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Equipment Discussions >> ATM, Optics and DIY Forum

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starman345
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14" Hubble Optics Project
      #5194593 - 04/28/12 09:48 AM

The 14" Hubble Optics mirror has arrived and I'm at the point of making sawdust with the secondary cage construction but I'm having trouble understanding the questions NEWT is asking for input:

Tube thickness- Is this the actual width(not thickness) of the 1/2" baltic birch I'm using for the cage rings? I'm thinking of making them 1.5" to 2" wide, not sure on this yet.

Focuser to front of tube- Is this the distance from the center of the focuser tube to the top of the upper secondary cage ring?

Mirror face to back of tube- Is this the primary mirror in question?

Spare focuser in travel- Not sure what to enter here as I don't really know what it means. I'm thinking it probably has to do with adding a camera later?

I have a 13mm Ethos that I use almost exclusivly in my 10" Skywatcher and expect in the future to add a 6mm and 21mm Ethos as I really like the wide veiws. The Hubble Optics mirror is f 4.48 so I'm wondering about possibly needing a Paracorr and if so how I should tell NEWT about that? Or maybe I could get by without a Paracorr?


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polaraligned
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5194722 - 04/28/12 11:14 AM

Tube thickness is the thickness of the panel that your focuser will be mounted on, NOT the ring thickness. You have the next 3 questions right. Not sure how much, if any, extra backfocus you need for the paracorr

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Mirzam
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Re: 14" Hubble Optics Project new [Re: polaraligned]
      #5194764 - 04/28/12 11:43 AM

A Paracorr needs about 1/2" of infocus. I usually put the focal plane about 3/4" above the fully racked in focuser height if it is a scope that will use a Paracorr.

JimC


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starman345
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Re: 14" Hubble Optics Project new [Re: polaraligned]
      #5195486 - 04/28/12 08:01 PM

Quote:

Tube thickness is the thickness of the panel that your focuser will be mounted on, NOT the ring thickness. You have the next 3 questions right. Not sure how much, if any, extra backfocus you need for the paracorr




Thanks, I'm glad I asked that question, there is quite a difference in measurement between my cage rings width and focuser board thickness.


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starman345
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Re: 14" Hubble Optics Project new [Re: Mirzam]
      #5195507 - 04/28/12 08:21 PM

Quote:

A Paracorr needs about 1/2" of infocus. I usually put the focal plane about 3/4" above the fully racked in focuser height if it is a scope that will use a Paracorr.

JimC




Thanks, is it safe to assume even if I find I don't need a Paracorr I will be alright with 3/4" spare focuser in travel ?
I have a Moonlite 2" focuser presently on my Skywatcher but will be using that on this project.
I've decided on making the cage 10" high with 1/2" thick rings 1 1/2" wide. Changing the various input numbers in NEWT has finally given me acceptable results. See below
NEWT

* 14. inch f 4.48

14. primary mirror diameter
4.48 f ratio
16. tube inside diameter
0.25 tube thickness
0.75 extra focus height
0. camera focus height
2.6 diagonal minor axis
2. focuser height
2. focuser diameter
8. focuser to front of tube
3.5 mirror to back of tube
1. fixed baffles (1 or 0)
inch unit of measure

If anyone notices anything jumping out at them as wrong I would appreciate a heads up...this is all new to me.
I've chosen a 2.6" secondary but could go with a 2.76", NEWT gives the ok for either keeping all the other numbers the same. Is there any advantage of one over the other?
Thanks for the answers so far, I appreciate it.


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sopticals
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5195775 - 04/28/12 11:31 PM

Hi Brian,

I think I would go with a 3.1" secondary. When I set up my 14" f5.07 Hubble Optics mirror powered dob, I instaled a GSO 2.76" secondary. Since going the binoviewer way, with 1.5"-2.0" further infocus required,I moved secondary down tube to achieve this, so light cone size arriving at the secondary being larger, I needed the 3.1" to accommadate this. Also going slightly oversize, deals with edge problems that many secondary mirrors seem to have. In my case, the image quality was improved when I upsized. Could be that the image was better due to my new secondary, (from Hubble Optics), may have been optically superior to the smaller GSO. Any way all the best with the build.

Stephen.


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killdabuddha
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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5195855 - 04/29/12 12:59 AM


I wonder whether 2.6" is enuf too. Have you calculated the illumination values for a 6 or 7mm exit pupil EP? I like Mel Bartels' calculator

http://www.bbastrodesigns.com/diagonal.htm

Also, have a look at Lockwood's chart

http://www.loptics.com/ATM/diagonals.html

Collimation would be easier too. And minimalizing the CO (central obstruction) percentages are sumthin we've all needlessly obsessed over in an effort to tweak every bit of performance outa our scopes, but 3.1" is well within acceptable limits.


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starman345
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Re: 14" Hubble Optics Project new [Re: killdabuddha]
      #5196168 - 04/29/12 09:06 AM Attachment (70 downloads)

Stephen, thanks for the kind words. I'm really enjoying the process of putting this together. Some of the software programs are a bit humbling, Plop mostly, still trying to get my head around that.
Thanks for your experience with your 14" Hubble and secondary sizing, it looks like I should be considering something bigger than 2.6"

Killdabudda:
Thanks for the links, both Bartels and Lockwood's sites give acceptable results for a 3.1" secondary with my 14" primary using my 13mm Ethos with its 22.3mm field diameter.
The only problem I have now is NEWT does not like the 3.1" secondary choice with my setup, it says I now have "vignetting at focuser of 75% ray". I've tried changing the various values in NEWT but can't seem to make the 3.1" secondary an acceptable choice. Any suggestions with that? At this point no actual construction has started yet so I can change anything but the Primary diameter and focal ratio. Or maybe I should just ignore the warning?


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Mirzam
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5196295 - 04/29/12 10:16 AM

Ignore the warning. Also, you will be fine if you allow 3/4" infocus with or without using a Paracorr. At f/4.48 you will likely end up using one though.

JimC


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Dave O
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Re: 14" Hubble Optics Project new [Re: Mirzam]
      #5196371 - 04/29/12 11:19 AM

Yes, the 'warning' is simply letting you know that the light cone including everything that is 75% illuminated (or more); is larger than the 2" diameter of your focuser. This would normally not be considered a 'bad' thing.

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killdabuddha
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Re: 14" Hubble Optics Project new [Re: Dave O]
      #5196484 - 04/29/12 12:23 PM

Yes, as the others say, the vignetting is inconsequential. NEWT gives you the size of the 75% illuminated field and yer field stop is still well within this range. The spare wiggle-room you have--the difference between yer EP field stop and the size of NEWT's 75% illuminated field--is what gives you yer greater ease of collimation, etc. (Moreover, some very knowledgeable people here say that you can even satisfactorily get away with an illumination drop-off down to 50%, but you don't have to worry about that.) I ran yer numbers, 1st thru a telescope calculator for exit pupil and field stop per the 21mm Ethos

http://www.stargazing.net/naa/scopemath.htm

which gives an exit pupil of 4.68mm at a field stop of 36.6mm, then plugged these values into Mel's calculator. Yer fully illuminatin 20 mm with nary (.2) any magnitude drop-off. Let's say you decide later on to really push the exit pupil for good dark sky conditions--max it out to near 7mm exit pupil with a 31mm Nagler for a 1.6* TFOV...At a field stop of 44.4mm yer fully illuminated field hasn't changed, and the illumination drop-off is still less than .3 magnitude at the edge of field. I wish I had yer curves and yer room to maneuver.


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starman345
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Re: 14" Hubble Optics Project new [Re: killdabuddha]
      #5196565 - 04/29/12 01:30 PM

Thanks for the replies everyone, it looks like the choice is a 3.1" secondary. I have materials on hand to construct the secondary cage so that will begin, I think after that is completed I will give the dimensions to Astrosystems for a spider, holder, and 3.1" secondary. They seem to have a good reputation here and elsewhere, maybe there are others just as good?

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Mirzam
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5196718 - 04/29/12 02:58 PM

Astrosystems has excellent spiders and secondary holders, but for the secondary itself I like to have one that comes with test data. That pretty much limits the choice to Protostar or Antares Optics. Protostar also makes nice spiders/holders but their delivery times have been quite long. Maybe they are caught up? Anyone ask them at NEAF?

JimC


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killdabuddha
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Re: 14" Hubble Optics Project new [Re: Mirzam]
      #5197141 - 04/29/12 07:34 PM

Quote:

Astrosystems has excellent spiders and secondary holders, but for the secondary itself I like to have one that comes with test data. That pretty much limits the choice to Protostar or Antares Optics. Protostar also makes nice spiders/holders but their delivery times have been quite long. Maybe they are caught up? Anyone ask them at NEAF?

JimC




Yeah, Protostar and Antares seem to be the consensus choice from everythin I've read here at CN. We woulda gone with one of these. But I would caution against goin overboard here too...the standard secondaries of these are likely to be as good to the eye as any of their others (an Antares 1/14th wave PV will be as good as their 1/30th as far as you can tell, and you'll save $120).

Also, for yer reference, here's a nice list of links/resources

http://stellafane.org/misc/links.html


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SteakFury
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Re: 14" Hubble Optics Project new [Re: Mirzam]
      #5197755 - 04/30/12 07:03 AM

Quote:

Astrosystems has excellent spiders and secondary holders, but for the secondary itself I like to have one that comes with test data. That pretty much limits the choice to Protostar or Antares Optics. Protostar also makes nice spiders/holders but their delivery times have been quite long. Maybe they are caught up? Anyone ask them at NEAF?

