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The Making of my 20" telescope for a Carl Z mirror

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#1 ctcables

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Posted 25 March 2013 - 12:18 AM

So not sure how all this is going to turn out but we will see.

The Project: Make a telescope to hold a F4.5 20.03" by 1" thick 22lbs quartz mirror being made by Carl Z with a Lockwood 3.5" Flat.

Photos of work done to this point, will add as I get more done.
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To help with weight I have used carbon fiber over balsa. Very light and very strong.
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For the rings I am using a composit honeycomb board also very strong and very light. The stuf is used in aircraft.
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[img]http://i245.photobucket.com/albums/gg48/ORduner/th_20130322_043516.jpg[/img]
[url=http://s245.photobucket.com/user/ORduner/media/20130322_043340.jpg.html][img]http://i245.photobucket.com/albums/gg48/ORduner/th_20130322_043340.jpg[/img]
I hope when done the telescope with mirror will be under 40lbs

#2 Daud

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Posted 25 March 2013 - 12:49 AM

Whoa, he is back, after 4 years...when can I get a 24" quartz blank form you, Chris ?

#3 ctcables

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Posted 25 March 2013 - 01:19 AM

So changing this post to a list of what people guess for the weight.
Marc 45.7LBS
kfrederick 51.0LBS
ausastronomer 47.4LBS


So NO prize as per CN, sorry wish I could give one out.

#4 mark cowan

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Posted 25 March 2013 - 02:27 PM

I hope when done the telescope with mirror will be under 40lbs


That'd be amazing. I'm guessing 45.7, can you start a contest??

Best,
Mark

#5 ctcables

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Posted 25 March 2013 - 08:55 PM

Sounds like a good plan Mark, what do you think the prize shold be? Nice Quartz mirror blank? Say in the range of 6 to 12 inches? I will see what I have on hand, so start putting your guesses for the final weight.

To inclued telescope, mirror, foucser, finder, secondary,and eyepice. Anyother ideas would be great. Will post photos as I move along with this project.

#6 mark cowan

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Posted 25 March 2013 - 10:26 PM

I'm including the weight of the SIPS Paracorr but no EP...

Best,
Mark

#7 ctcables

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Posted 25 March 2013 - 11:34 PM

Not sure on the paracorr but will be using a fethertouch light which is only .8 lbs. should I include the base with controler? may do a platform for tracking but not sure yet. Going to talk with Dan Gray about what system will work best with what I want to do. Anyway sounds like a fun give away, nice thing to do for all the people that have helped out over the years. So get the weight right and win a quartz mirror blank. Will post size tomarow. Plan on completing the telescope before OSP.

#8 GeneT

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Posted 25 March 2013 - 11:57 PM

Very interesting project. Keep us updated on how things are progressing.

#9 tezster

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Posted 26 March 2013 - 06:49 AM

Wow... that'll be an super light-weight scope for a 20" - my 10" DobStuff weighs just a shade under 40 pounds, and I already consider that fairly light.

This one will be fun to follow :)

#10 ctcables

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Posted 26 March 2013 - 07:06 AM

should this post be moved to ATM, Optics and DIY Forum? It is a reflector but might be better suited in the DIY area? if so how do I move it or should I just restart it? Anyway Lots to do yet but taking my time.

#11 kfrederick

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Posted 26 March 2013 - 07:15 AM

Making things very strong and very light is not very easy . Chris Thanks for the glass I have gotten . I know your telescope will be very nice .A fast 20 is the perfect size . I say 51 lbs .[If no helium is used in the tubes] Ha Ha

#12 ausastronomer

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Posted 26 March 2013 - 04:13 PM

Hi Chris,

I am guessing at 21.5kg which is 47.4lbs.

This is the exact weight of my 10"/F5.3 truss dob, which is designed to be rock solid and steady. It will be a tremendous effort to get a 20" down to that weight.

PS If I win I will pay the freight, after Carl Z turns it into another gem :)

Cheers,
John B

#13 Starman1

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Posted 26 March 2013 - 04:44 PM

I'm including the weight of the SIPS Paracorr but no EP...

Best,
Mark

The SIPS does have the advantage of never having to guess about perfect coma correction, but there are advantages to the "slide-in" Paracorr:
--it parfocalizes all your eyepieces. If the truss poles are cut correctly, you may be able to achieve focus very close to the in-most position of the focuser. This has the advantage of minimizing the secondary-to-focal plane distance and reducing sag in the focuser due to the weight of heavy eyepieces. With the SIPS, your eyepieces will focus over a range.
--it is normally already removed when setting up, so collimation doesn't require removal, unlike the SIPS (some people do remove the SIPS lens when tearing down, but I don't think all do).
--it will never insert beyond the end of the focuser drawtube
--it is threaded for filters on the bottom end, standardizing filter diameter and making it possible to exchange eyepieces without changing the filter from eyepiece to eyepiece
--it can be removed easily and used in another scope so it can easily be shared with others or if you have more than one scope set up.
--Depending on your focuser cost, it might be cheaper in combination with the focuser than the SIPS focuser + Paracorr ensemble.
--it makes correction of an already existent scope easier than changing the focuser.

