Second Annual Mid-Atlantic Mirror Making Seminar
Recap

Attendee Comments

Ed Witkowski
More from Ed Witkowski
John Hutto
Aart Olsen
Jack Glasheen

From the ATM List:
Ed Witkowski .... subject: ATM Delmarva Mirror madness
Greetings Atmers,
This past weekend I attended the Delmarva Stargazers 2nd Annual Mirror Making Seminar or was it "Grinding Mania!!" or should it have been "The Mirror Marathon".

Whichever term applies, it was great. We started on Friday afternoon with a quick introduction followed by the fine grinding of our generated blanks, a 10-inch f6 in my case. The grit sequence was Silicon Carbide, SiC, 220 grit, Aluminum Oxide, AlO, 25, 12, 5 micron and then Cerium Oxide, CeO, polishing agent.

Rough and fine grinding is somewhat "mechanical":

1. Put some grit on the tool and mirror
2. Do the 1/3 center over center "Boogie"; I mean stroke, turning the mirror and "going around the barrel".
3. Go around twice,
4. Dunk mirror and tool, clean off sludge.
5. Do step 1.
6. Do steps 1 through 5, 8 times (this is called a wet), clean your tool and mirror very thoroughly and go on to the next grit.

We did approx 16 wets between the 220 and 25 micron. By the time Friday night rolled around, I had completed the fine grinding and was ready to start polishing in the morning.

"Ah, pitch in the morning, smells like, (sniff, sniff) victory". Pitch, messy stuff, but fun. Was it hard or was it soft? All I know is it worked.
The Cerium Oxide was polishing the glass well and I was ready to start figuring by late afternoon.
Figuring is when the "final" touches are applied to the mirror. The transformation of a smooth sphere to a parabola can be a long process or it can be a short one.
Occasionally a message pops up on the Internet, in newsgroups, etc which goes something like "How Hard is it to make your own mirror?"

Having completed 2 mirrors I can honestly say, "it's not very hard" BUT, there are a few "if, and or buts" included.
Here are a few:

1. Take your time. If you rush, you may end with lots of errors.
2. Keep your area clean.
3. Enjoy the process.

Back to figuring, using CeO you really don't creep up on the final figure. In my case, I had a "very nice" sphere, so the transition was quite short when compared to when I used rouge on my first mirror.

There were some people that appeared to be rushing through things and they spent 3 times as much time finishing.
So how did my mirror end up? It has an "excellent, smooth parabola" but, L I have a turned down edge that is about a 1/8 in from the edge.

As I mentioned, it was a great weekend.
The Delmarva Stargazers are a great group of people, Thank You Don and Company.
The food was excellent.
Steve and Bruce Swayze were outstanding teachers, tutors and testers! A big Thank You goes to them too.

Enjoy the Sky

Ed "Grinder of Mirrors" Witkowski
NOVAC


More from Ed Witkowski
To:    "'atm@shore.net'" 
cc:
Subject:    ATM Testing of 10 inch Delmarva mirror.


Greetings ATMers,
   Finally got around to knife edge testing my Delmarva mirror workshop
mirror.
Guy Brandenburg helped and the results are quite nice.
Here is a message that Guy posted on a few email lists, some how it didn't
make it to the ATM email list:

 SNIP.......
On Friday 3-23-02, Ed Witkowski and I made a Couder mask and tested the
10-inch f/5.78 mirror that he had ground and polished and figured at the
Delmarva Stargazers Mirror-Making Workshop. We looked at it with a plain
Ronchi grating before we made the Couder mask, and then we took
knife-edge readings at all five zones. Here are the results as
interpreted by the program TEX:

Radius of curvature: 115.5
                f/D:  5.78
   Diffraction disc: 0.000152183

 1 ZONE                1          2          3         4          5
 2 h(x)              2.2361     3.1623     3.8720    4.4717     5.0000
 3 h(m)              1.1180     2.6992     3.5171    4.1719     4.7359
 4 hm**2/R           0.0108     0.0631     0.1071    0.1507     0.1942
 5 hm/4f             0.0048     0.0117     0.0152    0.0181     0.0205
 6 D1                0.0935     0.1330     0.1820    0.2235     0.2740
 7 D2                0.0935     0.1330     0.1820    0.2235     0.2740
 8 D12               0.0935     0.1330     0.1820    0.2235     0.2740
 9 D12 -  0.0762     0.0173     0.0568     0.1058    0.1473     0.1978
10 Lamda c           0.0065    -0.0063    -0.0013   -0.0034     0.0036
11 Lamda f * 1e5       3.12      -7.36      -2.02   -6.16       7.36
12 Lamda f / rho      0.205     -0.484     -0.133   -0.405      0.484
13 u * 1E6            -0.54       1.28       0.35    1.07      -1.28
14 Wavefront          -1.42      -0.46      -0.42    0.00      -0.89
        Reference parabola: y = 0.0429592 * x**2 + 0
        passing through (  0.00,  0.00) and (  4.47,  0.00)

Maximum wavefront error = 1 / 15.2 wave at zone 1

Results for individual sets of readings:
        Reading set 1: 1 / 17.6 lamda, Max Trans
Abberation=0.30
        Reading set 2: 1 / 11.4 lamda, Max Trans
Abberation=0.98

----------------------------------------

Ed says that Steve Swayze relied strictly on a plain
Ronchi test and the Ross Null Test, which involves a
plano-convex lens located somewhere between the mirror
and the Ronchi grating. I have not yet learned how to
set up and use the Ross Null test, but evidently Steve
is onto something.

