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Equipment Discussions >> ATM, Optics and DIY Forum

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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: astrobeast1]
      #5651609 - 01/30/13 04:41 AM

Quote:

keep us posted --with pics too



Yeah, good point - I'm pretty slack when it comes to taking pictures. Will do.

On the subject of unsuitable mat substitutes, I've also considered J-cloths, net curtain and landscaping fabric (porous membrane). I think I should stick to chopped strand mat, to be honest.

I've got the external ring removed from that first tube - bit of a mess still but some rasping and sanding should do it. Pins pushed back out with the aid of a small punch and a screw tip. It was the smallest tube (200mm) and held up well to being rough handled. With several kilos and the point loading of the trusses, I'm still going to go with the second mat/resin coat, plus meaty wedges for the threaded inserts.


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5651638 - 01/30/13 06:16 AM Attachment (36 downloads)

Some photos...

A few notes:
- the struts are not the correct length
- I've got both tubes the wrong way round - bevel on the baffles should point the other way
- wedges on the outside of the middle tube will be double thickness
- further wedges will be positioned on the inside of the bottom and top tubes
- tabs will extend further onto each tube, so positioning the threaded insert well within the 'meat' of the wedges
- the tube in the last picture (the one requiring cleanup) has the "matt" spray paint inside, the others have blackboard paint. It's a bit shiny so I'll repaint it.

Three of eight struts roughly located between the middle and bottom tubes


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5651641 - 01/30/13 06:17 AM Attachment (20 downloads)

Close-up of attachment points on the middle tube

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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5651643 - 01/30/13 06:18 AM Attachment (13 downloads)

Close-up of attachment points on the bottom (or top) tube

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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5651646 - 01/30/13 06:18 AM Attachment (27 downloads)

External ring removed from one of the bottom tubes - showing the clean-up required

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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress [Re: furrysocks]
      #5732937 - 03/14/13 08:29 PM

I'm back on it! I now have a Stellafane primary mirror mount in progress and a star party to go to in about 3 or 4 weeks time.

Watch this space... (for a single dobs, no binoscope yet)


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5736695 - 03/16/13 05:24 PM

It turns out the two mirrors are not a pair. I have removed one mirror from the cell in which it came and have washed them both.

Mirror 1
- 216.5mm dia
- 40mm thick
- FL 1620mm
- 3321g
- ~2.26 g/cm^3
- clear or perhaps slightly yellow in colour
- surface fair (several pinholes, few small scuffs, one light scratch)
- figure unknown
- hand scribed "C14A F.L. 1620mm (83.6 in) Made in Endland"

Mirror 2
- 216mm dia
- 24mm thick
- FL 1635mm
- 2154g
- ~2.5 g/cm^3
- definitely green in colour
- surface good (few pinholes, small scuff near edge)
- figure unknown
- no markings

With 15mm difference in focal length, I don't know if I should bother to put all the effort in to pursue the idea of building a binoscope.

I do however have to decide which mirror I will use in the first complete OTA. The weight in particular will affect the proportions of the double truss arrangement.

Any comments gratefully received.


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m. allan noah
professor emeritus


Reged: 08/14/09

Loc: Virginia, USA
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5736946 - 03/16/13 07:13 PM

That's less than 1% difference in focal length. You would never notice it at the eyepiece.

allan


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Chriske
Kijkerbouw Urania
*****

Reged: 08/15/04

Loc: Boechout, Belgium
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: m. allan noah]
      #5738008 - 03/17/13 04:33 AM

Quote:

That's less than 1% difference in focal length. You would never notice it at the eyepiece.

allan




Correct...! Even using high magnifications.
Only using extreme magnifications you'll notice some smaller defect. Not everyone will see it, most people don't.
Go for the bino...! Once you'll made and use it, you'll never want to observe using a regular scope again.
Busy making myself my fourth bino(20") Project temp. on hold.


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: Chriske]
      #5738020 - 03/17/13 04:48 AM Attachment (14 downloads)

Allan/Chris - thanks guys. Perhaps binoscope is still on the cards then.

(Attached photo - don't know why it didn't upload first time)

Edited by furrysocks (03/17/13 06:45 AM)


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5739367 - 03/17/13 06:41 PM Attachment (14 downloads)

Main achievement this evening was to re-glass the center tube and attach the truss supports.

