The Giant Binocular

[rwm]

I don't doubt you Charles but this seems dauntingly complex! Will it work???

 

[savarin]

It wont be easy Robert.
Some of the challenges:-
The method of pulling the spherical mirror into a parabolic optic works, I have successfully done this with an 8" f3.7? optic so I dont have a worry about that.
Aligning the two tubes optically is difficult, I have added various methods to help adjust for this, will it be enough? I am hoping it will be.
Polishing a sphere is relatively easier than polishing a parabola and easier to test so this shouldnt give too many problems.
I have chosen a focal ratio of f6 which will give me more lee way in optical alignment.
Getting both mirrors to the exact same RoC is a difficult one, but, the eyes can adjust to small differences on focal length
The eyes can handle small differences in alignment but it will produce really bad headaches if too far out of collimation. I have adjustments in place to sort this.
I think the biggest problem will be the many knock on effects of all the adjustment parameters, I'm hoping the laser will be my friend in this.
So, will it work? My fingers are crossed.

 

[rwm]

I am curious; once you pull it into a parabola, will it remain stable? Will you need to adjust periodically? Would it be worth the effort to just grind the parabola?
R

 

[FOMOGO]

The main problem I see with these binoculars, is finding the right lanyard to hold them around your neck. Cheers, Mike

 

[savarin]

I am curious; once you pull it into a parabola, will it remain stable? Will you need to adjust periodically? Would it be worth the effort to just grind the parabola?
R

Figuring the parabola is fraught with problems, I chose this method after doing the f3.7? and watching it change from a good sphere into an awesome parabola. I also went with f6 to make the job even easier.
The f3.7? wandered in tension for the first couple of weeks but then steadied down to a tiny tweak every now and again. It remained remarkably stable after a very short while.

 

[savarin]

heres a quick videa of the grinder in action using 80 grit. I went back to 80 as the grinding process is going so slow.

The strange pale blotches on the disk are where I spritzed the water on.
After 4 hours I still havnt got to the centre of the disk but it is getting there.

only another 6/100s of a mm to go or 0.002362198"
My mind appears to be deteriorating fast, I kept reading this number as 0.069mm instead of what it really is 0.69mm.
I have to go back and do the math again and hope to hell I havnt totally stuffed up

 

[savarin]

Oops, made one mistake.
The 0.69mm is fine for the front concave surface of the mirrors but the back should be 0.70 so need to move the tool in a tad to get back to the 0.70mm

 

[rwm]

Seem like you may need another significant figure if you are trying to get to 0.70? How do you know if that is 0.690 or 0.699? What is the error tolerance?

 

[savarin]

It should be 0.703 mm but I have nothing to measure that precise so its a bit of a guess, but as the pullers will be glued to foam rubber 12mm thick I believe a couple of thou of a mm will not be a problem. (He states with fingers well and truly crossed)
With the mirrors I can accurately measure their focal length and polish to the correct figure.

 

[rwm]

That makes sense. I can't wait to see this process!