Binocular telescope plans

[rmcpb (Rob)]

After looking through the 12" binoculars at the South Pacific Star Party I am considering making a set, they are simply brilliant.

Anyone know of any plans or directions for making these?

Thanx

[Omaroo (Chris Malikoff)]

Rob - I took about 100 photos from all sorts of angles (including internal) of that scope before I left. I'm going to be adding the dimensions I need measured to those photos and will be sending them on to Paul and Mark so that they can elaborate. I'm starting to place orders for helical spiders, truss mounts, secondary holders, etc, etc already for my set. I have also already placed an order on Mark for two of his 12" f/5 mirrors, as per Paul's set.

I've also recently bought "The Dobsonian Telescope - A practical manual for building large aperture telescopes" by Dave Kriege and Richard Berry to get my head around the construction techniques. Only problem is that it starts off talking about 14" as the smallest they cover, but a good text nonetheless.

If you plan to go ahead, maybe we can both grab some ideas from Mark and Paul - and I've already had a good think about using two spare RA steppers to electronically move the mirrors to achieve coaxial alignment.

Cheers
Chris

[rmcpb (Rob)]

Chris,

The coaxial alignment of the mirrors is the bit I have trouble with. If you move the mirror as per the two knobs under the focusers why doesn't it throw out the collimation? I must be missing something pretty fundamental here.

Cheers

[Satchmo]

Hi Rob,

Glad to hear you are inspired by Pauls bino- creation.

What you missed was not fundamental problem , just very crafty solution.

Co-collimation refers to the two optical trains being parallel, hence merged images.

Each mirror sits on two point edge support bolts at 90 degree angle. Winding the bolts allows you to translate each mirror in horizontal / vertical plane and the normal 9 point cell mirror sits on allow usual tilt adjustment. Each mirror flotation sits on a hinged plate with long handle attached for adjustment from the eyepiece.

On the initial night of use, an iterative process is undertaken whereby, after perfectly collimating one side, the images are co-collimated ( merged ) , and then checked for individual true optical 'collimation'. By shifting one or both primary in XY translation plane with the edge support bolts, and then re-tilting the secondaries as need, you are in effect adjusting the parallelism of the two optical axis.

Once you have acheived good co-collimation, with both sides also being in good collimation through the iterative adjustment of the primaries, this adjustment is never needed again. The routinely small tweaks needed then after every setup, or with high power eyepieces, are done with tilting the primaries by the two hinged plates. We also rely on a really good truss system that has great repeatability, for tha I heartlily recommend the Moonlite ball and socket truss connectors. The detection and removal of relative `field-rotation' between the two views which is actually a far more distressing than mis -cocollimation can be subject for another day.

Yes, technically there may be a slight loss of collimation , through this practise of using primary tilt for the final merge. In reality the shift is needed is usually so small, as not to cause any noticeable loss in resolution. The views are stunning. I had my best telescopic views of Jupiter ever very late at night at SPSP. The brain seems to co-add the fleeting detail seen not necessarily concurrently in each eye to form a solid image with all the detail intact. Its almost like flicking a switch...when there is enough data to form a solid image Jupiter seems to go from a blur to hubble like view, and not much in between.

No binoviewer seems to give this effect. Remarkeably body heat just doesn't seem to be the problem that people suggest for reasons I think again due to distortions being different in each eye at any moment. These things were built for deep sky anyway. The contrast in dark nebulae is stunning. They showed the Horsehead at Lostock without a filter, and everything including colours of the stars and apparent eyepiece field is enhanced.

Mark

[rmcpb (Rob)]

Thanks for the info Mark, I think I will have to read that a few times to get my head around it. You are right about the views, seeing Omega Centaurus as a 3D ball was mind blowing!!

Chris,

I also posted this question on CN and have had some more feedback. Have a look if you are interested http://www.cloudynights.com/ubbthrea.../1#Post1566955

[Omaroo (Chris Malikoff)]

Cheers fellas - and thanks for posting your text Mark. It certainly explains itself well.

Rob - I'll have a look at the CN post.

Cheers
Chris

[Omaroo (Chris Malikoff)]

Rob - If you go to my personal website at the following location:

http://www.omaroo.net/index.php?set_...view_album.php

You will see 29 shots I took of its mechanics. These will give you a good idea of how it works.

Cheers
Chris