Plans for reflector with 2 primaries

[Paddy]

Seeing the post about incredibly low cost GSO 12" reflectors has raised a few questions about how I might increase my viewing power. I have been contemplating building a scope with a 16-18" primary, but now I wonder if its possible to build a scope with 2x12" primaries. Has anyone done it? Would it need 2 secondaries? Can it be done with one eyepiece? Would it increase the resolving power compared to one 12" primary, or only light collected?

Any thoughts much appreciated

[programmer]

I couldn't help Googling this.. seems there's a US patent taken out on a reflector with two primaries (and two secondaries, and tertiaries!). :)

http://www.patentstorm.us/patents/5430577.html
(http://www.patentstorm.us/patents/5430577.html)

[Satchmo]

I think here you are suggesting a multi mirror telescope? I don't think it is possible with ameteur technology.

Why not use one 12" mirror for each eye and enjoy the 40% image contrast increase that a true binocular gives.

[Paddy]

I was hoping to save the cost of duplicating eyepieces, but I suppose that if I was able to double my light gathering with a second scope for $600 as opposed to the cost of a 16-18" mirror, the cost of a few eps would be easily covered.

Hmmmm.

[Stevo69]

So, how would this work?

1: Two primary mirrors converging onto 1 secondary?, or...

2: Two primary mirrors reflecting onto two secondaries, then converging into one focuser?

I am curious.

hoo roo

[janoskiss]

It would not work with two ordinary parabolic mirrors. You cannot satisfactorily merge the two separate lightpaths without losing at least half the light in the process.

[prova]

http://www.gmto.org/

[PhilW]

This approach is beyond the reach of amateur builders, as previously noted.

The closest we can get is the binewt, as well documented here:

http://www.binoscope.co.nz/

[AstralTraveller]

I'm interested in the phrase 'a true binocular'. Is this meant to imply that a binoviewer doesn't give a 40% increase in image contrast? I have a WO binoviewer and I'm sure it increases image contrast, but I wouldn't like to estimate by how much.

[Orion]

Why stop at two!
Put three together, why should the professionals have all the fun.
It would be a challenge to design a mirror cell to accommodate three mirrors not to mention the telescope build.

[Ian Robinson]

You need a special figure on each mirror I think to do a Magellan thing.

Why can't you direct the light from 2 or more ordinary primaries ? more area means more light.

It's just an engineering problem and so long as the mirrors are matched .... focal length .... why not ??

George Levanis .... here's a good experiment for you.... : :) :

[Orion]

I am going to talk to George about this one, you never know there might be a way of achieving this.

[Stevo69]

I understand all the replies concerning the technical impossibilities of this idea, but really, who cares ;) Why no imagine one of these in your backyard??? Nothing says we cannot have fantasize?

[Paddy]

I'm very grateful for all of these responses and the link to the binewt site. Very interesting and has me imagining! I wonder how to site the focuser tubes on a binewt so that they can be practically used. The photos on Dave's binewt site seem to indicate that the eps are under the scope. This would be fine for higher objects, but with a shorter focal length scope say 1500 mm it would make viewing lower objects quite difficult. Are there other arrangements? Has anyone used one of these and if so, how was the accessibility of the eps?

[AstralTraveller]

Paddy,

I haven't seen the scopes you mention. However I did see first light with Mark Sutching's first binoscope, of 15-20cm aperture per mirror (I've forgotten which) back in '87,. Stunning! Anyway the eyepieces were 'under' the scope but also looking 'backwards' (ie the observer was looking 180 degrees away from the object being viewed). This is obviously a problem for objects near the zenith, but we managed to find enough objects in the 45-60degree elevation range to do a dusk to dawn session. I remember that night with great fondness even 20 years later.

[Ian Robinson]

JMI does a strange looking contraction (big newtonian based binonewts), check out their website. http://images.netshops.com/mgen/digimarc.ms?img=master:JSMM039.jpg&h=300&w=300 (http://javascript<b></b>:popUp('/cart/iso.cfm?detail=extralarge&sku=JSMM039&img=master',650,600,1))
http://www.telescopes.com/binoculars/astronomy-binoculars/jimsmobilejmirb145reversebinoculart elescope.cfm
I expect unless you use fancy relay lenses or use much bigger secondarys than usual , that vigetting and back focus with binonewts would be a big issue.

Those are star diagonals (the tertiaries) , if at zenith .... just rotate them to a comfy angle.
They have
Eyepiece Spacing: Variable from 2" to 3.25" .... surely they could have made the secondary cage rotateable at that price !!!???!!!! peoples eye spacing is constant last time I looked in the mirror.

[Satchmo]

Yes thats what I intended to say. I spent a fair bit of time with a 12" binocular in the last year and comparing to a beamsplitter binoveiwer , I don't see nearly as much contrast improvement. I think its to do with the brain needing two completely differnt optical signals.

[Satchmo]

Glad to hear the night made such an impression :) The binoculars were 8" F8 and got 10 years of service.

Actually the zenith is quite comfortable , looking down into the eypieces, but down low they are more difficult. We may not have had a step ladder that night...

[Satchmo]

No its not an issue at all. You generally use diagonal one size larger than normal. By using compact star diagonals there is no extra vignetting. My upcoming 14" F4.6 binos are using 3.1" diagonals which are only about a 22% obstruction.

The `reverse' binocular Newt design ( as JMI have called it) is by far the most common and simplist to make. Anybody wanting to make a success of the project would be wise to copy successful examples.

William Herschel was the first to build a Newtonian binocular with 6" mirrors of his standard F13 focal ratio.

[PhilW]

I used 2" diagonals on my 10" F/5 bino, for a 20% obstruction. You can work it out using binewt.jar, which Mark previously pointed me towards:

http://www.astrosurf.com/eroyer/BinewtDesigner/Binewt.htm

I've had the same experiences with binoviewers vs true binoscopes. My guess is that because binoviewers produce two identical images, your neural binocular summation mechanism is not fully engaged.

The adjustable observing chair from Bintel is a perfect match with this scope, at least up to about 70 degrees. Then you actually have to get up on your feet to look down the eyepieces. :doh:

[Roger Davis]

This is akin to an Herschellian telescope.
You cannot use two parabolic mirrors to produce a single image as the meridional (imaging) planes are not coincident. You have to produce two off-axis parabaloids to make both meridional planes coincident.
If you are making a mirror and you take a big chip out of one side, save it and make an unobstructed Herschellian!

[Stevo69]

Without going too off track (an apologies if this appears elsewhere in IIS), but what about this pair of bino viewers. Your next project Mark?

http://www.astro.virginia.edu/class/oconnell/LBT/

[GrahamL]

:thumbsup:gotta love the 80's mark kombis and lots of hair .

[Paddy]

Thanks for all the input and some great links. Using the 2 diagonals as opposed to a binoviewer looks very interesting. Don't mind the idea of the 8.4 metre primaries, but the total scope might be a little tricky to get through the shed door on a trolley.

[Satchmo]

Dave Moorehouse's 8" F6 bino was a simple build with 2X GSO 8" F6 Mirrors...

http://www.binoscope.co.nz/babybino.htm

[South Poll]

Why stop at 2 primary mirrors ??????


...or how about these for binos ! ??....


I know, these pics will have been seen before.....but ya can never get enough of stuff this cool :D

[Ian Robinson]

I bags the left one ....:thumbsup: (the missile tracking double telescope thing).