JimC




I recently ordered a spider from Protostar. They list a two week lead time but mine shipped in just a couple of days.


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sopticals
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Reged: 03/28/10

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Re: 14" Hubble Optics Project new [Re: SteakFury]
      #5198807 - 04/30/12 06:35 PM

Hi Brian,

Got my spider/secondary holder for my 14" dob from "Meridian Telescopes", fits 16" tube size. Description: 4-vane Spider & Secondary Holder Assembly for 16"ID Tube w/1.8" hub, Unpainted. Price $37.95 plus shipping. Their address: MTG Products LLC, PO Box 571, Mt Clements,MI 48046. Not at all expensive and works well.

Best regards
Stephen.


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starman345
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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5212654 - 05/08/12 07:01 PM Attachment (62 downloads)

I haven't forgotton about this project, I was side tracked with a barn door tracking system replacement. My neighbour enlisted me to help him change to a new system, he figured his 105 year old tube track had paid for itself. Neither of us had ever done anything like that before so it was an education.
Back to ATM:
I've spoken with Astrosystems and Protostar about spiders, holders and secondary mirrors and its just a matter of deciding which, they both seem to be very professional.
Stephen, I e-mailed Meridian Telescopes as they were out of stock on the 16" spider/holder on their wepage, sadly, they are no longer going to stock any more of them(in that size). You got a deal there!
I got a 5x5 sheet of 1/2" baltic birch and have been cutting tube rings. I didn't have a router circle cutting jig so made one but it took four tries to get the inside dimension for the rings just right, a lot of trial and error but its coming.


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5212663 - 05/08/12 07:13 PM Attachment (67 downloads)

Is there a way to attach more than one picture per post?

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sopticals
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Reged: 03/28/10

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5213100 - 05/09/12 12:32 AM

Hi Brian,

Great stuff. Watching your progress with interest.

Best regards
Stephen.


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starman345
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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5214005 - 05/09/12 03:08 PM Attachment (73 downloads)

Spent a little more time with the tools today and produced this. I wanted the cage height to be 10" but I forgot about there being strut seats on both rings so I'm short of 10" by 1/16"...I"ve had bigger disasters

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5214007 - 05/09/12 03:09 PM Attachment (63 downloads)

My jig for cutting four struts all the same length

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5214050 - 05/09/12 03:29 PM

What is the best way to install tube inserts? I ran a 1/4" bolt through a piece of 3/4" oak and fastened an insert up tight then backed it off about 1/4" and tapped it into the tube.A couple of them didn't go in straight, they seem to be tipped to one side. Any way to straighten them out?

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5220171 - 05/13/12 12:33 PM

I"ve been playing with Plop and am wondering what others are using as a thickness value for their Hubble Optics mirror. The selections in Plop are for solid mirrors not the sandwich type that Hubble makes. At least that is what I think, I see "fused silica" is that a sandwich type?

Edited by starman345 (05/13/12 12:35 PM)


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davidpitre
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Re: 14" Hubble Optics Project new [Re: Mirzam]
      #5220445 - 05/13/12 03:32 PM

Quote:

Astrosystems has excellent spiders and secondary holders, but for the secondary itself I like to have one that comes with test data. That pretty much limits the choice to Protostar or Antares Optics.



I believe Ostahowski's secondaries come with a test report:
http://www.ostahowskioptics.com/


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starman345
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Re: 14" Hubble Optics Project new [Re: davidpitre]
      #5220486 - 05/13/12 03:53 PM

Thanks David, I've already ordered a Protostar 3.1", good to know about Ostahowski, I"d never visited that site before.

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thinairart
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5254160 - 06/04/12 01:14 AM

Hi Brian, I just noticed this thread or I would have replied sooner. I also built a truss dob for a 14" Hubble Optics sandwich mirror, completed last October.

The thread for my build is here: 14" ATM DOB

In regards to mirror thickness for PLOP, I found this quote on the datasheet from HO:

Quote:

To be conservative, you can treat the mirror as a solid mirror with equivalent thickness of 1.2"




I ended up with an 18pt cell, which was recommended by HO, but was probably a bit overkill. If you end up going that route and want more details on all the cell dimensions I used, let me know.

One issue I ran into with the 14" HO mirror is that it only weighs 18 lbs (compared to a full thickness mirror at around ~25lbs). So keep that in mind when you are deciding on the height of your mirror box, or you could get into trouble with balance issues.

Another potential gotcha is when calculating the tailgate dimensions, measure the actual diameter of the mirror to account for the ~3/16" bevel around the circumference.

When it comes to edge support, I ended up going with a 2" nylon sling. The channel between layers rules out using a simple cable sling system. I would like to rebuild my mirror cell so that I can use 45 degree edge supports.

For the tailgate I used box channel aluminum and that worked out fine. An advantage of a lighter mirror is that welded steel is nice to have but not a requirement.

That is all I can think of right now, but I'll be watching your progress!


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starman345
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5254364 - 06/04/12 08:44 AM

Quote:

Hi Brian, I just noticed this thread or I would have replied sooner. I also built a truss dob for a 14" Hubble Optics sandwich mirror, completed last October.
The thread for my build is here:




Hi Aaron, thanks for chiming in. I have your ATM build thread bookmarked and have read it over and over many times. Lots of good advice in there. I have to admit, I stole a few of your ideas from that thread.

Quote:

I ended up with an 18pt cell



That is what I"m building as well, I'm waiting on some aluminum to be delivered to get started. I asked the Hubble Optics people about an 18 pt cell for the 14" mirror and they said that would work fine, also a 6 point would work ok, so it seems like the 18 is a bit of overkill as you say but I would rather go that route. I have seen that they use a 6 point with their UL 16" telescope also.

Quote:

One issue I ran into with the 14" HO mirror is that it only weighs 18 lbs (compared to a full thickness mirror at around ~25lbs). So keep that in mind when you are deciding on the height of your mirror box, or you could get into trouble with balance issues.



Thanks for that bit of information, I hadn't even considered the lighter mirror weight. I haven't gotten to the torque calculations yet but will definately keep that in mind--don't know if I mentioned in this thread that I am using the Kreige&Berry book for direction....otherwise I wouldn't even know what torque calculations were for

Quote:

Another potential gotcha is when calculating the tailgate dimensions, measure the actual diameter of the mirror to account for the ~3/16" bevel around the circumference.




This is something I noticed when using PLOP, I had been using the 14" dimension for diameter and after actually measuring I discoverd its really 14 5/16" edge to edge through the center. It made a difference in PLOP.
I have a full size drawing of the cell with the mirror resting in it to help me determine the cell size, hopefully I won't have any disasters there but thanks for the warning, I'll definitly pay attention when figuring the cell dimensions.

Quote:

I would like to rebuild my mirror cell so that I can use 45 degree edge supports.



This is what I've decided on too, Starman1 and Pinbout gave me the idea in some of their posts. Without this forum and the Kreige & Berry book I would not have the confidence to try building this telescope.
I've ordered an aluminum plate that will hold the triangles and bars and also the 45 degree support posts. The plate will be connected to the mirror cell frame by the collimation bolts, that way, when collimating, everything moves together, there should be no binding as I've read happens with a sling..
My Protostar spider and secondary mirror arrived recently and a Stellarvue finder should arrive next week so I can get the weight of the secondary cage and continue on with the build. Thanks for your help.


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careysub
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5254998 - 06/04/12 05:02 PM

In using PLOP you should use the actual thickness of the sandwich mirror for the mirror thickness -- the advantage of any type of hollow core construction is that you get the stiffness of the full thickness at a reduced weight.

For the glass type, the best one to pick may be fused quartz. Why? Well, the glass actually used is soda-lime which is stiffer than pyrex, but about the same as fused quartz; and the fused quartz is lighter (by about 10%) than soda-lime itself so it simulates to a certain extent the lightness of the mirror. However, this selection does not have a very large effect.

I have an HO 18" mirror that is 1.93" thick. I am planning on using a 6-pt cell, which gives me an RMS error of 2 nm, effectively perfect.


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thinairart
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5255067 - 06/04/12 05:52 PM

Quote:

I have to admit, I stole a few of your ideas from that thread.




Steal as much as you like! A lot of my ideas came from other ATM threads as well

Using a two-layer approach to the mirror cell is definitely the way to go if you want to use posts for edge support. I added edge posts to my single layer K&B style cell, and the mirror would bind up on the posts frequently, throwing the collimation completely off.

If you have not looked through a Stellarvue product before, you are in for a treat with the finder you ordered. The image is very crisp, with pinpoint stars and easy focus controls. The model I ordered also supported interchanging the 1.25" eyepiece, which I've found helpful in some situations for star hopping with a bit more magnification.


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starman345
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Re: 14" Hubble Optics Project new [Re: careysub]
      #5255123 - 06/04/12 06:24 PM

Quote:

In using PLOP you should use the actual thickness of the sandwich mirror for the mirror thickness



Full thickness is what I ended up using. Its kind of a *BLEEP* shoot with these Hubble mirrors, PLOP really can't accomodate them. Hopefully I'll get acceptable views with the 18 point but if not I can always re-build the cell...it will be made from aluminum with no welding so should be easy to modify.

