[ATM] Comments on Ronchigram of f4.8 mirror pls

[Ross Dawson <rossco@dawsons.dyndns.org>]

Hi folks,
           I've just dusted off my mirror making gear after a few years 
since my last attempt to get this mirror made.  It's my first attempt at 
making a mirror and before I start I'd appreciate some comments on the 
mirror before I go off in the wrong direction, get frustrated and put it 
away again.

The mirror is a 9 1/2" f4.8 (or there abouts).  A Ronchi image of both 
inside and outside of COC is available here 
http://www.dawsons.dyndns.org/~rossco/atm/ronchi.htm (it's tiny 13K so 
no need to worry about download limits)

The quality of the image is not the best it was taken by a cheap CCD 
camera but I think it should be good enough to get an idea.  The unusual 
dark spots at the bottom of the 2nd image is just muck on the mirror.

My interpretation of what I see is as follows.
I have the dreaded TDE around about 1/2" from the edge
There is a hole in the center (it was much larger as the lap was way to 
soft and dug a hole in the middle)

I thought I should go back to basics and work MOT 1/3W strokes to try 
and bring the mirror back to a sphere.  I'm not sure whether this is 
correct though as I might dig a bigger hole in the middle whilst not 
doing much to the TDE.  I wouldn't be opposed to masking the TDE but I'd 
like to reduce/remove it though.

Oh the lap I'm using is VERY hard.  I plan on continuing with this lap 
but I assume I need to ensure good contact by warming the lap in water 
and then a good press to ensure contact.

Any comments would be greatly appreciated and might just get me back on 
track towards first light.

TIA

Ross
_______________________________________________
ATM mailing list http://www.atmlist.net/