Don't always know what I'm talkin about"
8" f/7
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Jerry Hyman
super member
Reged: 03/29/07
Posts: 120
Loc: Mesa, Arizona
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Thanks Sean and Tom for the responses. I have never built a telescope before and I am looking forward to having that experience.
The reason I asked the question is that I have asked a vendor of the iOptron mini-tower if a 48" long 8" f/6 Newt would work on his mount, and his reply was that it depends on where the balance point is (so as to know if it will clear the tripod legs).
I do have a few other questions questions: I am trying to figure what size secondary to order, and when I use a free program called "Newt" I get two answers I need to understand better on 100% field illumination and 75% field illumination.
When I specify a 1.52" diagonal minor axis I get a 19% CO and 100% illumination of .1504" and 75% illumination of .9046". When I specify a 1.83 diagonal minor axis I get a 23% CO and 100% illumination of .5259 and 75% illumination of 1.254".
My original goal with this telescope is to have it for visual observation only with DSO's being the prime objective (galaxys, nebulae, open and globular clusters)and also capable of having decent, if not perfect, apo like views of the moon, planets, and double stars.
My 60 year old eyes are capable of only about 5.5mm pupil dialation and I want a minimum of a 1.8 degree to 2.00 degree TFOV which I should be able to get with a 31 Nagler or 28mm UWAN.
So my question is this: Will I get a better view with less notable vignetting with the 1.83 minor axis with it's greater 100% illumination but still have very good performance on planets with the 23% CO, or would the smaller 100% illumination of the 1.52 minor axis and it's smaller CO be better if the 75% minor axis not be noticable to the eye on large clusters and nebulae? I just don't have any really practical real life experience in this area to answer this question for myself.
Again thanks for your help on this!
~jerry
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9.25" Celestron carbon fiber SCT
Vixen Super Polaris Deluxe mount
Vixen Super Polaris mount
Burgess BV24 Binos
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Sean Cunneen
professor emeritus
Reged: 08/01/07
Posts: 565
Loc: Blue Island Illinois
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I don't have any experience with that mount directly, but I have LOADS of experience undermounting telescopes in general! I doubt the mount was designed to handle such a large tube, while you certainly could and get away with it, you run the risk of it tipping over. What the vendor was saying is that the tube when near vertical runs the risk of bumping into the tripod legs. The cure would be to move the tube farther out from the mount. With that style mount, you can counterbalance, but only 8#. The lightest I've ever built an 8" f/6 was 11# and that was pretty flimsy. So you run the risk of having your scope very tipsy on it's mount at some orientations. That Ioptron is a neat mount, but it is geared more for Rich-field refractors than large aperture, long tubes. You can find a Goto CG5 for a similar price and the GEM style mount LOVES to be loaded up!
As for your second question, if you use a 31 Nagler, you'll need every bit of illumination, so shoot for 100% don't lose sleep over the increased CO, you'll never miss it. What you won't have is vignetting which you'll see in wide-field eyepieces.
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Sean Cunneen
Blue Island IL
8" f/8 Home built Newt, Discovery mirror, curved vane spider, CG5 Motorized head with Intelliscope DSC, Pier
C102hd CG-4
100mm F4 Cedar Tube RF Refractor
2,3,4,5,6mm Televue Plossls
27T3,33T3,44T3
9-22 Ethos Zoom
NO, I'M NOT SELLING!
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Jerry Hyman
super member
Reged: 03/29/07
Posts: 120
Loc: Mesa, Arizona
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Thanks Sean!
~jerry
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9.25" Celestron carbon fiber SCT
Vixen Super Polaris Deluxe mount
Vixen Super Polaris mount
Burgess BV24 Binos
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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Hi Jerry,
Do you have a focuser and finder in mind?
Are you going to use the 10" diameter tube for the air space it provides?
What material were you going to use for the mirror cell and how thick?
Best Regards,
Roy
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Roy
MN65
114NT/500
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Jerry Hyman
super member
Reged: 03/29/07
Posts: 120
Loc: Mesa, Arizona
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Hey Roy, it is good to hear from you! I plan on using a moonlite focuser. Telrad for the finder. So far I am thinking about a 10" Protostar blacklite resin tube. I am not sure about the mirror cell or even if I need one if I go with a Royce conical mirror.
