60cm f4.3 mirror

60 CM  MIRROR

This one has always been a dream for me. But the prices of the glass!!  When I started thinking about a 60 cm, the price of a disk was ca 5000 dollar..
Suddenly, I heard about  pyrex glass that was not too expensive. It was available from Newport in California.
April 2004 : The pyrex 610x 45 mm disc arrives from California. It already has a radius of f4.4 . Cost : 980 euro for the disc and 600 euro for transport and taxes.

Date Work
April 9,2005 First work is to grind the backside flat. I used a 400x 19 mm float glass disc and carborundum 240
May   13, 2005 I made a 48×5 cm plaster disc ,cast on the mirror,that was protected by vaseline.I had made a dam of thick cardboard .After a week drying I glued (polyurethane   2 component glue) small tiles (19x19x2 mm) on the plaster .Distance between tiles was 7 mm.. The disc was protected against moisture with 3 layers of varnish.This grinding tool  of course  has to be made fit on the mirror. The progress is checked with the help of little marks on the tiles made with a waterproof inkStroke :   Mirror below ; small W-stroke ; overhang not more than 10 cmCarborundum 180 and 240 ( C180 and C240)The grit is applied as a suspension in water with a little detergent added . It is squirted on the mirror or the tool with a plastic bottle with small opening. I add some after every round. A walk around the table has 8 positions
May 16 C180 finished after 12 rounds . Now C240
May 17 Ink marks still around on the edge tiles after 7 rounds
May 19 C 240 : ink marks gone after 10 rounds , even near edge
May 21 45 rounds 240. Only 4 tiles are not ground.I regularly round off the edge of the mirror and the edge tiles with a 400 grinding stone
June 1 Next : C320Done : 100 rounds C320  and 3 rounds with C600 to be able to see and mark some pits on the mirror.The grinding tool is fitting well
June 2 4 big pits marked within 2 cm of the edge of the mirror.It is quite a heavy job to carry the mirror around!
June 11 Next : C600 : to avoid bigger particles I decant a C600 suspension and use only the upper part. After 200 rounds most marked pits are gone
C800 : after 500 rounds I mark some pitsAfter 5 rounds the ink cross on the mirror is already gone.Pits marked after round 59
June 27 After 100 rounds C800 and 145 rounds Al-oxyd ( 15 micron microgrit) : all marked pits are gone. I treat the mirrors edge often with a 400 stone
June 28 Pity. I discovered a number of scratches.Back to C800. After 40 rounds scratches still visible
June 29 I return to C500 and 600 ; 800 too fine for these scratches
June 30 After 40 rounds : scratches smaller
July 1 After 80 rounds : scratches have turned into a number of small pits
July 3 After 140 rounds : scratches are gone. To C800; 40 rounds done
July 18 Round 135 : finished. Mirror edge and tool edge(the tiles) rounded with stone 400
July 19 On to C1200120 rounds; then on to 20 rounds with Al-oxyd microgrit 9 micron and 22 rounds with 3 micron.No pits or scratches visible.
POLISHING
This time, I didn’t cast the pitch on a plaster tool but chose for a plywood tool, made of 5 discs of 18 mm plywood (diameter 48 cm). On top of that were glued 2 layers if 3mm thick board ( of dfferent diameter, so as to mimic a convex surface). 2 rectangular wooden blocks are glued to the side of the thick disc. They function as grips while polishing.Around the disc came a cardboard dam and the molten pitch was cast through a nylon stocking onto the wooden base. After the pitch had cooled enough I made cross channels with a 10 mm thick piece of wood. This way of making a pitch lap I read from Dobson’s methods. Fitting the pitch lap to the mirror took some time.   I heated the pitch lap with warm water and pressed it with 10 kg. on the mirror. It took several sessions and I had to trim the pitch a numer of times. Pitch squares are 50 mm wide.
Sept. 6 Start of the polishing. The work is heavy!!. Mirror below . W-stroke with 3-5 cm overhang. It is not going well. Tomorrow I will sratch the pitch squares with a sharp knife to ease the polishing
Sept. 7 Polishing is going much better. 45 min ( 3 periods of 15 minutes)
Sept. 11 Total time : 1h45m. Today 4x 15 minutes. When the pitchlap catches, polishing is very heavy work, despite the handles on the pitch lap. The pitch squares have to be scratched often.
Sept. 20 Total time : 7 hours . It is going well because the temperature is not so high.Reflection test( 25 W clear bulb focussed with 50 mmf2 lens on the mirror) : weak till r=25 cm. Edge area still has a quite strong reflection.
Sept. 29 Total time 12 hour ; 2x 15 min. a day is already quite a job! Afraid of arm injury
Oct. 5 Total time 15 hours ; reflection in last 5 cm still obvious.
Oct. 21 Total time 22 hours. Reflection at edge very weak
25 hours of polishing : stop

