From: John Murray 
To: Amateur Telescope Makers , Mirror Matic
        
Reply-To: John Murray 


Morning All,
        I've made the intermediate zone masks using Couder Mask, cut them out
and
took my first set of reading with them tonight. I started with the centre
zone of the intermediate mask and measured outwards. I interleaved my
readings with the main masks and naturally ended up with 8 zones worth of
readings. I saved the readings into FrontSix, had a look at them using
sixtests and then for the fun of it I used Diffract to see what it should
look like.
        The image Diffract generated using just this one set of data matches
well
with the actual picture of the mirror at
http://www.users.bigpond.com/imasloth/110minfiguring100lpigrating6mmoutsider
oc.jpg This was taken using a 100 LPI ronchi screen 6? (maybe 8mm) mm outside of ROC.

This is my Mirror with intermediate zones 197.000 mm, 46 mm secondary Mirror
Foucault
moving source
radius          radius
Intermediate    main
18.892 0.000    39.299 0.250
49.774 0.700    62.663 1.780
70.077 2.110    78.967 2.510
85.531 2.855    92.392 3.010
2005mm Radius of Curvature


FYI, pasted below are 5 readings using only the main zones.

                zone1    zone2 zone3  zone4
Zone Radius     39.30   62.663 78.967 92.392
1               0       0.550   0.830   1.120
2               0       0.530   1.470   2.080
3               0       0.200   1.040   1.400
4               0       0.200   1.200   1.850
5               0       0.480   1.140   1.800

I don't know whether results can be split into just the main OR
intermediate zones or whether it would be valid to average the main reaings
and add in the intermediate readings or whether it is best to get all of
the zones at the same time. Any thoughts or comments? As usual more
questions than ideas but I hope to get there with a few more years of
practise.
        BTW, I'm considering going back to fine grinding due to accumulated
dings
on the surface. If I do, A thought has occurred to me. Using the original
tool on the machine, I'll need to re-establish the stroke and eccentric
position settings. Once this is done and I am ready to go to polishing
again, would polishing pads be ok on my fine grinding tool.(remember, this
tool goes onto my machine) I suspect the majority of my problem polishing
was the low temps we are currently experiencing. This I believe prevented
the lap from properly conforming to the shape of the blank even though I
was cold pressing for a long time. If this is so, it may prevent the zones
I was developing. If this is ok, then I could save the lap just for the
figuring stage.


Cheers

John Murray
Whyalla
South Australia
Check our web page at http://astronomy.sa86net.com ATM and M-O-M stuff.
Latest Ronchigrams only at http://www.users.bigpond.com/imasloth/

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