C.S.
~jerry
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9.25" Celestron carbon fiber SCT
Vixen Super Polaris Deluxe mount
Vixen Super Polaris mount
Burgess BV24 Binos
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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Thanks Jerry,
You'll need some sort of support for the bolt. How about birch ply for now.
Any fans?
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Roy
MN65
114NT/500
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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Also,
What are your mirror face to focuser hole, focuser to front end of tube, and mirror face to back of tube dimensions?
I assume you will use only a 48" tube?
Roy
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Roy
MN65
114NT/500
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Jerry Hyman
super member
Reged: 03/29/07
Posts: 120
Loc: Mesa, Arizona
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Focuser to front end of tube is 6". Mirror face to back of tube is 3.5". 39.625" for mirror face to focuser hole. I plan on two fans (one mounted at the bottom and another at the side of the tube near the mirror surface to upset the boundry layer). Planning on a 48" tube and birch ply to support the bolt sounds good for now.
~jerry
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9.25" Celestron carbon fiber SCT
Vixen Super Polaris Deluxe mount
Vixen Super Polaris mount
Burgess BV24 Binos
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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Here is what you have so far.
I still need to add the 3/8 nuts to the post for an accurate CM. Can't promise anything tomorrow night, but I should be able to continue on Wednesday.
Cheers,
Roy
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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Bottom view
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KerryR
sage
Reged: 12/05/07
Posts: 327
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Here's another diagonal calculator. I think it's a little easier to use than Newt.
http://www.opticwavelabs.com/education.html
According to Kreige and Barry, .5" fully illuminated field is more than adequate on an 8" scope. They say the drop-off outside that field, while present, is inconsequential.
Kerry
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Kerry
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Sean Cunneen
professor emeritus
Reged: 08/01/07
Posts: 565
Loc: Blue Island Illinois
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I have to weight the front of my scopes as I get less vibration if they are mounted close to the center of the tube.
Sorry, I wanted to type that again because it's very important for a vibrationless setup!
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Sean Cunneen
Blue Island IL
8" f/8 Home built Newt, Discovery mirror, curved vane spider, CG5 Motorized head with Intelliscope DSC, Pier
C102hd CG-4
100mm F4 Cedar Tube RF Refractor
2,3,4,5,6mm Televue Plossls
27T3,33T3,44T3
9-22 Ethos Zoom
NO, I'M NOT SELLING!
|
Jerry Hyman
super member
Reged: 03/29/07
Posts: 120
Loc: Mesa, Arizona
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I am just amazed at the help I can get on this forum!!!!!
Roy, what program are you using for the design?
Again, thanks for the help!
~jerry
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9.25" Celestron carbon fiber SCT
Vixen Super Polaris Deluxe mount
Vixen Super Polaris mount
Burgess BV24 Binos
|
Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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Hi Jerry,
The program is Solid Edge. I'm just a beginner so the balance point will be just a close approximation. It will be interesting to see the CM difference with different eyepieces. Can you weigh your lightest eyepiece and your heaviest eyepiece? Also do you know how much the Moonlight weighs? I found the information on the Telrad at Company Seven.
Here is a simple idea for the mirror cell. Made from birch 3/4 ply. Inputs welcome.
Roy
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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Weight of mirror and cell.
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Roy McCoy
professor emeritus
Reged: 10/13/05
Posts: 601
Loc: Glendale, AZ
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To get the fan flush with the end of tube, I moved the face of the mirror to 4.33 inches. Again inputs welcome.
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itslifejim
newbie
Reged: 09/23/08
Posts: 1
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My first ever post…
Only yesterday I was trying to work out the centre of mass for a 6” split ring equatorial (it’s a long term project with many very long breaks!), I did it using the rule of levers and a very basic spreadsheet…
Attached is a simple example in Excel
Basically you exploit the Goal Seek tool
It’s quick and dirty but works OK…
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