Re: [ATM] Ultimate Collimation

[johncdeitz@comcast.net]

Hello Bruce: When you give it a try, do it without the reinforcement ring as when the image passes over the ring it is lost. 
John
 -------------- Original message ----------------------
From: "Bruce MacDonald" <brumac@gmail.com>
> John,
> I'd like to see this in action before I deliberately remove any of my
> mirror's coating, even if it is in a spot that does not matter :)
> 
> However, I can vouch for one thing:
> I centre-spotted my primary using a reinforcement ring, and that was
> good.  When later I came to question the original placement of the
> ring, I found the exact centre of my mirror, and placed a single tiny
> black dot there.
> 
> Using the autocollimator with the black dot there made a big
> difference.  When approaching "perfect" collimation, I see ghostly
> images of the ring-and-dot, which when they converge tells me that my
> collimation is "as good as it gets".  Somehow, I find this much easier
> than ever I did with the ring alone.  Could be just me.
> 
> Also, I know what you mean by wiggling the autocollimator flashing the
> circle.  I take that to mean that at that point, the collimation error
> is less than or equal to the mechanical limits of my focuser.
> 
> The downside of the above is that it must be done with a reasonable
> amount of light.  I've been able to do it within about a half hour of
> sunset, but after that it becomes increasingly difficult.
> 
> --BM
> 
> On 9/2/07, johncdeitz@comcast.net <johncdeitz@comcast.net> wrote:
> > Hello Gang: Try this for the ultimate in Newtonian Collimation-
> > 1) remove reflective coating in center of mirror, about 1/8 inch
> > 2) if mirror cell is solid provide hole through cell at center
> > 3) shine a light at the hole from behind the cell (I use an LED with variable 
> brightness so as to preserve vision- this fits in snug hole at center of the 
> back of mirror)
> > 4) using an autocollimator eyepiece, with the optics roughly aligned, you will 
> typically find two spots of light from the LED (or flashlight etc.). Tweak the 
> mirror to bring these two into one and you will see an additional reflection 
> that is quick to change position- this is very sensitive method! Bring all three 
> head-on and your view is flooded with light as with conventional autocollimator. 
> You will find enough play in the autocollimator that his spot will wink on and 
> off as you play with the autocollimator in the focuser.
> > This method offers the following advantages:
> > 1) you can follow the whole action continuously as the cell is tweaked, unlike 
> with the conventional use of autocollimator
> > 2) can be performed in suboptimal seeing with accurate results
> > 3) no problem with off-set.
> > 4) can be performed without ruing night vision so you will not hesitate to 
> repeat.
> > 5) can even be done by one person!
> > John C. Deitz
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
> >

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