EDIT: hehe, *rap got bleeped

Edited by starman345 (06/04/12 06:26 PM)


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5255136 - 06/04/12 06:30 PM

That makes me feel good about the Stellarvue choice, I"ve never looked through one but they seem to be highly rated on the forums and I am tired of going through the contortions of looking through the straight through finder on my Skywatcher. I ordered the F050M2 model. Hopefully I can figure a way to connect it to the secondary cage.

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Pinbout
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5255324 - 06/04/12 09:16 PM

Quote:

A couple of them didn't go in straight, they seem to be tipped to one side. Any way to straighten them out?




I tighten the insert up against the wood. I like using softcore ply wood to hit the inserts in, the soft ply compresses a little more allowing for that last bit of adjustment. as I'm hitting them in I can adjust the insert by hitting on either side, but they don't have to be perfect either.

to straighten them out they will have to go deeper as you straighten them.


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starman345
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Re: 14" Hubble Optics Project new [Re: Pinbout]
      #5255747 - 06/05/12 07:24 AM

Quote:

to straighten them out they will have to go deeper as you straighten them.




Yes, that is exactly what happened, I tapped the high side with a screwdriver and hammer until they were pretty much level all around. I was afraid of getting them too deep and in the way of the spider mounting screws but it turned out ok.


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thinairart
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5256327 - 06/05/12 02:54 PM

I used the Stellarvue finderscope mounting ring kit (#R50A) they recommended for dobs: Mounting rings

I attached the base to a 1"x 1/2" strip of cherry sandwiched between the two secondary cage rings, and that has worked out pretty well. Learning how to align the finder with two rings has been interesting, but I'm slowly getting the hang of it.


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starman345
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5256419 - 06/05/12 03:54 PM

Quote:

I used the Stellarvue finderscope mounting ring kit (#R50A) they recommended for dobs




Great, that's the one I ordered but was unable to see from the picture on their site exactly what the mounting looked like.
I also ordered their tripod mount, my better half loves birdwatching so I may lose my finderscope to her before I get it installed on the telescope


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5263015 - 06/09/12 08:33 AM

I'm going to use 3/8" bolts for collimation and am thinking of going with the Belleville springs. On McMaster Carr there are many different springs for this size with different load ratings..from 110 lbs to 597 lbs. Which would be ok for an 18lb mirror? I don't want to buy something that a tank could drive over and not depress...or something too mushy either

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piaras
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5264805 - 06/10/12 02:09 PM

The way that would work best with Belleville springs is the use a stack of the lighter weigh rated. Depending on which way you stack them you can vary the rating. Mounted with opposing faces they are the normal rating but stack two in the same direction and the rating goes up. The best thing about bellevilles is the way the you can combine the washers to get a rating that you require. We use them in the shop all the time. just remember that you want the washers to be under compression all the time. Start at 90% compression and collimate from there. Also use fine pitch instead of regular course thread, it will give you better control.
Pierre


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5265068 - 06/10/12 05:22 PM

Quote:

I'm going to use 3/8" bolts for collimation and am thinking of going with the Belleville springs. On McMaster Carr there are many different springs for this size with different load ratings..from 110 lbs to 597 lbs. Which would be ok for an 18lb mirror? I don't want to buy something that a tank could drive over and not depress...or something too mushy either




What cell support/collimation arrangement are you planning?

You can use 3 springs supporting the cell, and then a threaded knob travelling on a bolt to push the cell down against the springs for top collimation (I think this what you are proposing). The springs and the bolt/knob arrangements do not need to be collocated (though that works also) - the springs could be under the mirror, with the adjustment push at the mirror edge.

Think about the spring support this way, at vertical the mirror plus cell puts 7 lb of weight on each spring (if the cell weighs 3 lb). The basic adjustment of the mirror should push it down a distance against the spring to add, say, another 7 lb of force. This means that the mirror is being held in place against the collimation adjustment with the equivalent of 1 G of force (rising to 2 G at horizontal); less force could work, but lets make sure the adjustment is firm.

So a spring that takes a load of more than 14 lb is called for, the remaining consideration is how much additional adjustment travel you want/need. If the spring constant) rate is 14 lb/in then you could back off the initial adjustment by 1/4" and still have 1/2 G holding the mirror, and if it had a max load of at least 17.5 lb you would have 1/4" of further travel (>1/2" total).

Consider for example, McMaster-Carr compression spring 9657K323, which is 1" long, compresses to 0.32", has a max load of 29.27 lb, and a rate of 42.80 lb/in. The 14 load would compress it 1/3", leaving 1/3" additional travel, and you could back off up to 1/6" (under the 1/2 G criterion) for 1/2" total travel.

Belleville springs are interesting, but I am not sure they are the best choice for this. For one thing their working load of range of compression is much less - the above spring will compress for 2/3 of its length (and 1/2 usefully), whereas few Belleville springs compress more than 1/4 at working load, thus for any working distance the Belleville stack will be twice as tall (or taller).

BTW - the bolts don't need to be so heavy, you can get finer threads in 1/4", and if you separate the spring "rail" (which would bear the weight of the mirror plus cell) from the collimation you could go a lot finer in the thread (10-32 maybe).


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starman345
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Re: 14" Hubble Optics Project new [Re: careysub]
      #5265890 - 06/11/12 08:49 AM

I think I'll order some Belleville springs and also some regular compression springs and experiment with both, they really don't cost that much anyway.
I'm mounting everything...triangles/bars, 45 degree whiffletree supports and mirror retaining clips to a 1/4" thick aluminum plate and then have three collimation bolts between the plate and the frame of the cell (1 1/4" angle alum with 1x1 alum sq tube for crossbars) that will be bolted to the mirror box sides.
Finer thread bolts is a sensible approach for collimation, I'll go with that and maybe a bit smaller than 3/8" bolts. I'm having a hard time finding fully threaded bolts locally, probably have to order them too, also the all metal lock nuts that K&B reccommend are rare here...
Thanks for the tips guys


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piaras
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5266696 - 06/11/12 04:29 PM

You should be able to find full thread shafts at hardware stores like Kent, Home Hardware etc, or full thread bolts at auto dealers or go to your local scrap yard. Every where else any bolt over 1" will not have full threads.

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starman345
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Re: 14" Hubble Optics Project new [Re: piaras]
      #5266911 - 06/11/12 06:46 PM

Quote:

Every where else any bolt over 1" will not have full threads.




yes, that's what I'm finding, today I was in the US and found full threaded bolts and all metal locking nuts at a True Value Hardware store, so now I have a source


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thinairart
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5295733 - 06/30/12 01:01 AM

A few posts back Careysub offered an example compression spring for use in your mirror cell. I've been meaning to change out my weaker springs to fix slight collimation drift near the horizon & zenith, so I gave that recommendation a try.

Here is the link to that spring: http://www.mcmaster.com/#catalog/118/1220/=i73oua

I installed the new springs this week and am happy to report they work great! The spring has a 1" diameter so it fits nicely between the steel bars of the mirror cell the & 1" box channel I used for my tailgate rungs. And my collimation drift has been solved, with no appreciable drift between about 10 - 80 degrees.

So if your looking for a good spring to support the Hubble 14" mirror, something similar should work great.


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starman345
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5296271 - 06/30/12 12:04 PM

Hi Aaron, I ordered those springs Careysub suggested and McMaster-Carr sent them and just before they were delivered they issued an intercept to return to sender. A subsequent e-mail explained they could not deliver "Due to the complexity of U.S. export regulations"....even though I had supplied my US shipping address, I thought it was a bit strange but they can choose their customers.
I've been searching other sources for compression springs but can't seem to find anything close to Careysub's recommendations.
The part number on McMaster-Carr is 9657K323. Anyone know where I can get that spring or something close to it?

Aaron, are you using a sling or did you change your cell setup?


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m. allan noah
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5296369 - 06/30/12 01:27 PM

Walk into a locally owned transmission rebuild shop, and ask for springs. They usually throw away a couple dozen on any rebuild.

allan


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thinairart
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Re: 14" Hubble Optics Project new [Re: m. allan noah]
      #5297963 - 07/01/12 02:04 PM

That is pretty weird regarding exporting compression springs, I never would have guessed that would be a problem.

I'm still using a sling for support, but I recently changed it out for a 2" version. I had been using a 1.5" nylon strap that I just didn't feel had enough coverage on both layers, and was drawn in a bit in the middle where the gap is. So if you are going to go the sling route as well, I'd recommend a 2" strap to ensure both layers are well supported.


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starman345
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5301095 - 07/03/12 06:40 PM

I bought a piece of 1.5" webbing a week ago but since changed my mind and now am going to go with 45 degree supports....I've changed my mind several times so that may change as well
Pinbout(Danny) made the suggestion to use a piece of laminate with the Hubble mirrors and it sounds like a good idea. I took a look at some kitchen countertop laminate I had left over from a kitchen re-build and I think it would work very well, almost weightless and very strong. Probably need to spot glue it to each plate but it would open the possiblity of using a cable sling and wouldn't sag in the middle between the plates like you say happened with your 1.5" webbing.


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thinairart
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5301624 - 07/04/12 01:03 AM

The laminate option sounds very intriguing. I'd definitely be curious how that works out. Where are you with the dimensions for the mirror box, have you decided on a depth yet?

