From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: "Jack Schmidling" 
>
>I am trying to set up my 4.25" F 4 for "wide field" CCD
imaging and am have
>trouble getting rid of coma.
>
>First question, is it possible to get a coma free field over a 1/2" with
>this system?
>
>Second question, when collimating on a star, I can not get the diagonal
>shadow centered on both sides of focus with the same mirror tilt.
>If it is centered inside it is not outside and vice versa.  Is this a
>symptom of a problem elsewhere in the alignment?

Hi Jack
 I assume you are talking about a Newton. If so, the shadow
should be off center for both inside and outside of focus. This is called
offset. An F/4 will have noticeable offset.
 Can you be more specific? What type of telescope are you talking
about.
Dwight

 >
>js
>
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