 

CORRECTING THE MIRROR

I use the Figure XP program for evaluating the mirror figure

Jan 19, 2006 : I made a 25 cm pitch lap from Gugolz 55 pitch with some turpentine to soften it. I didn’t check out the hardness 

Working plan:

  1. Fit the pitch lap  on a 25/5.5 mirror (to get a curve in the pitch))
  2. Work ceriumoxyd polishing powder into the pitch
  3. Cut a star form with 8 points in the pitch
  4. Fit onto the 60 cm and trim the pitch squares.

 

Step 1               jan. 21 ,2006

I rounded off the mirrors edge with the help of a 400 stone.Start of correction.

1a . 25 cm 8 points starlap with 2kg weight on it

Straight stroke 0-1 cm to the right of the center with 5-7 cm passover: 20 turns ( 8 positions per turn).

5 min cold press after every ten rounds.

1b . Large W with 5-7 cm  overhang  2x 1 turn  with cold press after every turn around

 

Step 2

First 10 min warm press with 5 kg, followed by 1 hour coldpress with 2 kg
a. Straight stroke 25 cm lap 0-3 cm from center 3x 10 rounds with 5-7 cm overhang
b. Large W-stroke with 5-7 cm passover 2 rounds with pressing in between

Test : ronchi : sferical with strong TDE ( Turned down edge) . Foucault diffraction ring much brighter on the right side. Also polishing scratches and blotchy surface

Step 3

3a  Increase correction

25 cm lap 30 rounds Straight stroke 0-5 cm ; 7-10 cm overhang

3b  Large W-stroke, mostly on edge of mirror; 10 cm overhang

Test: TDE ca 5 cm wide

Fouc. Test:
zone 7 : 2.2 mm
Zone 6 : 0,65 mm
Zone 5 : 0 mm
Zone 1 : 0 mm

Step 4

4a . First try to get rid of TDE

  • old 10 cm pointed lap( squares are made narrower near the edge) circular stroke on outer zones. Now and then an elliptical stroke to the center
  • circular stroke 2-6 cm from edge: 5 turns around
  • Dito 2-25 cm from edge: 1 turn around

Total time: 30 min.

4b. Different approach: work with 25 cm eight points starlap (with 2 kg)

  1. Tangential stroke 4-8 cm from edge : 30 min
  2. Straight stroke 0-5 cm  from Center to increase  correction: 2x 15 min with 2 kg
  3. Large W with 5-7 cm overhang : 3 turns around.

Ronchi: TDE seems to have lessened.Surface blotchy.Pitch too hard?

Fouc:
7 :   1.9 mm
6 :    1. 3 mm
5 :   1.2 mm
1 :     0 mm           Getting better!

Step     5 .

jan 25 – 2006

25 cm pitchlap (8 points star) : 10 min in lukewarm water and then 30 min pressing with 5 kg

  1. tangential stroke 4-8 cm from edge with 2 kg : 15 min
  2. Straight stroke 0-5 cm from center with 2 kg : 2x 15 min
  3. large W stroke max 8 cm passover

Test: difficult to perform: the light passes through several rooms . Measurements are impossible if the house is warming up.

Step 6

Jan. 26 ,2006

  1. Straight stroke with 25 cm lap +2kg ; 0-5 cm from c and 5-8 cm overhang : 3x 15 min (pressing in between, which is always done during long polishing sessions).
  2. Large W-stroke with 2 kg and 5-8 cm overhang : 5 turns around.

test : Ronchi : looks OK

Fouc. 1 measurement: First with a 7-zone mask

Zone 1 2 3 4 5 6 7
Measurements 0 0,2 0,6 1,0 1,35 1,55 2,05
Parabola  0 1.52 2.81 4.09 5.34 6.61 7.78

Step 7.

