DIY 8.5" f/7.6 binoscope - in progress
Posted 14 March 2013 - 07:29 PM
Watch this space... (for a single dobs, no binoscope yet)
Posted 16 March 2013 - 04:24 PM
- 216.5mm dia
- 40mm thick
- FL 1620mm
- ~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"
- 216mm dia
- 24mm thick
- FL 1635mm
- ~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.
Posted 16 March 2013 - 06:13 PM
Posted 17 March 2013 - 03:33 AM
That's less than 1% difference in focal length. You would never notice it at the eyepiece.
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.
Posted 17 March 2013 - 03:48 AM
(Attached photo - don't know why it didn't upload first time)
Posted 17 March 2013 - 05:41 PM
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!
Posted 18 March 2013 - 01:30 AM
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
Posted 18 March 2013 - 08:17 PM
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...
Posted 18 March 2013 - 10:59 PM
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!!!
Posted 19 March 2013 - 01:33 AM
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.
Posted 19 March 2013 - 02:50 AM
Posted 21 March 2013 - 05:58 PM
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.
Posted 22 March 2013 - 06:44 PM
I'm not sure if I like it or not.
Posted 22 March 2013 - 07:56 PM
Earlier tonight, when I'd gone round double-tightening all of the truss bolts, I lifted it up and stood it on end, stood back and my first thought to myself was "@£$%, it's ugly!!". I'm slowly coming round, but it's not quite a thing of beauty to me yet. There are better designs out there - this one's pretty unique!
I just hope the views will make all the effort worthwhile. I'm certainly not thinking binoscope this year.
Posted 26 March 2013 - 06:50 PM
Patchy cloud, full moon, some LP - not a particularly dark sky at all. No light shroud on the trusses, unpainted stainless steel spider, white focuser barrel, etc... Used 30mm and 8mm Vixen NPLs.
I blinded myself looking at the full moon, got my first view of The Trapezium, easily observed two bands on Jupiter, even through cloud, and discovered just how quickly things move out of field at >200x.
Both axis bearings are way too stiff to move the scope comfortably - some work is required there.
Optically, I haven't a clue. I'd previously got the secondary positioned well and then laser collimated once I was outside - I admit I was in a hurry though. There are lots of bits and pieces in there that I'm sure will cause diffraction. The 8mm (200x) was perhaps pushing it but I'll learn.
Taking it to darker skies this weekend, forecast is favorable.
The thing's a beast though! Seeing about some decals, too.