Obviously, this f/4.5 scope will need a coma corrector. If you build the scope assuming a 31 Nagler and Paracorr in the focuser, overall balance will be pretty good.

#14 ctcables

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Posted 26 March 2013 - 09:21 PM

I have posted a photo of the 6" mirror blank that will be given to the winner. Also I have started a list of guesses and will keep it updated in the 3rd post, this should help people save time. So if you want to see what others have put for weight just go to the first page 3rd post. Good luck.

#15 ctcables

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Posted 26 March 2013 - 09:44 PM

So just got informed that Cloudy Nights needs to give the OK for me to give the blank away. should be ok but if things change very sorry. Will post when I find out.

#16 ctcables

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Posted 27 March 2013 - 11:48 PM

Good news I am allowed to give the 6" blank away to the winner or person that gets near the weight of the telescope.
My rules: Items to be included in weight of telescope!
1: Focuser
2: secondairy, wire spider and secondary cell.
3: 20 inch quartz mirror 1" thick
4: 18pt mirror cell with side support
5: main rotation bearing.
Not included in weight is drive system and telescope platform/stand.

6:deadline to get your guess in is April 30
7: winner of the free 6" quartz mirror blank will be contacted when the telescope is completed I hope before Oregon Star Party. Good luck



#17 ctcables

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Posted 27 March 2013 - 11:55 PM

Post deleted by ctcables

#18 ausastronomer

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Posted 28 March 2013 - 07:17 PM

Hi all,

This thread and giveaway by Chris is all good to go.

Please guess away as you wish.


We have untagged Chris as a vendor as he has wound his business down. There was never any question of Chris's generous intent with this giveaway, but as a tagged vendor it was against the rules and they have to be applied consistently for all vendors.

Good luck in the Giveaway.

Cheers,

#19 ctcables

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Posted 28 March 2013 - 08:02 PM

Hay thank you so much for doing this for me. Back on for the 6 inches blank give away. get the weight right and win this very nice 6" mirror blank including shipping with in the USA.

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#20 ctcables

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Posted 28 March 2013 - 09:27 PM

Very cool delivery to day, just recived my 3.5" Lockwood quartz secondary mirror, wahooo. Around 1lbs.

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#21 ctcables

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Posted 30 March 2013 - 11:33 PM

Good news I am allowed to give the 6" blank away to the winner or person that gets near the weight of the telescope.
My rules: Items to be included in weight of telescope!
1: Focuser
2: secondairy, wire spider and secondary cell.
3: 20 inch quartz mirror 1" thick
4: 18pt mirror cell with side support
5: main rotation bearing.

Not included in weight is drive system and telescope platform/stand.

6:deadline to get your guess in is April 30
7: winner of the free 6" quartz mirror blank will be contacted when the telescope is completed I hope before Oregon Star Party. Good luck

#22 gatorengineer

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Posted 31 March 2013 - 07:44 AM

Chris,

Good Luck, your goals are enviable, but if you are going to use any thing even vaguely approaching a widefield eyepiece (31 Nagler, etc). You wont come in under 70 lbs for the scope that goes to the field with the tailweights needed to balance, shroud, finder, telrad baffles... This is still great accomplishment as a commercial 20F4.5 would be over 100.

I understand the goals of fast cooling and thin mirrors, but that doesnt get away from the need for tailweights and crazy complex mirror supports to get a good image, as thin as your primary is.

Just looking at your sketch, a couple of other things jump out, I dont think your scope will swing through to Zenith (mirror box may be too short). You will need a significant light baffle opposite side the focuser, as you will have stray light issues (this also will add to the need for tail weights (You are around 5:1 distance to focuser versus distance to mirror), so every pound up top will be 5 pounds in the tail. Telrad, finder etc, to make the scope useable all add counterbalance (also the shroud)..... I am on my 5th or 6th large dob (currently a 25 F5 commercially built), but have built several of my own.... I applaud your ingenuity, and drive, and just want to give you a cuople of look outs....

#23 kfrederick

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Posted 31 March 2013 - 07:48 AM

How about Mark C be the judge as to if it is stiff enough .If Mark says it is stiff and you are under 40 lbs I send you a mirror . The X prize The first big telescope who weight is under twice the diameter . Now just get rid of the obstruction. All good fun

#24 ctcables

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Posted 31 March 2013 - 07:58 AM

My 14.5 inch scope is at 32LBS on the scale (no bearing stand just scope) photos can be seen at 2012 OSP. This one is going to be better in every way. I have given up some weight with the wood lam but it looks so nice. Still looking good on weight but we will see. Put your guess in.

#25 ctcables

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Posted 31 March 2013 - 08:10 AM

This is a photo of my 14.5, new telescope is not the same but a combo of it and others I have seen.
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