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

["Bill Kelley" <flex@commspeed.net>]

Ross,
Your post says the link is a Ronchi image inside and outside of focus. If 
your analysis is correct the first image is OUTSIDE of focus etc.,
Bill Kelley

>           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
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