[Edit]
The significance of this is the fact that I had previously been intending to put external rings on each of the three tubes, to which I could attach the trusses. Now, the top and bottom tubes have the trusses attached directly, with the middle tube attachment points either side of the points of these little triangles. (In fact, there will be one ring at the top end of this middle tube to which the top trusses attach and that ring will bolt onto four of these triangles, to let me split the whole scope in two.)

Thanks to astrobeast for the chat leading to the decision to ditch the external rings - it took some figuring out what I was going to do, but I think this now looks quite nice, provided it doesn't all fall apart on me at some point!

Edited by furrysocks (03/17/13 07:21 PM)


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Chriske
Kijkerbouw Urania
*****

Reged: 08/15/04

Loc: Boechout, Belgium
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5740006 - 03/18/13 02:30 AM

Hi,

Beside the long list of advantages observing with two eyes there is that very peculiar and funny fact about bino viewing.
While observing with a large bino at night you'll get a 3D effect. Of course that's not a real 3D effect.
Because you observe through 2 different 'air-channels' you'll get two slightly different information-streams coming in. These differences in information are caused by the different turbulences in both scopes not coming in synchronously.
Very nice effect. (not visible in small hand-held bino's)

Needles to say, this effect is not visible using a binoviewer in a single scope of course


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: Chriske]
      #5741783 - 03/18/13 09:17 PM

Looking forward to the bino-effect you describe... eventually.

In the meantime, I spent another 4 hours on the first OTA build tonight - getting there. Estimate another 20 hours or so until first light! It's a race against Jupiter...


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jgibson1@emich
professor emeritus
*****

Reged: 06/11/06

Loc: Tucson, AZ
Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5742075 - 03/18/13 11:59 PM

Quote:

It's a race against Jupiter...




Good luck sir! I just snagged an amazing view of Jupiter with my new homebrew 8" tonight. I wish you better luck with the clouds than I am having. Day two of having a new scope and CLOUDS..... Again!!!

Clear Skies,
Jason


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: jgibson1@emich]
      #5742205 - 03/19/13 02:33 AM Attachment (13 downloads)

You must be chuffed, though! What EP/mag did you use?

We've had snow overnight and more forecast all week so it'll be rather cold out in the garage. I'll post a pic of my curing cabinet - I couldn't have done this build at this time of year without it! Early on, I tried - resin took about 4 days to cure to non-tacky. At 30deg, it's about an hour then a few more to harden completely.

Edited by furrysocks (03/19/13 04:37 AM)


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5742268 - 03/19/13 03:50 AM Attachment (13 downloads)

Photo of a Stellafane curved vane and secondary mount.

Edited by furrysocks (03/19/13 03:51 AM)


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5746256 - 03/20/13 08:53 PM Attachment (10 downloads)

Somewhere around 6 feet long...

Edited by furrysocks (03/20/13 08:54 PM)


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5748301 - 03/21/13 06:58 PM Attachment (12 downloads)

First light!!!

I labored over the maths to get the focal length folded to within the range of the focuser, measured my EPs, left some spare room both in and out. I then drilled four struts to connect the top and bottom tubes together using 4 of the 8 threaded inserts on each.

With the front end sitting on a folding workbench and the back end on top of 4 spare van tyres, I aimed for the floodlights of a farm a mile or so away. Dropping down from a 30mm to an 8mm EP (both Vixen NPLs), I got a cracking view of both elements in the light as well as the branches of a tree swaying in front of it.

Very happy with where the focuser sat with both EPs - unless I've got it wrong, I should have the focuser further in for astro over terrestrial.

Next job, cut and drill 16 trusses and put this thing together. It was about as rigid as a banana, tonight.

Happy days!

Edited by furrysocks (03/21/13 06:58 PM)


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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5750458 - 03/22/13 07:41 PM Attachment (9 downloads)

I have completed the first OTA. Phew!

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furrysocks
member


Reged: 01/24/13

Re: DIY 8.5" f/7.6 binoscope - in progress new [Re: furrysocks]
      #5750464 - 03/22/13 07:44 PM

Still a bit of matt black to do inside (inside of the trusses, spider, focuser, some bits of wood, etc...)

I'm not sure if I like it or not.


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