Re: [ATM] A bit of hand polishing advice please................

["John and Bernadine Murray" <onslow@cyberone.com.au>]

G'day Mark,
	Thanks for that, I did a another couple of laps around the barrel.
It is getting slowly better, I'll let the mirror settle down over night and
test in the morning.

Cheers

John Murray
Whyalla
South Australia

-----Original Message-----
From: atm-bounces@atmlist.net [mailto:atm-bounces@atmlist.net] On Behalf Of
Mark Holm
Sent: Wednesday, 22 November 2006 11:11 PM
To: Amateur Telescope Makers
Subject: Re: [ATM] A bit of hand polishing advice please................

John and Bernadine Murray wrote:
> I
> think a touch of tde is coming in. A slightly shorter stroke called 
> for perhaps?

Looks like TDE to me.  I use the old mental dodge of thinking of the light
crossing the mirror at a grazing angle from the source side to the knife
edge side.  It helps decide the "sense" or slope of the shadows, up or down.

I am no expert at preventing or fixing TDE, but I am somewhat soured on
short strokes.  In my bit of experience, they tend to make things worse.
 I'd try for good lap contact out to the edge as close as possible without
getting a ridge of pitch past the edge, then use longer strokes.
 Not radically longer, but enough to make sure the edge really is getting
action.

Probably best to wait for others to chime in.  Like I said, I am no TDE
expert!

--
Mark Holm
mdholm@telerama.com


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