I trim the old 25 cm pitchlap. The squares are cut in 4. Smaller pitch squares make movement easier!

  1. 25 cm starlap : straight stroke 0-5 cm from C and 5-8 cm overhang : 50 min
  2. Large W-stroke concentrating on outer zones ; 5-10 cm overhang : 4 turns around

Test: difficult because of the “clouds”in the lightpath!

Zone 1 2 3 4 5 6 7
measurements 0 0,8 1,4 1,8 2,4 3,0 3,6
parabola 0 1,52 2,80 4,08 5,33 6,60 7,78

Ronchi pattern looks regular

Step 8  

Jan. 28, 2006

First, I made a softer 25 cm starlap

  1. Straight stroke with 2 kg 0-5 cm from C and 5-8 cm overhang
  2. The same   30 min
  3. Large W-stroke + 2 kg with 5-8 cm overhang 3 x 2 turns around

Test : difficult because of the “clouds”in the lightpath

Zone 1 2 3 4 5 6 7
Measurements 0 0,43 1,3 2,26 3,0 3,6 4,2 mm
parabola 0 1,52 2,80 4,08 5,33 6,60 7,78 mm

Step 9   

Jan. 31, 2006
25 cm starlap soft

a. Straight stroke with 2kg 0-5 cm from C and 5-8 cm overhang 10 mi
b. Straight stroke with 2 kg 2-5 cm from C and 5-8 cm overhang 15 min
c. Same as b, for 20 min.
d. Large W-stroke with 5-10 cm overhang :5 x 1 turn

I scratched the pitch squares to ensure an easier polishing action.

Ronchi : obvious bend in the lines at r=15 cm

Zone 1 2 3 4 5 6 7
Measurements 0 0,76 1,5 2,6 3,4 4,15 5,0mm
parabola 0 1,52 2,80 4,08 5,33 6,60 7,78 mm

Zone between 3 en 4

Hole in C

Step 10.

Now : how to get rid of the hole in the center and the bend at 15 cm?

For polishing I use Ceri-Hex from now on .This is more uniform but quite expensive stuff!

25 cm soft pitchlap(8 points star)

  1. Straight stroke 10-15 cm from C  : 20 min
  2. Straight stroke 5-10 cm from C   : 30 min
  3. large W-stroke 10x 1 turn around

Always with 2kg and 8-10 cm overhang. Polishing is only easy when I scratch the pitch squares.

Ronchi : looks regular

Fouc. 2 sets of measurements (30min in between)

Zone 1 2 3 4 5 6 7
Measurements 0 0,9 1,67 2,65 3,61 4,47 5,4mm
parabola 0 1,52 2,80 4,08 5,33 6,60 7,78mm

Step 11

Febr. 6, 2006

25 cm starlap   2 kg

  1. straight though center C   :                      10 min
  2. straight stroke 3-5 cm from C           2x 15 min

5- 10 cm overhang
3.      straight stroke 10-15 cm from C 10 min
4.      straight stroke  1-5 cm from C                     15 min
5.       large W-stroke 6×1 turn aound
Measurement:

First I turned down the central heating, closed the windows and waited for 3 hours!
Now the atmosphere was stable and I could make a good set of measurements.

Ronchi : regular
Fouc. 2-4 measurements d averaging

Zone 1 2 3 4 5 6 7
measurements 0 0,7 1,12 2,34 3,28 4,38 5,37mm
parabola 0 1,52 2,80 4,08 5,33 6,60 7,78mm

Step 12.
Central area is too flat: deepen with 15 cm pointed lap.

  1. 15 cm lap + 2 kg straight stroke 1-3 cm from C and 5 cm overhang: 15 min
  2. 25 cm lap + 2 kg straight stroke 0-5 cm from C and 5-10 cm overhang
  3. 25 cm lap +2 kg large W-stroke 5-10 cm overhang : 5×1 turn around
  4. 15 cm lap : same as a
  5. 25 cm lap +2kg : straight stroke 0-15 cm from C and 5-10 cm overhang

It is also necessary to work on the outer zones!

Zone 1 2 3 4 5 6 7
measurements 0 0,78 1,74 2,94 4,02 5,21 6,44
parabola 0 1,52 2,80 4,08 5,33 6,60 7,78
Percent correction 51 62 72 75 79 83

 

It looks like the edge zones are going flat!