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starman345
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5301790 - 07/04/12 06:15 AM Attachment (41 downloads)

I haven't done any torque equations yet, I'm still working on the secondary and the mirror cell at the same time. I"ve got to stop reading here, as soon as I decide on one way to do something, I read some other great way that is more appealing and change the plan, never get anything completed that way.
For the focuser board I used your method of dowels to anchor it to the rings, I don't think I'll glue it at all as it is very sturdy as is and plus I can break down the secondary cage at any future date for modifications.


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5301792 - 07/04/12 06:16 AM Attachment (39 downloads)

Focuser board installed.

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5301793 - 07/04/12 06:16 AM Attachment (49 downloads)

Mirror cell, a work in progress..

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5301795 - 07/04/12 06:24 AM

Forgot to mention about the laminate idea, I was thinking a strip 1.5" wide to span the two plates and long enough to cover at least 180 degrees of the mirror perimeter. The only drawback I can see is with the laminate in place air flow will be impeded, so I don't know how that will impact cool down. I guess holes could be drilled in the laminate to help that, but that would probably weaken the laminate....for now I'm going with the supports at 45 degrees

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thinairart
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5302311 - 07/04/12 02:11 PM

Nice job on the secondary cage, looking very sturdy. I was also planning originally to avoid gluing the focuser board into place so I could also disassemble later on if needed. Unfortunately, I had some minor gaps in my measurement, so the fit was not tight enough and I had to lock everything into place with glue. Your assembly looks very tight though, so I'm sure you won't have any issues skipping the glue.

Nice triangles as well on the mirror cell, I'm interested to see your two-layer cell come together. I'm still undecided if I should rebuild my cell, or save the cell rebuild for a future scope project. Now that I have a proper 2" sling in place, I'm planning to perform some star tests near the horizon and see what kind of strain I see from the sling. With these sandwich mirrors it is kind of a mystery how well a sling performs compared to a regular mirror. The sling contacts both layers, and hopefully the average of those points is fairly close to the actual COG of the mirror. When your looking at building your edge posts, keep in mind as well that at least with the 14" I had from Hubble Optics, the layers were not exactly the same size (1/16" difference between top/bottom). So the edge post will need to be constructed in such a way where it can make contact with both halves. Ah the joys of a sandwich mirror! Economical and lightweight, but in the area of edge support not nearly as straight forward as a typical mirror of the same size.


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starman345
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5360108 - 08/09/12 03:16 PM Attachment (45 downloads)

After a long hiatus, I'm back at it. Yesterday I received this in the mail(Thanks Ralph):

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5360113 - 08/09/12 03:18 PM

Having sold my only telescope on Sunday, I don't have a way to try my new toy So now I need to get back to building....

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5360118 - 08/09/12 03:21 PM Attachment (34 downloads)

I decided on a triangle type cell, almost entirely copied from Reiner Vogel's web page..he has some excellent pictures and explanations on how things work there.

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5360125 - 08/09/12 03:24 PM Attachment (31 downloads)

I used supports at 45 degrees. Using dowels initially posed a problem because the upper plate(mirror) is a bit larger than the lower plate. I drilled the upper dowel in the center and placed the uppper plate in contact with it. The lower dowel was drilled off-center about 1/8" and rotated into contact wtih the lower plate. Bolts and star lock washers locked each dowel in place. It seems to hold ok.

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5360130 - 08/09/12 03:25 PM Attachment (25 downloads)

With separate dowels for each plate

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5360134 - 08/09/12 03:26 PM Attachment (33 downloads)

Overall view

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5360136 - 08/09/12 03:27 PM Attachment (30 downloads)

And again

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sopticals
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5360513 - 08/09/12 07:13 PM

Hi Brian,

Your project is coming on nicely. Nice eyepieces. You will be wanting to press on to the finish mark now that you dont have a scope to try out those oculars. I cant imagine being "scopeless" . Continuing to watch with interest.

Best regards
Stephen.


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thinairart
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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5360670 - 08/09/12 08:47 PM

Creative way to handle the different platter diameters! I'm very interested in how those edge supports perform under the stars. Do you find that the edge supports keep good contact regardless of orientation of the mirror (rotating mirror in the cell) ?

You'll definitely have to push on towards finishing the scope now that you are without a scope. That sharp looking Ethos is hungry for photons!


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Ian Robinson
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5360786 - 08/09/12 10:09 PM

Quote:

Creative way to handle the different platter diameters! I'm very interested in how those edge supports perform under the stars. Do you find that the edge supports keep good contact regardless of orientation of the mirror (rotating mirror in the cell) ?

You'll definitely have to push on towards finishing the scope now that you are without a scope. That sharp looking Ethos is hungry for photons!




Me too.

Very interesting how you've tackled edge support.

Q How heavy is the 14" Hubble mirror ?

Q will the timber used for edgesupport be strong enough, wont it tend to compress a bit over time throwing colimation off and making the mirror loose ?

Would teflon or solid aluminium lathed to the correct diameters for the upper and lower platters be better ?


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starman345
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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5361310 - 08/10/12 09:04 AM

Quote:

I cant imagine being "scopeless"




Stephen, its been mostly cloudy since I sold it so I don't miss it, but I know I will the first clear still night....


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starman345
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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5361318 - 08/10/12 09:09 AM

Quote:

Do you find that the edge supports keep good contact regardless of orientation of the mirror (rotating mirror in the cell) ?



Yes, they do seem to be in good contact regardless of rotation. The two plates although different in diameter, seem to be centered in relation to each other. Is your's similar or are the top and bottom off-set?


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starman345
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Re: 14" Hubble Optics Project new [Re: Ian Robinson]
      #5361344 - 08/10/12 09:23 AM

Quote:

Q How heavy is the 14" Hubble mirror ?



My 14" is 17 lbs 11 ozs

Quote:

Q will the timber used for edgesupport be strong enough, wont it tend to compress a bit over time throwing colimation off and making the mirror loose ?



Good question, I don't know the answer, the dowels I used are older and dried out minimizing shrinkage but I think a more solid material would be a better choice.
Quote:

Would teflon or solid aluminium lathed to the correct diameters for the upper and lower platters be better ?



I think with the difference in diameters of upper and lower platters, something that can be adjusted would be more ideal. I had thought about nylon bolts threaded through a bigger upright support bolt, one nylon bolt for upper plate, one for lower. I may try that later if the dowel idea fails.

There are several challenges with these mirrors, not only the individual edge supports but also there is really no way to find COG...at least that I know of. Also my upper plate is quite a bit thicker than the lower one
And to top it off, the Hubble is about 25% lighter than a conventional solid mirror causing balance issues


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Pinbout
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5361485 - 08/10/12 10:50 AM

Quote:

Good question, I don't know the answer, the dowels I used are older and dried out minimizing shrinkage but I think a more solid material would be a better choice.





paint the wood and put some teflon on them.

grey pvc rods are tyically used at those locations when doing a sling, to stop the sling from sliding side to side.

I like your solution btw.


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starman345
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Re: 14" Hubble Optics Project new [Re: Pinbout]
      #5361639 - 08/10/12 12:33 PM

Quote:

paint the wood and put some teflon on them.




I don't follow? teflon on the dowels? Pieces of teflon? Or something else?


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Pinbout
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5361682 - 08/10/12 01:02 PM

Quote:

teflon on the dowels? Pieces of teflon?




Oui. you don't want the painted wood giving friction to the edge.


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Gene7
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Re: 14" Hubble Optics Project new [Re: Pinbout]
      #5362410 - 08/10/12 08:32 PM

Starman:
Oh yes, very nice scope and beautiful machine work. I also have a Hubble 14 inch mirror that is not yet in a scope. It looks similar, but the two disks are about the same size but are off-set by perhaps a 1/16 inch. Have been figuring how to best support them. Sorry, I am not at all comfortable with what I have seen as solutions so far. I think it is necessary that the weight be divided equally, as all other support components of the mirror are.

My current plans are to shim the edges of the mirror so they are both the same height at the support points and devise a simple lever clip that slides on a support cable to keep the load distributed equally. Perhaps 5 or 7 clips would be used.

Another solution for your support method would be to use a medium soft rubber dowel section, a different size for each side. Thus you could get very close to equal support for each slab, which can not be done with rigid wood or plastic dowel sections. Thanks again for posting the lovely work. Gene

Edited by Gene7 (08/10/12 08:34 PM)


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starman345
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Re: 14" Hubble Optics Project new [Re: Gene7]
      #5362972 - 08/11/12 08:18 AM

Hi Gene, thanks for your comments, all ideas are very welcome.

Quote:

It looks similar, but the two disks are about the same size but are off-set by perhaps a 1/16 inch.



It seems these mirrors are not all the same, I think Aaron(thinairart) mentioned his is similar to yours, mine on the other hand is not off-set, but there is a difference in platter diameter.

Quote:

Sorry, I am not at all comfortable with what I have seen as solutions so far.



Me either, but for lack of a better idea I'm forging ahead with an eye to re-doing things later if need be

Quote:

I think it is necessary that the weight be divided equally, as all other support components of the mirror are.




Yes, I agree here, but how to do that? My upper platter is significantly thicker than the lower one and just a bit larger in diameter...how to figure where COG is? Where and how much pressure do you put on each platter to equalize and how do you accomplish that accurately?
Pictures I've seen of the Hubble Optics UL16 shows they use a simple sling spanning both platters, nothing fancy, so I wonder if all the fussing I'm doing over this support issue is warranted at all.

Quote:

My current plans are to shim the edges of the mirror so they are both the same height at the support points and devise a simple lever clip that slides on a support cable to keep the load distributed equally. Perhaps 5 or 7 clips would be used.



