Flexed mirrors Bino.

[CharlesM]

I'm in the process of building a 12" f6 bino using two flexed mirrors.
Has anyone used Alan Adlers Flex program to make a flexed mirror?
I did use it some years ago to sort out an 8" f3.7 under corrected mirror but with an excellent surface we didnt want to harm.
It flexed to produce a superb image.


I want to make a pair of 12" f6 flexed mirrors for my binoscope with curved backs and I'm hoping I can get some answers for the following questions regarding the programs output.

1, If you input 0 to find best back radius the output screen shows back radius, spot, and a column labled W. What does the W stand for?

2, what exactly does Beta1=.01 and Beta2=.92 mean on the graph screen?

3, In Alans notes he states that if a curved back is used the the outer pusher cushion is better to be narrower and the puller obviously larger.
Anyone know what would be a reasonable dimension to use?
I'm considering 5mm perimeter cushion and correspondingly larger dia puller.

I ran flex with curved back and flat back and the dimensions for puller and pusher are identical so it doesnt reflect Alans points.

[Rod]

Hi Charles

I’m not sure that anyone on this forum has actually tried flexing a mirror. The topic has come up but I don’t recall anyone reporting on actually trying it. There is this thread currently on Cloudy Nights:

https://www.cloudynights.com/topic/7...-a-paraboloid/

You might get some answers there.

BTW I saw your thread in Hobby Machinist linked in the other thread. Very Impressive! I noticed you have built a grinding/polishing machine. Any reason you don’t want to parabolise the mirrors? At F6 it shouldn’t be too difficult.

I’ll be following your progress. I’ve only looked through a big binocular once and the view still haunts me. It was a 10 inch and the 3D image was spectacular.

Rod

[mura_gadi (Steve)]

Hello,

I posted about flexing mirrors a few months ago, I got one response from an ISS member who had tried the flex mirror system. A quick search might show up the thread and you could try the member directly.

Think I used "Kelley and Alder" for the flex mirror system, mostly read the Sky and Telescope article and only a quick look at flex.


MG
Only bit from the help file for "W":


WHILE IN THE GRAPHIC SCREEN, TRY THE "W" OPTION TO SEE THE
EFFECT OF CHANGING THE FLEX TENSION. FOR MODERATE SPEED
MIRRORS, A CHANGE OF TEN PERCENT OR MORE FROM OPTIMUM IS
VISUALY ACCEPTABLE. FOCUS WOULD SHIFT SLIGHTLY, BUT THE
PROGRAM AUTOMATICALLY ANALYZES THE IMAGE AT BEST FOCUS.

[CharlesM]

I will keep you updated as I go.
This is a very experimental project.
The glass is only 19mm thick.
I will be grinding the back to almost the same profile as the front so the final mirror will be very thin, around 9.5mm
I will be using steel dumps epoxied to the pre generated tools for all the grinding.
I have to grind the mirrors circular first as they are around 1mm out of perfect circle.
The curve generation will be performed by a hanging pendulum grinder to get both mirrors to the same roc.
The mirrors will be set in dental stone so they dont rock on the back curve.
I may go with submerged grinding to get the best use of all the grit.
I have used all these methods in the past and they worked very well but this will be the first time they will all be used on the same mirrors in the hope I get two matched focal lengths.
Here is the flex output for what I hope to accomplish.

[mura_gadi (Steve)]

Good luck with the project, be interesting to hear about the pitfalls. The Sky and Telescope article suggested 1:10 as the best ratio. You might find controlling the flex on such a thin/fast mirror very challenging. I think they were quoting F8's at 1:6.

Look forward to future posts.

[CharlesM]

Another quandry I have is do I just rely upon using the standard collimation bolts to make tiny adjustment to get image fusion?
or
use a sliding rig so the mirrors can move a tiny amount in the xx and yy plane?
or
use both methods?
If I rely upon the standard collimation method and it is insufficient then maybe both methods would solve it.
but if the x y plane movement is not required then that a lot of fabrication I will not need to do.
But if it is required and I havnt engineered it in its a pain to add it in after everything else is done.

[CharlesM]

It can still be downloaded from sky and telescope but Alan has also given permission for it to be stored on here as well.
https://skyandtelescope.org/astronom...sky-telescope/

[mura_gadi (Steve)]

Hello,

I am trying familiarise myself with a program called "GUI Plop", which deals with mirror cell design.

I saw there was a tick box for "Warp Sphere to Parabola" in the mirror cell design style. Might be worthwhile exploring the program and possibly any community help as well in regards to the mirror cell design for your Kelly-Alder bino's.