Step 13 

2 aims : increase correction  and correcting long outer zones.

  1. 15 cm pointed lap + 2kg : straight stroke 0-3 cm from C :                           20 min
  2. 25 cm starlap( already a bit thin!) + 2kg straight stroke on r=20-22 cm : 10 turns around
  3. 25 cm lap + 2 kg: straight stroke 0-5 cm from C and 8-10 cm overhang     : 15 min

Ronchi : bend in lines at r=20 cm ; also low edge

Zone 1 2 3 4 5 6 7
measurements 0 1,0 3,7 6,2 7,5mm
parabola 0 1,52 2,80 4,08 5,33 6,60 7,78mm

Step 14 

Febr. 8, 2006

Aim: improve edge area and keep the amount of correction

  1. 15 cm starlap : Straight stroke on r=25 cm                      10 turns around
  2. 15 cm sterlap : circular stroke   r=25 to r=28 cm           15 min
  3. 15 cm sterlap : elliptical stroke r=-1 tot r=28 cm         20 min

 

Average of 2-5 measurements

Zone 1 2 3 4 5 6 7
Measurements 0 1,61 2,68 4,07 5,10 6,39 7,67
Parabola 0 1,52 2,80 4,08 5,33 6,60 7,78

Strehl = 0,755               labda/3.5 wavefront error

60 cm step 14

Figure: 0,1R means : 10 % of the radius from the center of the mirror

Step 15

Febr. 11, 2006

Plan : 1. correcting area r=27-30 cm

  1. correcting central area to r=10 cm

I use the old pitchlaps

  1. 10 cm lap circular stroke on r= 28-29 cm                10 turns around
  2. 15 cm lap +2 kg : narrow W-stroke between 5 cm left and 5 cm right of center:5 cm overhang   : 5 min
  3. 25 cm lap large W- stroke 5-10 cm overhang   2×1 turn around

Ronchi : TDE?

Fouc.: Average of 3 measurements

Zone 1 2 3 4 5 6 7
measurements 0 1,68 3,00 4,12 5,27 6,33 7,60mm
parabola 0 1,52 2,81 4,09 5,34 6,61 7,78mm

Strehl = 0,404             labda/ 2.1     Worked too much on C

60 cm step 15

Step 16

Work more on edge

  1. 15 cm lap   Tangential stroke on r=27 cm                   5 turns around
  2. 15 cm lap Straight stroke on r=10-15 cm 5 turns around
  3. 25 cm starlap : large W-stroke concentrated on edge and center       4x 1 turn around

Ronchi : edge area flat and shallow hole in C

Foucault:

Zone 1 2 3 4 5 6 7
measurements 0 1,74 3,04 4,21 5,24 6,41 7,77
parabola 0 1,52 2,81 4,09 5,34 6,61 7,78

60 cm step 16

 

Step 17 

Febr. 15 , 2006

Work on edge

  1. 15 cm pointed lap 2 kg : tang .stroke on r=27 cm ;every 3 strokes one stroke to the center to get a bit of correction in that direction                     10 min
  2. 15 cm lap + 2 kg W- stroke   r=6 tot r=12 cm             4 turns around
  3. 25 cm starlap large W- stroke   3x 1 turn around

10 zone masker made

R=5213 mm

Average of 2 measurements

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 1,31 2,23 3,21 3,84 4,81 5,31 6,11 6,87 8,05
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
procent

I made new pitchlaps from Gugolz ,softened with linseed oil and turpentine.

Pressure test (Texereau) 1kg weight and 1 mm2 surface of pin :4 mm depth in 5 min.

Step 18

Work on r= 13,5 en r= 28 cm

First try with new 35 cm lap:

  1. very narrow W-stroke on r=27-29 cm (edge of tool on that area) : 6 turns around
  2. Narrow W-stroke on r=9-18 cm (edge of tool) : 5 turns around
  3. Large W-stroke ( smoothing) +2kg : 2 turns around with 8-10 cm overhang

I didn’t scrath the pitch squares, with the result that polishing didn’t go well
Test : zone 9-10 still 1,3mm difference!!