This sounds interesting, can you give more detail? Are you talking about a cable sling? I'm not sure what you mean by lever clips?

Quote:

Another solution for your support method would be to use a medium soft rubber dowel section, a different size for each side. Thus you could get very close to equal support for each slab, which can not be done with rigid wood or plastic dowel sections. Thanks again for posting the lovely work.




Would soft rubber deform over time and introduce friction?
I ordered 1" PVC rod yesterday to replace the wood dowel, I thought that would be less likely to deform and not so susceptable to humidity and temperature changes.
Thanks for the comments Gene, gives me food for thought


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5478788 - 10/19/12 12:55 PM Attachment (36 downloads)

I'm trying to decide how to mount my Stellarvue finder to the secondary cage. Looking at pictures of various setups here and on other forums most people seem to use some type of post installed just for the finder. I'm using 1" hollow tube to separate the cage rings, same material I'm using for the truss tubes..why couldn't I drill a couple of holes in the tube and mount the finder directly to the tube nearest the focuser? I'm just wondering if there is a down side to doing this, since I dont' see it being done. Opinions? I just have the finder leaning against the tube in the picture, trying to show where I'd like to position it.

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derangedhermit
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5479055 - 10/19/12 03:47 PM

Please tell me why you decided to orient the focuser knobs as they are.

There is an alternative for your secondary cover, especially popular in the southern US. It costs three times as much, but some people find the expense worth it. The product is called Blanton's.


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derangedhermit
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Re: 14" Hubble Optics Project new [Re: derangedhermit]
      #5479074 - 10/19/12 04:01 PM

It looks to me like an easy alternative for this type mirror would be to hang it, instead of sitting it on something. Has anyone checked to see if two hanging points, 90 degrees apart, might work? I'd want to consider small cable loops around two of the interior posts on the mirror, attached to two posts.

EDIT: I mean for edge supports.


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starman345
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Re: 14" Hubble Optics Project new [Re: derangedhermit]
      #5479084 - 10/19/12 04:11 PM Attachment (23 downloads)

Quote:

Please tell me why you decided to orient the focuser knobs




You are right, the focuser is upside down, I guess, if there is a "right side up" but it really doesn't matter, knobs still work. If I mount it the other way I don't have clearance for my upper truss connector cam action lever.


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5479152 - 10/19/12 05:12 PM Attachment (23 downloads)

I went with 1" solid PVC instead of wood dowel that I had used in the beginning. I don't know how hanging the mirror from the internal posts would work. It might be fine.
Any opinions on connecting my Stellarvue finder to the 1" tube?


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5479870 - 10/20/12 02:58 AM

If you're sure that's where you want it, I don't see anything wrong with drilling holes and mounting it there. At worst you move it later and have a few holes, or replace the tube section.

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Re: 14" Hubble Optics Project new [Re: derangedhermit]
      #5480411 - 10/20/12 01:34 PM

Yea, I think I'm going to try it on the tube. I really don't want to add another piece to the secondary cage it is already pretty heavy.

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Re: 14" Hubble Optics Project new [Re: derangedhermit]
      #5480531 - 10/20/12 02:48 PM

Quote:

It looks to me like an easy alternative for this type mirror would be to hang it, instead of sitting it on something. Has anyone checked to see if two hanging points, 90 degrees apart, might work? I'd want to consider small cable loops around two of the interior posts on the mirror, attached to two posts.

EDIT: I mean for edge supports.




Although I cannot rule out the possibility that this will work - I would bet against it. For one thing, the support has to be (effectively) very, very close to the COG plane of the mirror. I cannot think of a reliable way of even determining where that is in the post-filled gap between the mirror plates.* Even if you knew it, could you actually secure a cable in the correct position? And would you have any confidence that supporting the mirror weight at two interior posts (located somewhat randomly, not precisely designated) would create an astigmatism free stress pattern in the mirror surface?

The only reason I have confidence in the 90 degree two-point schemes are the FEM and experimental data to back them up.

I suggest the best may to support these mirrors is a vertical whiffle-tree, supporting the front and back plates so that the mirror will level out on its own. For my 18" HO mirror I really have no choice but to pursue this option since the front and back plates have different diameters, but I think it might be the most reliable method for all large HO mirrors.




*Well I can, but it would be difficult. Determine the volumes of the glass for front and back plate, and post layer using Euclid's method of displacement, then mathematically model the mirror and determine where the mid-plane must be.


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Re: 14" Hubble Optics Project new [Re: careysub]
      #5480961 - 10/20/12 08:33 PM

Quote:

Well I can, but it would be difficult. Determine the volumes of the glass for front and back plate, and post layer using Euclid's method of displacement, then mathematically model the mirror and determine where the mid-plane must be.



The longer I ponder on how to support this mirror the more I realize how complex it could be to do it properly, if that is possible at all. I was looking over my 14" HO mirror tonight, it has one plate bigger in diameter than the other, that being the "mirror" plate but of course it has a curve in it so probably doesn't contain any more glass (or much more) than the flat thinner plate on the back. The plates have 96 posts separating them, varying from 15mm to 16mm in diameter, at least that is what my calipers say on the ones at the edge that I can get at. That is a lot of calculation right there, and you would have to assume all the remaining out of reach posts are the same average size.
I thought about a wiffletree type support, it seems logical with all the variables that it would be best just to arrange something to let the mirror come to its own balance point..but at my stage of telescope building experience(baby stage) it seems beyond me. I've found myself laying in bed at night trying to figure out how to support this d**n mirror. Life needs to move on, I really miss my scope so need to get this functional...so, I'm going with the PVC supports at 45 degrees for now. If you design something for your 18" HO I would be very interested in seeing it. One good thing about being an ATM'er....you can always change things down the road


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5481178 - 10/20/12 11:14 PM

I'll send you a sketch of my plan for the vertical whiffle-tree edge support, with a few variations. Not really very complicated.

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derangedhermit
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Re: 14" Hubble Optics Project new [Re: careysub]
      #5481234 - 10/21/12 12:21 AM

Quote:

Although I cannot rule out the possibility that this will work - I would bet against it. For one thing, the support has to be (effectively) very, very close to the COG plane of the mirror. I cannot think of a reliable way of even determining where that is[...]

The only reason I have confidence in the 90 degree two-point schemes are the FEM and experimental data to back them up.




Yes, it's likely it won't work; but it seems simple enough to try, given that other solutions appear non-trivial, and these mirrors represent a great opportunity.

The basic assumption is that hanging a solid mirror at 2 points does at least as well as resting the mirror on two points. Intuitively, that seems a reasonable assumption to me, worth checking by FEM.

Like you, I want to know if anyone had modeled a hanging (solid) mirror, testing for sensitivity close to 45 degrees and front-to-back. If it's not too touchy, then proceed with an empirical test.

Practically, put the cable anywhere repeatable front-to-back and star test - potato-chip over the entire surface is easy to distinguish from other errors; it goes from oval in one orientation to oval 90 degrees away on the other side of focus (I assume that would be the main error when off f-t-b CoG). Adjust as needed.

Or not; it just seemed like an easy solution to build solidly if it worked out.


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Re: 14" Hubble Optics Project new [Re: derangedhermit]
      #5481924 - 10/21/12 01:14 PM

Quote:



The basic assumption is that hanging a solid mirror at 2 points does at least as well as resting the mirror on two points. Intuitively, that seems a reasonable assumption to me, worth checking by FEM.

Like you, I want to know if anyone had modeled a hanging (solid) mirror, testing for sensitivity close to 45 degrees and front-to-back. If it's not too touchy, then proceed with an empirical test.




Seems like it would even simpler to try a 90 degree support that directly engages the posts. Cut a semi-circular notch in a support strut of some kind. Due to the somewhat disorderly positioning of the posts they would have to be custom cut for each side. The problem of finding the COG plane would be the same (though adjusting strut positioning might be easier than cables).

But when supported a sheet mirror at the edge, you are only putting two edge points of a continuous strong, rigid body under local compression. With the posts you are putting a shear load on the post attachment points that they were never intended to take, which is then transferred to two points at the back of the actual mirror surface, sort and extreme case of a "glued" mirror. Very different.

The post attachment points might not even be strong enough to take that load.

For a sufficiently small Hubble Optics mirror one would be very tempted to simply glue the mirror to the cell and avoid these edge support issues entirely.

My 18" mirror is too large to do this, even cranking it up to 18 points of support (6 is fine with edge support), gluing in gives me a Strehl reduction of 0.90 at 45 degree tilt, and 0.82 at 80 degrees.

(Who observes 10 degrees above the horizon? I do, when chasing those elusive southern latitude objects, like Omega Centauri. Not the greatest viewing, but I would rather see what the atmosphere allows without my telescope getting in the way).


Edited by careysub (10/21/12 02:43 PM)


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Re: 14" Hubble Optics Project new [Re: careysub]
      #5482047 - 10/21/12 02:29 PM

Quote:

I'll send you a sketch of my plan for the vertical whiffle-tree edge support, with a few variations. Not really very complicated.




Thanks, much appreciated!


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5482081 - 10/21/12 02:54 PM

Quote:

Quote:

I'll send you a sketch of my plan for the vertical whiffle-tree edge support, with a few variations. Not really very complicated.




Thanks, much appreciated!




How thick is your 14"?