I think I will have to try this workshop next year, if
they still have it!

Ed also tells me that Swayze said that Ed had a 1/4"
turned-down edge all around. I could definitely see
the turned edge, and at first it seemed to me that it
might be a bit too flat in the center. Ed wanted us to
test it, so we did.

Ed also said that the DMSGMMWS folks also didn't take
as much time on each stage as we did; instead, they
only did about 7 to 8 wets per grit size
[pre-generated blanks, naturally], alternating MOT and
TOT every 2 wets. No side-to-side motion during fine
grinding.

They started with polishing pads, but they seemed to
cause lots of problems, he reports -- lots of zones
and 'other crazy stuff'.

Guy Brandenburg
NCA mirror-making workshop.
-----------------------------------------

Ed adds:

I am quite surprised.
Hopefully I can contnue with a few more successful
mirrors.

End of added email.

Mike Mills from NOVAC also "ran the numbers" through his software and here
are his results:

SNIP.....
The results that came back:

>
> Best fit focal length: 57.48 inches
> RMS Error on glass: 1/194.8 waves
> RMS Error at wavefront = 1/76.2 waves
> P-V Error at wavefront = 1/14.5 waves
> Maximum transverse aberration = 1.36 at x=5.0
>
> The analysis showed the turned-down edge very clearly, and it also showed
> a center that is just slightly high, about 1/80 wave!  Masking the last
> 1/4 inch will bring the TA well under 1.0, it might even make it less
> than 0.5.
End Snip......

As to the "short" time between grits, it might have something to do with
the
AlOx we used.
According to Don S of the workshop, the AlOx we used was "shaving" the
glass, rather than pitting the surface,
the result is a smoother surface.

By the way here is the "raw" data:

Snip

here are readings from my 10 inch, what do you think?
mirror size 10 inches
fl 57.75 inches
5 zones 2 readings
2.236 in     .092  .095
3.162 in     .132   .134
3.872       .181     .183
4.472       .226   .221
5          .268    .280
SNip...

Next is coating the mirror and seeing how it performs with the TDE and then
masking it.
Then it is on to my 13 inch project. Oh and actually building telescopes
for
my 8 and 10 inch mirrors :).
Hopefully this summer I do my biggest mirror, a 16 incher.


Enjoy the sky
Grind more and worry less.

Ed Witkowski
Woodbridge, VA



From the ATM List:
John Hutto .... subject: Re: ATM Delmarva Mirror madness
I would also like to thank Don Surles, Steve and Bruce Swayze and all of the other attendees who helped newbies like me make a mirror.

I could have never learned all that I learned that weekned if I had just "struck out on my own".

It was well worth the drive and time to attend, and the food was great!

These guys are a first class bunch for sure!

I am looking forward to having my 8" f/6 coated and assembled into a scope.

I think that I have the necessary knowledge to go it alone for the next project.

Thanks again,

John


Aart Olsen on 03/09/2002 04:59:49 PM

To:    Don R Surles/AE/DuPont@DuPont
cc:
Subject:    Mid-Atlantic Mirror Making Seminar


Don,

I'm writing to thank you for the warm hospitality you and the Delmarva
Star Gazers offered to the attendees of last weekend's mirror making
workshop.  I had a great time and thanks to you and the other experts
there I even ended up with a good eight inch mirror at the end.  It's
amazing to me how the company of a few good people can so quickly clear
up years of reading about the black magic that optical work always
seemed to be.  You're right when you say that doing this is quite a bit
different from reading about it, and for me it was a very enjoyable time
indeed.  Please extend my heartfelt appreciation to everyone who worked
so hard to put it all together.

You didn't solicit specific feedback from us after the workshop and I
won't offer any here, but if you'd like to hear the opinions of the
attendees let us know.  Perhaps it'll make the next one even better.

I hope to see you guys up the next time I'm in the neighborhood.

All the best to you,
Aart
--
Aart M. Olsen       mailto:aart@uiuc.edu        217-244-4688
Library Systems Office     Univ of Illinois Urbana-Champaign




John Glasheen
To: Don R Surles/AE/DuPont@DuPont
cc:
Subject: RE: Solar Prominence Scopes

Hi Don:
My solar prominence scope saw first light on Sunday and it worked like a champ! I ordered and received some rings and a dovetail plate from Ken Dauzat of Ken's Rings and Telescope Accessories ( I highly recommend his products - he does first class work!) and set the scope up on Sunday despite very hazy skies. I wanted to test the setup and thought that I might get lucky and catch a piece of clear sky. Well get lucky, I did. After about an hour, the sky clear substantially and I was able to view several nice prominences. Over a 20 minute period, I watched one prominence start out like a vase of flowers, then grow into a high-arching hook. Only a prior commitment kept me from spending the day enjoying my scope.

My thanks again to Dave for all his excellent work as well as you and the many others that contributed to making that weekend great fun!

Jack Glasheen

p.s. - I'm debating whether or not to paint the scope. There's something charming about looking at it in it's raw state. And I think it might be fun to watch people's surprise when they look through the scope at the quality view after seeing a "Grits" container on the end of it with a "Richfood Grits" label on the outside. ;)