Difference 1-10 = 7,7 mm     . Diff . 1-2 = 1,3 mm .There seems to be a TDE

Step 19 

Work on TDE

With earlier mirrors I had great trouble combating this problem ; after using a small tool I had to go back to spherical because of the zoniness.
Try anyway..:

  1. 6 cm pointed lap: short tangential stroke on r=27 cm ;every 3 strokes a stroke to the center to prevent zones.. Light pressure 10 min
  2. 20 cm pointed lap +2 kg tangential stroke on r=25 cm ; every 3 strokes a stroke to the center ; 10 min
  3. 35 cm lap large W-stroke with 8-10 cm overhang : 3x 1 turn around

Ronchi : TDE en bend at r=15 cm

Fouc. : Total correction is 7.8 mm and diff 9-10 is 1.4 mm

Step 20

Work on edge with several tools

  1. work with thumb on r=28 cm 5 turns around
  2. 15 cm pointed lap : circular stroke on r=27-28 cm with light pressure . 30 min Cold press every 5 minutes
  3. 15 cm pointed lap circular stroke on r= 15 cm 20 min with light pressure
  4. 15 cm pointed lap elliptical stroke on r=10 to r=28 cm

 

Ronchi:   – small TDE

  • Bend at r =16 cm
  • Hole in C

Fouc. TDE less ! 2-4 measurements and averaging

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 1,08 2,11 2,88 3,58 4,22 4,95 5,70 6,50 7,51
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
procent

S= 0,306   labda/2

60 cm step20

Step 21

Febr. 27, 2006

Work on edge and center

  1. 10 cm lap: circular stroke on r=27-28 cm ; light pressure: 15 min ;cold press every 5 min:
  2. 20 cm tool +2kg : W-stroke on r=9 to r=15 cm; 5-10 cm overhang: 15 min
  3. 20 cm tool : elliptical stroke on r=10 to r=25 cm ; light pressure : 15 min

Ronchi : TDE visible ; irregular surface in central area

Fouc. Average of 2-4 measurements

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,74 1,59 2,38 3,03 3,73 4,48 5,33 6,12 7,18
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
procent

Hole in center gone; TDE still around

60 cm step 21

Step 22

Febr. 28, 2006
Plan:

  1. Edge: 15 cm tool circular stroke with light pressure on edge : 15 min
  2. central area: 20 cm tool+ 2kg W-stroke within r=12 cm left and right ; 5-8 cm overhang           : 15 min
  3. Edge: 15 cm tool : straight stroke on edge area; every 3 stroke a stroke to the center: 5 min

Ronchi : TDE + bend at r =15 cm

Fouc. Average of 2-4 measurements

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,76 1,80 2,58 3,20 3,77 4,48 5,18 5,83 6,83
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr.of the zone 88 122 94 73 68 80 80 76 118

 

It’s worse,alas!   S= 0,01 en labda/1

Step 23

March 1 ,2006

I am a bit in trouble. Edge no good and correction too small

  1. 20 cm pointed lap +2 kg : large W-stroke with 5-8 cm overhang.More pressure on edge and center : 3×14 min.
  2. 20 cm pointed lap : circular stroke with light pressure : r= -3 cm to r= +25 cm( that is : the center of the tool moves between those radii)

Ronchi : TDE + bend at r=15 cm

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,84 1,82 2,76 3,55 4,18 4,67 5,26 6,20 7,07
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr. 98 115 112 95 75 60 73 111 102

S= 0,049 en labda/1,18

Conclusion; zones 6,7 and 8 radius too short ; too little correction.

Step 24

March 2, 2006

Try to work on the zones 6-8

  1. 20 cm pointed lap + 2 kg : W-stroke to max. r=25 cm(edge of tool goes to r =25 cm) : 35 min
  2. 10 cm tool : tangential stroke on r=28 cm ; every 3 strokes a stroke to the center: 11 min
  3. Smoothing with 35 cm tool : large W-stroke with 10 cm overhang :2x 1turn around

Ronchi : no improvement!

Foucault:

Zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,57 1,35 2,21 2,97 3,80 4,44 5,14 5,90 6,87
Parab 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr. 67 92 104 91 100 77 84 90 115

TDE present    s= 0,318   labda/ 1,165

Step 25

March 2 , 2006

  1. Increase correction

20 cm pointed tool + 2 kg : straight stroke 0-5 cm from center and 5-8 cm overhang : 20 min

  1. Edge: 6 cm tool circular stroke on r =28 cm : 10 min.
  2. More correction and smoothing: 20 cm tool + 2 kg large W-stroke 5-8 cm overhang : 20 min
  3. Smoothing: 35 cm tool : large W-stroke 2 x1 turn around

Result : less correction! Caused bij large W-stroke? Surface zoned!