Have you looked into how well you can do with adding support points and gluing into the cell? It doesn't work well enough with my 18" (thickness ratio about 9:1) but it might for yours.

Assuming your mirror is 40mm thick (same ratio) and you built an 18-pt cell and glued it in the Surface RMS at a 60 degree tilt is 9 nm, giving a Strehl reduction of 0.95. Not too shabby. Even at 75 degrees tilt it is 10.1 nm, or S=0.938.


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Re: 14" Hubble Optics Project new [Re: careysub]
      #5482152 - 10/21/12 03:41 PM

My mirror is 40.45mm thick giving a TR of 8.8:1 I'd never thought of glueing to the points. Glueing always seemed counter intuitive to me but I see what you are proposing might be a viable alternative. If the supports at 45 degrees are a failure I can easily unbolt them from the cell, remove them and glue each of the 18 points to the mirror surface. I've noticed that Dennis Steele does this with his hubble mirrors.
Thanks! this would simplify things for sure


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5482406 - 10/21/12 05:44 PM

Using your actual mirror thickness, and secondary size, my tweaked calculation gives 9.86 nm RMS at 75 degree tilt, and S=0.94 (also S=0.95 at 60 degrees, and S=0.97 at 45 degrees).

Looks good.


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Re: 14" Hubble Optics Project new [Re: careysub]
      #5483475 - 10/22/12 11:39 AM Attachment (30 downloads)

I made a jig for drilling holes through the 1" tube for connection of my finder scope, bolted the base to the tube with two 1 1/2" 8x32 screws and nuts. I was afraid I might not be able to tighten the nuts enough to hold the heavy finder steady without crushing the 1" tube but everything turned out fine.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5483479 - 10/22/12 11:40 AM Attachment (29 downloads)

And with the finder mounted. I wonder how it will hold up after I hit my head on it in the dark a few times?

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5483733 - 10/22/12 02:05 PM

If you have any leftover tube, you could cut a piece about twice the length of the distance between the two nuts. Cut that piece in half. Drill two holes matching the bolt holes to make a large saddle washer that goes under the nuts. That should prevent buckling or tearing.

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Re: 14" Hubble Optics Project new [Re: careysub]
      #5483739 - 10/22/12 02:11 PM

Quote:

Seems like it would even simpler to try a 90 degree support that directly engages the posts. Cut a semi-circular notch in a support strut of some kind. Due to the somewhat disorderly positioning of the posts they would have to be custom cut for each side. The problem of finding the COG plane would be the same (though adjusting strut positioning might be easier than cables).

But when supported a sheet mirror at the edge, you are only putting two edge points of a continuous strong, rigid body under local compression. With the posts you are putting a shear load on the post attachment points that they were never intended to take, which is then transferred to two points at the back of the actual mirror surface, sort and extreme case of a "glued" mirror. Very different.

The post attachment points might not even be strong enough to take that load.




You're right, it would be easier, and in either case, the posts might break or break loose. I thought the small loops would reduce potential side loading. I don't see an easy way to do that at the bottom. Thanks for considering it.


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starman345
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Re: 14" Hubble Optics Project new [Re: derangedhermit]
      #5483798 - 10/22/12 02:47 PM

Quote:

If you have any leftover tube, you could cut a piece about twice the length of the distance between the two nuts. Cut that piece in half. Drill two holes matching the bolt holes to make a large saddle washer that goes under the nuts. That should prevent buckling or tearing.




Brilliant!, I'm going to do just that, thanks


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5485150 - 10/23/12 12:06 PM Attachment (34 downloads)

Done! that noticeably stiffened things up.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5487071 - 10/24/12 02:01 PM Attachment (34 downloads)

More progress today, I installed the Protostar flockboard or whatever its called inside the secondary cage. I was nervous about doing this. According to the K&B book put the Kydex in the freezer first..since this isn't Kydex I'm using but Protostar I didn't know if I needed to do that or not. It was quickly evident that wouldn't work. As soon as I took it out of the freezer condensation began to form on it so no way it would stick to the tape on the inside of the secondary rings. So..I wiped it down, by this time it had warmed a bit so I began...
I used carpet tape on the secondary rings, outdoor carpet tape, that stuff is really sticky, hope I never have to take it off.


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5487074 - 10/24/12 02:03 PM Attachment (31 downloads)

Since I could find only 1 1/2" wide tape I had to trim it with my utility knife, got glue goo all over the blade and had to clean it a few times but got it done.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5487078 - 10/24/12 02:06 PM Attachment (31 downloads)

Finally the big moment, I had to un-roll the Protostar onto the sticky tape, had to get it right the first time as there is no way to un-stick that stuff without pulling the tape off the secondary rings. It went ok, I had to trim off about 1/8" in a couple of spots but I think it was more good luck than good management.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5487495 - 10/24/12 07:05 PM

Hi Brian,

Your on the steep learning curve (gets a little "slippery" at times).Keep up the good work (looks like your winning).

Stephen.(Down under 44deg.S.)


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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5487550 - 10/24/12 07:47 PM

Thanks for the words of encouragement. Yes, steep learning curve for sure, a lot of things I've had to re-do because I didn't do it right the first time. I'm going to have a lot of extra pieces and parts leftover when-if this telescope ever gets finished

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5488651 - 10/25/12 01:39 PM

Great progress Brian! Your scope project is starting to come together. I think your solution for mounting the Finder will work great. I used a separate post and in retrospect I would mount directly to the nearest tube if I did it again, saves the extra work.

The Protostar stuff is really nice. I used contact cement to install mine, which was a little more forgiving then sticky tape, but not by much.

Looking forward to seeing the rest of this project come together.


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Re: 14" Hubble Optics Project new [Re: thinairart]
      #5488917 - 10/25/12 04:29 PM

Thanks Aaron, yes, the Protostar material is nice, it is really black, black on the inside. The K&B book said to cut the material a couple of inches too wide and trim it after install but I took a chance and cut it the actual depth of the secondary cage, it worked out nicely and I think I would do it that way again. The piece I received from Protostar was 21" wide, my secondary cage 10 deep so I now have a piece left over that is 11" wide so I can use it on another scope.
I know you had some improvements you were thinking of doing to your dob, have you moved ahead with any of them yet?


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545599 - 11/29/12 02:00 PM Attachment (21 downloads)

The mirror box has been under construction. First I cut the panels from 1/2" baltic birch and cut the various dadoes for everything to interlock.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545601 - 11/29/12 02:02 PM Attachment (46 downloads)

Then all inside surfaces were painted flat black and outside surfaces were given several coats of polyurethane.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545609 - 11/29/12 02:06 PM Attachment (33 downloads)

Then the glue up. I had to really move along to get glue on all the surfaces needing it and get things assembled and squared before the glue dried. Worked out nicely, but I think I would have used slower setting glue had I realized how much time it would take.
Mirror box glued up...no screws, nails or other hardware, just glue and tongue and dado joints


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545617 - 11/29/12 02:12 PM Attachment (40 downloads)

Cell finally gets a fit in the mirror box. This was where I had to do a lot of head scratching. I spent quite a while getting the mirror/cell centered in the mirror box, finally I used string lines corner to corner to locate the mirror donut while in the cell and mounted in the mirror box. This allowed me to secure the cell to the mirror box in the right position. After I figured that out things went a little quicker.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545625 - 11/29/12 02:17 PM Attachment (37 downloads)

Today I put the mirror in the cell, I was a bit concerned there wouldn't be room for my fingers when lowering the mirror into the cell but there was lots. I adjusted the collimation bolts to get smooth action before putting the mirror in the cell but now with the weight of the mirror the action is not so smooth. It definately needs improvement. The bolts will turn but it takes some effort.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545629 - 11/29/12 02:20 PM Attachment (36 downloads)

Now I need to make a mirror box cover and make something to anchor the secondary cage and mirror box so I can take it outside and see where my eyepieces focus.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545763 - 11/29/12 03:58 PM

Did you post a picture of your cell with side-supports? I looked through most of the links but didn't see one.

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Re: 14" Hubble Optics Project new [Re: careysub]
      #5545825 - 11/29/12 04:44 PM Attachment (40 downloads)

I probably didn't. There are no side supports, only the supports at 45 degrees and one other at the top of the cell to keep the mirror from tipping forward. This is the cell when I had fashioned wooden dowels as contact points....

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5545828 - 11/29/12 04:45 PM Attachment (39 downloads)

Since then I have changed out the wooden dowel for PVC..

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5546321 - 11/29/12 09:50 PM

that hubble optics mirror is interesting. definitely soda lime clear glass looks like two pcs of 1/2" or 5/8" (12mm or 15mm) clear glass glued together with UV glue and some sort of spacer piers.

neat concept, should cool rapidly for a mirror that thick.

btw i work in the architectural flat glass industry.


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5546322 - 11/29/12 09:50 PM

double post :S

Edited by frito (11/29/12 09:51 PM)


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Re: 14" Hubble Optics Project new [Re: frito]
      #5546358 - 11/29/12 10:14 PM

Its all coming together really nicely Brian. All the best with the remainder of the construction. Im sure you will be pleased with the HO primary.

Best regards,
Stephen.(44deg.S.)


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Re: 14" Hubble Optics Project new [Re: frito]
      #5546460 - 11/29/12 11:40 PM

Quote:

that hubble optics mirror is interesting. definitely soda lime clear glass looks like two pcs of 1/2" or 5/8" (12mm or 15mm) clear glass glued together with UV glue and some sort of spacer piers.




