Really need a complex mirror support?

[azzythehillbilly]

I am in the final stages of completing my DIY 10" GSO mirror based Newt. After starting to build a 9 point whiffle tree and all the problems attendant, I was wondering if the mirror ( 10", F5. BK4, 35mm thick) could be laid over a flat 1" thick fiber plate with three bumps where the 3 point supports should  be.
 
Is it really necessary to have a 9/12 point whiffle support?  Am I just gilding the lily?
 
I want to use my T'scope for visual and occasional photography with a P & S.
 
My own calculations, with a bunch of simplifying assumptions, using my (rather  rusty, I graduated from engineering college in 1970 )  education of ages past, seems to indicate that the max deflection at the edge with a single support in the center is less than .15 wave length at middle of the visible spectrum. But might be wrong.
 
I just want to get this finished so ready to drop some niceties for the sake of progress.

Earlier I had to go through tortuous affair of selecting one of the two diagonals I have. (50mm vs 73mm).  Some empirical testing indicatioed no visible difference.

Perhaps the same with the mirror support.

I do thankfully look forward to some candid advice from those who know better than I do. This my first project ever so I am a bit naive.

Azzythehillbilly

[Moonshane]

three point supports are fine for mirrors up to 12" I feel, especially for visual. my 12" f4 has three point support. if I were making a cell for a 10"-12" scope I'd almost certainly make a 6 point cell. this has two points on a bar on the top of each collimation bolt which should be free enough to tilt, rather than the mirror balancing on the collimation bolts themselves (depending on design of course. In my cell for the above scope, the collimation bolts connect to a disc through which a different set of three plastic/nylon bolts protrude to hold the mirror in place. if you google 'six point mirror cell' and look at images, you'll get the idea.

[skybadger]

In my first 12" I used a 18 point design with pairs of cantilevered triangle supports. For the next one I used a 9 point support. If you can reduce the support impact to the mirror to

negligible easily enough, why wouldnt you?.

Mike

[callump]

For a 10" mirror a 3 point support will be fine.

I favour using silicone to fix the mirror to a backplate, and fixing the backplate to the tube in a way that provides the collimation adjustment.

See the 10" mirror cell in Richard Berry's "How to make a telescope" book.

The scope I am building at the moment is a 12" and the cell will be a 6 point design, but the mirror will still be glued to the rocking supports.

Callum

[Moonshane]

In my first 12" I used a 18 point design with pairs of cantilevered triangle supports. For the next one I used a 9 point support. If you can reduce the support impact to the mirror to

negligible easily enough, why wouldnt you?.

Mike

it's not so much about this but about what is optimum. surprisingly sometimes less support points is optimum and more points is not. off the top of my head I think six points is optimum for a 10" mirror according to some of the online software calculators (based on last time I looked a while ago).

[John]

My 12" F/5.3 Orion Optics dob uses a 3 point support - probably the same design as Shanes 12" F/4. It does the job well, is easy to adjust and the scope holds collimation very well.

My old Meade Lightbridge 12" used a 9 point support but it did not hold collimation too well even when the primary collimation springs had been upgraded. The Meade cell seemed to be made of metal that was a little flimsy to me.

[azzythehillbilly]

What I wanted to determine was whether it is worth the effort to go overboard and have a 6/9/12 or some such point support.   I , like everyone else has only so much time  to devote  to a single hobby. I have several others.  

I just want to be reasonable.  

I think  I have two questions.

1.  What kind of mirror support does the Jhumell 10 inch have?  Can I have some pictures? Might be just the thing to copy. ( A bit of reverse plagiarism might be OK)

2. Which is a better 3 point support structure, easy to align and will hold a colimation decently?

Thanks for all the help guys.  The replies have helped me steer in the correct direction.