Average of 2 measurements

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,43 1,3 1,84 2,68 3,28 4,21 4,79 5,61 6,40
Parab 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr.

Step 26

March 4, 2006

Increase correction.

  1. 15 cm tool + 2kg straight stroke 1-2 cm from Center and 5 cm overhang: 15 min
  2. 25 cm tool + 2 kg straight stroke 0-5 cm from C                                    : 15 min
  3. 25 cm + 2kg large W-stroke with 5-8 cm overhang                                 : 15 min.

Measurements: 1 : 0   ; 2 : 0,71 ;       9 :   5,92 ;   10 : 6,86

Step 27

Increase correction

  1. 25 cm star shaped tool + 2 kg : straight stroke 0-5 cm from C and 5-8 cm overhang: 15 min
  2. Same tool: large W-stroke 5-8 cm overhang:                         3×15 min.

Measurements: 1 : 0   ; 2 : 0,91   ; 9 : 6,16   10 : 7,21   Still a TDE

Step 28

  1. Improve edge: 6 cm tool : circular stroke on r=28 cm : 10 min
  2. Increase correction: 25 cm tool +2 kg : straight stroke 0-6 cm from C : 2x 15 min
  3. 25 cm starlap + 2 kg : large W-stroke 5-8 cm overhang                       2x 15 min.

Measurements 1: 0 ; 2 : 0,60 ; 9 :5,98 ; 10 : 7,15

TDE and too little correction

Step 29
a. Work on TDE :15 cm pointed tool : circular stroke on r=27-28 cm : 5x 5 min
b. Increase correction and smoothing: 15 cm tool elliptical stroke from r = – 5 cm to r=27 cm : 5x 5 min

a  and b are done in turn

Ronchi : bend at r=12 cm

Measurements : 1 : 0 ; 2 : 1,35 ;   9 : 6,76 ; 10 : 8,06

Edge still too flat!

Step 30

Again: the TDE!

  1. 6 cm tool : tangential stroke on r=27-28 cm ;every 3 strokes a blending stroke veering off to the inside of the mirror                                                                            15 min.
  2. 6 cm tool : circular stroke on r=27-28 cm 20 min
  3. 35 cm tool : large W-stroke for smoothing: 1 turn around

Ronchi :   hole in C ; bend at 20-22 cm

Foucault:

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,74 1,50 2,30 2,95 3,64 4,69 5,47 6,01 6,94
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr.

Correction decreased

TDE less!

Zone in outer region of mirror

60 cm step 30

Step 31

  1. Thumbing on r=25 cm : 5 min
  2. further improvement of the edge:

a.    10 cm pointed lap tangential stroke on r=25-27 cm; every 3 strokes one stroke veering off aside to prevent a zone :………………………………… 15 min
b. 10 cm tool : circular stroke on r=27-29 cm ………………………15 min.
3.  Increase correction : 20 cm pointed lap + 2 kg narrow W-stroke between r =5 en r= -5 cm and 5 cm overhang             …………………………………30 min.
4. Smoothing with 35 cm tool+ 2kg : large W-stroke 5-8 cm overhang 2 turns around

Measurements: 8 o clock in the morning in closed house and no heating: Foucault image stable!!

Ronchi :   hole in center and bend at r =22 cm

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,99 2,06 2,92 3,79 4,56 5,61 6,37 6,91 7,71
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr. 115 127 104 104 92 127 93 62 95

Correction too large : 30 min was too long! Whole outer area irregular

60 cm step 31

Step 32

I apply the radial stroke with the 35 cm tool to blend the zones.
Lap is placed in the center and moved to the edge; 10 cm overhang.
Move it back to the center and repeat in a different direction. 16 different positions in one turn around.

Total time 3x 5 min with pressing in between.