The piers are soda-lime glass also (naturally) and I had supposed they were fused in a furnace. But you could glue glass as easily than anything else.

Quote:


neat concept, should cool rapidly for a mirror that thick.

btw i work in the architectural flat glass industry.




One comment I have about HO's execution of this concept is that the pier cluster is pretty thick, and they seem to be randomly (if densely) scattered about.

Granting that this is no doubt perfectly adequate for the engineering requirement, I am surprised that they don't use a uniform grid - an optimized grid has got to give a better weight savings and a more uniform product, and placing the glass cylinders into a spacing template seems like it might even save effort overall.

I have corresponded with someone with an HO mirror who was having it refigured and the (highly regarded) optician was having trouble with its surface due to some sort of non-uniformity in this surface properties. My suspicion would lie in the lack of positioning control of the support piers.


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Re: 14" Hubble Optics Project new [Re: careysub]
      #5546480 - 11/30/12 12:00 AM

or improperly annealed glass perhaps.

the company i work for buys plently of glass from overseas. one the the biggest problems with many of the Chinese flat glass manufactures tends to be poor annealing of their heavier glass thicknesses. i have no doubt looking at photo's of the HO mirrors that they are using mass produced soda lime float glass on those mirrors. the 3 un-figured surfaces would not be clear enough to see the support piers clearly if it was not float glass because in a telescope mirror there is no reason to do any surface polishing or smoothing yet those other 3 surfaces appear to be very smooth to me. HO does say the glass is fused together and that would make sense i suppose looking at the photo's of the mirror the rear surface esp. shows a dull but smooth surface indicating that the glass was put into a kiln and heated at some point. the surface reflections i can see on the inner 2 surfaces appears much smoother and more like float glass. plus there is the whole the only reason soda lime glass is significantly cheaper than borosilicate glass types (pyrex) is because its mass produced in a much greater number and there's no reason not to use it


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Re: 14" Hubble Optics Project new [Re: careysub]
      #5548679 - 12/01/12 12:10 PM Attachment (33 downloads)




Quote:

I am surprised that they don't use a uniform grid - an optimized grid has got to give a better weight savings and a more uniform product, and placing the glass cylinders into a spacing template seems like it might even save effort overall.





Mine seems to have a uniform grid. Maybe I'm missing what you are saying here? BTW I measured the pier in the center and it is dead on in the center from my measurements to the mirror edge in several places. I'm curious, does your 18" look similar?


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frito
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5548990 - 12/01/12 03:38 PM

looks pretty uniform to me, if you look at it the wrong way though i could see how one might think its not

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Re: 14" Hubble Optics Project new [Re: frito]
      #5559607 - 12/07/12 04:59 PM Attachment (36 downloads)

I built a gizmo to hold the mirror box and secondary cage in rough alignment and took it outside to see where my eyepieces came to focus. I was astounded when putting in the 21mm stars appeared!
I had calculated where the optics should be placed but I didn't expect things to go that well. All three, 21mm, 13mm and 6.7mm came to focus at the same distance. I am going to take it out again just to make sure, I ran out of time last night and I want to try things with my camera in the focuser to see if I have enough travel.
Dont' laugh at the picture, I know its not a thing of beauty.


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5559803 - 12/07/12 06:49 PM

Quote:

I built a gizmo to hold the mirror box and secondary cage in rough alignment




your thingy is very cool.

Quote:

All three, 21mm, 13mm and 6.7mm came to focus at the same distance.




most of my eyepieces focus around the same, except my tv 40mm plossl, that eyepiece uses almost all of my racked out focuser travel.


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Re: 14" Hubble Optics Project new [Re: Pinbout]
      #5575742 - 12/17/12 01:40 PM Attachment (25 downloads)

I built some lower truss connectors out of several layers of glued up 12mm ply. Drilling the angled holes for the truss poles was a challenge. My drill press table required several adjustments on sacrificial trial blocks before I finally got the required 9 degrees. Besides the truss angles, because the secondary truss connectors were an inch or so wider than the lower connectors I also had to adjust for a small amount of tilt. Sort of like doing a compound miter, only on a drill press. I installed the T-nut on the back, then cut out the chock. A picture of the glued and clamped connector..

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5575744 - 12/17/12 01:42 PM Attachment (20 downloads)

And with the clamps removed

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5575750 - 12/17/12 01:46 PM Attachment (22 downloads)

With the chock installed and a view of the T-nut on the back of the connector

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5575755 - 12/17/12 01:47 PM Attachment (39 downloads)

Truss poles and cam clamp installed

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5575757 - 12/17/12 01:49 PM Attachment (39 downloads)

All the connectors and truss poles assembled

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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5575762 - 12/17/12 01:51 PM Attachment (47 downloads)

With the secondary cage connected. Its starting to look like a telescope!

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sopticals
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5576006 - 12/17/12 04:41 PM

Good progress Brian. You will be looking forward to the night of first light. Nice tidy work shop.

Stephen.(44deg.S.)


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Pinbout
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5576019 - 12/17/12 04:48 PM

Quote:

Truss poles and cam clamp installed




very clean.


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Re: 14" Hubble Optics Project new [Re: Pinbout]
      #5576297 - 12/17/12 07:46 PM

It's been a while since I last looked at Kriege's book, but you seem to be following it closely. I'm in the process of making a 7" mirror and will probably make a miniature version of his design. I'm giving some though to making the truss clamp blocks by sand casting aluminum a-la Gingery instead of out of wood (though I'd have to make wooden patterns to make the sand molds!).

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starman345
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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5576854 - 12/18/12 06:53 AM

Quote:

Good progress Brian. You will be looking forward to the night of first light. Nice tidy work shop.




Yes, while I like using my binoculars its just not the same as a telescope, first light will not come too soon for me. The workshop is the basement of my house, it is clean out of necessity, If I keep a messy shop I end up tracking stuff into the main living quarters...which I hear about from my better half . About a year ago I bought a Ridgid 1450D shop vac which attaches to the dust ports on my table saw, chop saw and a few other tools I have, it really keeps things clean. It has major suction, very highly rated on Amazon.


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starman345
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Re: 14" Hubble Optics Project new [Re: Pinbout]
      #5576856 - 12/18/12 06:55 AM


Quote:

very clean.




A coat of flat black paint will make them look like a professional made them


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starman345
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Re: 14" Hubble Optics Project new [Re: KenScharf]
      #5576876 - 12/18/12 07:21 AM

Quote:

It's been a while since I last looked at Kriege's book, but you seem to be following it closely.



I do have the book and started out intending to follow it closely but I've drifted away from it in several respects. Reading this and other forums has given me several ideas to incorporate into the build.

Quote:

I'm in the process of making a 7" mirror and will probably make a miniature version of his design. I'm giving some though to making the truss clamp blocks by sand casting aluminum a-la Gingery instead of out of wood (though I'd have to make wooden patterns to make the sand molds!).




Thats interesting about sand casting the truss clamp blocks in aluminum. If you end up doing it I hope you start a thread about it on the forum.


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5626777 - 01/16/13 06:44 PM Attachment (34 downloads)

After a break I"m back at it in the shop. I hope everyone had a good holiday.
I made a cover for the mirror box to protect the mirror, nothing special just 5mm ply with a piece of 1" dowel for a knob


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5626779 - 01/16/13 06:46 PM Attachment (24 downloads)

I got a new Bosch router for Christmas so I routed out the altitude bearings and glued and clamped on the ebony star

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5626784 - 01/16/13 06:47 PM Attachment (27 downloads)

Then the fine touches with a file

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5626791 - 01/16/13 06:51 PM Attachment (26 downloads)

Tonight I set the bearing at 30 degrees to the mirror box and clamped it in place. Tomorrow I"ll drill the holes to anchor both of them.
I came up short of plywood so ordered another sheet that will be in tomorrow, then I can make the ground board and then put it all together. Then the test under the stars...


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sopticals
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5626842 - 01/16/13 07:32 PM

Looking good Brian.

Stephen.(44deg.S.)


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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5627786 - 01/17/13 10:44 AM Attachment (42 downloads)

I installed the bearings this morning and put the telescope together. It balances!!! With nothing in the focuser the ota drifts up just slightly, with my 21E, 13E, and 6.7ES it stays wherever I put it I did the balance calculations based on the weight of the 13E which is less than the 21 but more than the 6.7.
I was hoping to take the scope for a test run this weekend but now I see the forecast calls for cloudy and snow, maybe I"ll wait until next weekend when it is -30


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sopticals
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5628488 - 01/17/13 05:12 PM

Really nice Brian.WOW!!! look at all those great "hogging tools" in the back ground.

Stephen.(44deg.S.)

Edited by sopticals (01/17/13 05:13 PM)


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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5628701 - 01/17/13 07:21 PM

You are showing your real colors Stephen, only a true glass pusher would see weightlifting equipment and think "hogging tools"!!!

