The 22" mapstar mirror

[faulksy]

good luck damian

[Physopto]

Hi Damian,

Good luck, I expect you will be watching that edge very carefully this time.

I'm sure you will get it.

All the best.

Derek

[barkis]

I love that velvety feel of the very finely ground surface, soon to be completely polished and figured.

 You can foresee, and sense the beautiful and highly reflective 

and precision worked surface straining at the leash, ready to nestle down in the cell, and awaiting 

collection of the Billions of ancient photons that will soothe away all the left over anguish in your mind from

the effort expended giving birth to this big baby.

Now Damian, with that load of tripe out of the way, it's onward and upward in the real world  me lad.

This time, success is assured, but take nowt for granted, there is an abundance of work and thought left

to negotiate. I have the utmost confidence in your ability to write the final chapter of this very interesting

log book.

Go to it matey, I'm going to watch from the Gallery as you take that longish, triumphant walk to victory.

:icon_salut:  .

Ron.

[Mark62]

Third time lucky. Good luck [emoji2]

Mark

[mapstar]

Cheers guys

I have finished today by Re cutting the lap channels and it's now sat on the mirror atop grease proof paper.

The lap will need to be pressed with just cerium on the mirror to take the full profile.

I am still in two minds what to do on the polishing front but will decide in the next couple of days.

As Ron quite rightly says the velvety surface is nice to see, I will probably give it another hour or two with the 600 aluminium oxide but at present it is scratch free so I need to be extra careful putting the tool back on.

I may get a bit of time on it tomorrow

Damian

[RLWP]

Imitate the action of the tiger, stiffen the sinews, summon up the blood,

Richard

[Uplooker]

Get stuck in big man! I am really hoping and yet confident that this bit of success is the motivation and encouragement that you have been needing for quite some time. I sense a renewed vigor within you Damian, keep at it. I think you have been bitten too many times to rush in, take it gently and you will quickly forget the grief of past times

[Soupy]

Great effort buddy, and good to speak to you earlier you certainly sound like you have a renewed steel in your mind to defeat this beast of a mirror and bring it back under your control... You CAN tame it (sorry going all Ron there for a minute)!

However it is great to sense that your determination has come back with a vengeance though Damian and we are all willing you on. Good luck mate.

[barkis]

Imitate the action of the tiger, stiffen the sinews, summon up the blood,

Richard

Ah!, the Henry V.  Shakespeare quote. Should do the trick  .

[RLWP]

Ah!, the Henry V.  Shakespeare quote. Should do the trick  .

Well, I'm sure we are all hoping for the moment that Damian can say:

And gentlemen in England now a-bed shall think themselves accursed they were not here

Sounds about right for a successful first-light test of a hand made mirror

Richard

[mapstar]

Hi all

This morning I finished the fine grinding with another hour of 600 grit alu oxide.

It now has the lap back ontop pressing but looked OK when I'd taken it off

More later

Damian

[nicks90]

Do you have any testing piccies to show the sphere in all its glory?

[mapstar]

Do you have any testing piccies to show the sphere in all its glory?

Hi Nick

The mirror needs to be polished first before any testing takes place.

A sphere is the classic starting point to working the shape to a parabola. This will take quite await of time for a mirror of this size and focal length.

[barkis]

I used to spray the fine ground mirror with water after setting it up on

the test cradle, and check the radius of curvature length, and thereby /2 it's focal length.

A reasonable estimate could be gained, but also moving the knife edge back an forth to intercept the reflected  light beam

could give a reasonable indication of it's spherical condition.

The illuminated mirror would darken alost  instantly as the knife cut into the light source.

Not a sure fire result, but any drastic event such as astigmatism might be apparent.

It would be extremely unlikely, but not  altogether impossible.

A rare occurrence after fine grinding though.

[mapstar]

I used to spray the fine ground mirror with water after setting it up on

the test cradle, and check the radius of curvature length, and thereby /2 it's focal length.

A reasonable estimate could be gained, but also moving the knife edge back an forth to intercept the reflected light beam

could give a reasonable indication of it's spherical condition.

The illuminated mirror would darken alost instantly as the knife cut into the light source.

Not a sure fire result, but any drastic event such as astigmatism might be apparent.

It would be extremely unlikely, but not altogether impossible.

A rare occurrence after fine grinding though.

John mentioned the reflection test with fine misted mirror but I never tried it.

I instead went for 3 hours of polishing then test.

I can't remember where I read it but you can also shine a light source at the mirror whilst moving it side to side and the reflection should reverse around the focal point? Think I got that right but I do stand correction.

I must invest some time in making a proper foucault tester as I will then have two test methods to go on.

I will eventually call on Johns good nature and expertise to test it on his auto collimation bench to make sure it is figured correctly.

Damian

[wookie1965]

Looking good im always checking on your progress will be great when you finish it, keep up the posts its very interesting.

[mapstar]

Looking good im always checking on your progress will be great when you finish it, keep up the posts its very interesting.

Cheers Paul

[Mrbloke]

Fascinating read throughout! You sir, have the patience of a saint.  I think I would get about 2 hours in and then think - perhaps not...

[mapstar]

Fascinating read throughout! You sir, have the patience of a saint. I think I would get about 2 hours in and then think - perhaps not...

Hi and thanks for reading the thread and for the compliment.

It has been and still is a labour of love which one day will be complete and that's what keeps you going.

Damian

Edited June 27, 2015 by mapstar

[RAC]

What's the depth of the mirror currently?

[mapstar]

What's the depth of the mirror currently?

Hi Raymond.

I have not measured the depth of the mirror but whilst testing at Johns we worked out the the focal length is going to end up around F3.5 which is a little shorter than what I set out for. As the scope is yet to be built I have not made any calculations on the final height of the eye piece.

Damian 

[barkis]

John mentioned the reflection test with fine misted mirror but I never tried it.

I instead went for 3 hours of polishing then test.

I can't remember where I read it but you can also shine a light source at the mirror whilst moving it side to side and the reflection should reverse around the focal point? Think I got that right but I do stand correction.

I must invest some time in making a proper foucault tester as I will then have two test methods to go on.

I will eventually call on Johns good nature and expertise to test it on his auto collimation bench to make sure it is figured correctly.

Damian

Yes that is also a useful guide Damian.

I used to do the small torch trick, starting close to the mirror and walking backward  until moving the light up and down reverse direction when passed the ROC Point.

Walking in the dark, and trying to keep the light on the mirror whilst in a stooped position gave me a hell of a backache at times. I always chided myself for making the test stand too low down,

But it had to coincide with the height of my Foucault Tester  table  :grin:.

[mapstar]

Today's efforts have been nothing to do with the primary mirror.

I have been planning the scope build and what it will be like so gathering my thoughts.

With quite a few of the bits already made I have made a start.I have gathered together all the bits and cut the spider vanes in anticipation of assembly.

All that will be in a different thread so will be on its way later in the year.

Also I will make an update on the mirror by next week hopefully. The lap is pressing nicely in the warm temperatures

Damian

[Soupy]

Oh, that sounds exciting Damian! Look forward to the update and the new build thread.

[estwing]

Have you a time scale for the scope?