Ronchi : bend at r=22 cm

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,78 1,56 2,43 3,18 4,03 4,89 5,80 6,38 7,20
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr. 90 92 105 90 102 105 107 68 98

Correction strongly decreased(was to be expected with the large tool)Hole in center gone
Zone still present

60 cm step 32

Step 33

  1. Increase correction : 20 cm pointed lap +2 kg : narrow W-stroke between r=- 6 and r=+ 6 cm ; 5 cm overhang…………..10 min
  2. 35 cm tool : radial stroke (see step 32)   ………………..5 min

Ronchi :   bend at r=22 cm

Fouc. 3-4 measurements   “ spread”  0,05 mm

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,85 1,74 2,55 3,43 4,24 5,18 5,92 6,56 7,31
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr.

Edge is “ rising”

Step 34

Increase correction; less work on edge.
a.  25 cm starlap + 2 kg narrow W-stroke between r=-6 and r=+6 cm; 4 cm overhang : 10 min
b. 35 cm radial stroke with 4 cm overhang : 5 min

Fouc. 3-4 measurements :

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 1,04 1,87 2,86 3,70 4,63 5,55 6,40 7,06 7,85
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
Percent corr.

Too much correction and edge has risen

S= 0,472 en labda/1.9

60 cm step 34

Step 35

35 cm lap + 2 kg : large W-stroke with 5-8 cm overhang: 2x ½ turn around(pressing in between)

4 measurements at 16 o’clock ( after 4 hours stabilizing)

zone 1  2 3 4 5 6 7 8 9 10
Meas. 0 0,84 1,71 2,49 3,44 4,26 5,19 6,00 6,68 7,53
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
procent

S= 0,889               labda/5,48

Great improvement!

60 cm step 35

 

Step 36

Work at 60-80 % radius

15 cm pointed lap (8 mm thick):

a.circular stroke at r=18-24cm;light pressure                       5min
b. elliptical stroke from r= -1 to r=+20 cm; light pressure : 5 min

How the measurements are done:

  • mirror on the stand in the bathroom; doors and windows closed
  • 4 measurements
  • Mirror is turned one quarter
  • After 40 min again 2 measurements
Zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,95 1,82 2,72 3,56 4,40 5,32 6,18 6,81 7,51
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506
procent
corr.

S= 0,831           labda/3.9

Step 37

In the Figure XP program one can choose the radius of curvature to make the correction of the figure easier.

If the edge is less turned up ( 20 nm in stead of 70 nm) ,than more work has to be done on r= 90 to r=240 mm. I am going to try that.

  1. 20 cm tool tangential stroke on r=150 mm; every 3 strokes one stroke       veering off to the edge……………………….10 min
  2. 20 cm pointed lap+ 2 kg : elliptical stroke from r= 10 to r=28 cm…………10 min

test : average of 4 measurements

zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 1,15 1,87 2,54 3,36 4,18 5,14 6,03 6,73 7,54
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506

S = 0,936     labda/7.2

The worst of the measurements still delivers : s=0,931 and labda/6.7 on the wavefront

60 cm step 37

 

Step 38

May 24, 2007
10 cm tapered tool : work on the high zones in the figure

  1. Tangential stroke on r=240 mm: every 3 strokes a stroke veering off to the edge; light pressure ; ………………………………………………………5 min
  2. Elliptical stroke r=240 to r=270 m       …………………………3 min
  3. Circular stroke r= 100 mm……………………………………3 min
  4. Elliptical stroke r= 50 to r=270 mm…………………………4 min

Test : average of 4-5 measurements

zone 1 2 3 4 5 6 7 8 9 10
Measurements 0 1,09 1,85 2,67 3,51 4,24 5,12 5,96 6,66 7.39
Parabola 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506

Undercorrected as a result of working on the outer zones

S= 0,914 en labda/4.8

60 cm step 38

Step 39

Work on the high zones

  1. 15 cm tool straight stroke on r=100 mm with 5 cm overhang; light pressure ….6 min
  2. elliptical stroke r=0 to r=230 mm………………………………………………3 min
zone 1 2 3 4 5 6 7 8 9 10
Meas. 0 0,93 1,83 2,67 3,41 4,22 5,11 5,96 6,70 7,55
Parab. 0 0,858 1,696 2,521 3,353 4,185 5,005 5,813 6,66 7,506

S= 0,989   labda/    14 PV

 

June 2,   2007   02.45

Startest : mirror in sling in 9 points cell

5 mm eyepiece : no astigmatism. Ronchi lines straight

Aluminium + QUARTZ LAYER : Galvoptics Basidon Essex (GB) :             juli 2007

Price : 120 pounds only!