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5651905 - 01/30/13 09:41 AM Attachment (27 downloads)

The telescope is finished, except for some varnishing on the rocker box and ground board. I've done some sanding on the ends of the truss poles so they slip into the lower truss connectors easily and also, cut them all exactly the same length so collimation doesn't change from setup to setup. Well, sometimes I need to tweak one of the secondary tilt screws but I think it holds collimation pretty well.
A couple of days ago I took the scope out for its first light and was disappointed, at least at first. My eyepieces all came to focus but I had a hard time bringing the stars to points. I had let the scope sit about 45 minutes outside but apparently that wasn't enough, I came back about an hour later and the difference was like night and day, stars were much sharper. The scope had been in my basement at 70F before taking it outside where it was a cool windy 15F, so maybe it takes more time with that kind of temperature difference. Hubble Optics advertise that these sandwich mirrors cool down really quickly but maybe I was asking too much for that temperature range. The clouds rolled in and ended my session way too early.
Today I played with the mirror a bit, the top post(wood dowel) that holds the retaining clip was rubbing against the mirror so I backed it off and I think that may have helped the images tonight. Glass seems to be really sensitive.
I set the scope up outside about 4 pm and around 7pm I went out and found M42 in my Stellarvue finder then put the Ethos 21mm in the focuser, what a sight, I have never seen M42 like that before, so much detail I didn't realize was there. The 21mm is so wide and the dust lanes were streaming out in all directions. This was really the first time I"d got to use the 21mm, having acquired it a few months ago while the scope was under construction and I had no way to try it. I adjusted the Stellarvue to more precisely line up with the scope and swung around to Jupiter, really nice, put in the Ethos 13mm and just took it all in. My other scope was a 10" and with this 14" there really is a big difference. I can definately see more bands and they seem sharper. I put the Explore Scientific 6.7mm in the focuser to have a closer look but for some reason I couldn't really get the detail the 13 & 21 were showing. I"m not sure why, maybe the seeing wouldn't support the power.
I am noticing the stars away from the center of view are pretty fuzzy, I suppose that is coma and I'll probably have to get a Paracorr, no sense having expensive wide FOV eyepieces unless the whole view is sharp.
I played with the focus, both at zenith and various angles towards the horizon, the stars seem to get harder and harder to focus to points from around 45 degrees down to the horizon. The cell may need to be re-done, changed to a sling, or something else but first I'll need more viewing sessions to make sure what is going on.
All in all I'm very happy with the telescope, a great fun project, frustrating at times but rewarding. I couldn't have done it without all the help I got here on the forum, in this thread and from other forums as well, also, Reiner Vogel's excellent website was great in helping me understand some of the geometry and design concepts. Thanks everyone.


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starman345
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5651914 - 01/30/13 09:44 AM Attachment (28 downloads)

The scope sporting a black shroud. I bought the nylon-lycra material for $18 and a local seamstress put it together for $10.

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PaulEK
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5652358 - 01/30/13 01:41 PM

Looks great!

I've been following your thread, in part because I'm hoping to build a scope around the Hubble 14" sandwich mirror, but I plan to put mine on an EQ mount. It's good to hear that the mirror seems all right. I do plan to have mine sent directly to someone who can test it, and then re-figure it if needed.

I also have a 10" reflector. It has a Hubble mirror that gives fine views, but that didn't happen until after it was re-figured by this same person. He figured it was about 1/3rd wave or worse before re-figuring, and about 1/10th after. The difference in viewing was vast!


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sopticals
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Re: 14" Hubble Optics Project new [Re: PaulEK]
      #5652776 - 01/30/13 05:03 PM

Hi Brian,

What a great result. You will be looking forward to lots of clear night skies.

Best regards
Stephen.(44deg.S.)

Edited by sopticals (01/30/13 05:05 PM)


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Re: 14" Hubble Optics Project new [Re: PaulEK]
      #5655750 - 02/01/13 08:18 AM

Quote:

I've been following your thread, in part because I'm hoping to build a scope around the Hubble 14" sandwich mirror, but I plan to put mine on an EQ mount.




Hi Paul, that sounds like an interesting project, I hope you document it here on CN, I have been kicking around doing something like that.
Having looked through only two telescope mirrors in my life I"m no expert on whether a mirror is a good one or not. It seems good but I am concerned that I couldn't get much detail with the ES 6.7mm while observing Jupiter. More observing sessions are needed for sure.
Was the Hubble Optics 10" a recent purchase or older? Sad a mirror needs figuring right out of the box.


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Re: 14" Hubble Optics Project new [Re: sopticals]
      #5655762 - 02/01/13 08:21 AM

Quote:

Hi Brian,

What a great result. You will be looking forward to lots of clear night skies.

Best regards
Stephen.(44deg.S.)




Thanks Stephen, I appreciate the kind words. I've been reading your epic adventure on glass pushing on another forum, you have inspired me to dust off that 14" piece of glass in my basement.....next project


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PaulEK
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5656335 - 02/01/13 01:08 PM

Brian:

I bought the lens on eBay about 4-5 years ago, if I recall correctly. I'm no expert on optics, either, but it was clear right away that this one had problems. I've read that they sometimes do make great mirrors, but like so many mass-produced items (not just from this company), quality control is a big issue, so they have also made not-so-great ones. It's too bad, and in my opinion, bad business practice. If they could develop a good reputation, based on consistent product quality, it could do nothing but help them grow. Even if they never made fantastic mirrors, but always made okay mirrors, they would be better off. They might be working on this now; mine is fairly old. But they claimed in their ad that it was 1/34th wave, with a Strehl ratio of .996! I knew that was too good to be true. And it's another reason to be concerned.

Still, I don't regret buying it at all. Even after re-figuring, it cost far less than an excellent mirror made by a firm with a better reputation. And it is now an excellent mirror.

My concern with the sandwich mirror is that I read a post somewhere that told of one that could not be re-figured by someone making the attempt, because of the sandwich construction. I don't know if it was that particular mirror that was the problem, the person's re-figuring skills or tools, or a problem inherent in all of them. I need to do more research -- or hope for an answer on this thread!

I still think it's possibly going to be worth the risk, especially since it's probably the only way I'll be able to afford a mirror of this size.


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PaulEK
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Re: 14" Hubble Optics Project new [Re: PaulEK]
      #5656352 - 02/01/13 01:18 PM

Oh! Your other point, about the build I hope to do: It will be a few months before I get started, but I do plan to post about it here. Right now, I'm thinking about a thin plywood skin over plywood rings. I want it to be round, so I can rotate it for eyepiece placement. Here's a source for thin plywood, from 0.4mm to 6mm. I need to find about about weight, since I want it as light as I can make it, while also having a strongly built tube. But for what I'm hoping to do, I think a sheet that is 61" x 61" will work very well. In fact, I don't think there will be any extra bits left.

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starman345
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Re: 14" Hubble Optics Project new [Re: PaulEK]
      #5656839 - 02/01/13 05:42 PM

Quote:

Still, I don't regret buying it at all. Even after re-figuring, it cost far less than an excellent mirror made by a firm with a better reputation. And it is now an excellent mirror.




That crossed my mind too when I bought it.


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Re: 14" Hubble Optics Project new [Re: starman345]
      #5656851 - 02/01/13 05:49 PM

If you haven't already read Albert Highe's book "Engineering, Design and construction of Portable Newtonian Telescopes" you might want to give it a look. He talks a lot about thin plywood, design stiffness and such, how to determine weight, etc, lots of engineering stuff. It might be helpful to you in your project. He also includes a cd in the back cover that includes several Excel spreadsheets for determining balance, bearing sizes, etc. Its a great book!

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PaulEK
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5657176 - 02/01/13 09:32 PM

Thanks, Brian! I've heard of the book, but didn't know it went into those kinds of details: it sounds like it might be just what I need.

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Re: 14" Hubble Optics Project new [Re: PaulEK]
      #5718594 - 03/07/13 02:46 PM

Excellent job, Brian! A type 1 Paracorr will work fine.

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Re: 14" Hubble Optics Project new [Re: star drop]
      #5718642 - 03/07/13 03:10 PM

Thanks Ted, I"m holding off on the Paracorr until I get my mirror back. I sent it to Normand Fullum for testing, he said it was an average mirror but he thought he could improve it so its now being re-figured. Its an f4.5 so I imagine the coma will still be the same but I want to have a look through it first before I cough up the money for a Paracorr.

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Re: 14" Hubble Optics Project new [Re: starman345]
      #5808721 - 04/19/13 01:56 PM

I wanted to update this thread and put the bow on it..so here is what has been going on.
A couple of weeks ago I received my Hubble Optics mirror back from Normand Fullum, his re-figuring has made a major improvement to an already decent mirror. I"ve had it out three times so far and it now comes to focus quickly, there is no need for fiddling with the focuser to find the best spot, it seems to snap to focus which it didn't before. It was well worth the investment for the improvement. Normand was quick to turn my mirror around, answered all my questions and I would certainly do business with him again. He is a class act.
This week I received a Paracorr 2 and must say after using it in one session, it will be residing in the focuser permanently..what a difference. With Ethos eyepeices the stars are tiny points right to the edge, no coma whatsoever that I can detect.
The scope, at 82 total lbs from ground board to top of secondary, is a load to move so I've been planning a platform on wheels so I can just roll it out of my garage without tearing it down and re-assembling each time. The platform also gives me an opportunity to add a little height to the eyepiece position..now at 60.5", with a platform it will be about 64-65" which is more convenient for a person 6'1". Keeping it stable might be a challenge.


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sopticals
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Re: 14" Hubble Optics Project new [Re: starman345]
      #5809357 - 04/19/13 07:28 PM

Hi Brian,

congratulations on the finished work. You will be looking forward to years of observing enjoyment.

Best regards
Stephen.(44deg.S.)

Edited by sopticals (04/19/13 07:29 PM)


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