Bob
):-{])) <---- madden@netcom.com madden@svpal.org Remember amateur astronomers: "keep looking for the next Universe"
On 8 May 1995, Richard Combs wrote:
> Reply to: RE>>Coma /Collimation
>
>
>
> --------------------------------------
> Date: 5/6/95 12:12 AM
> To: Richard Combs
> From: atm@best.com
>
>
> >The coma is present or slightly more pronounce at the edge of field in the
> >right side perpendicular to the optical axis. In my mind, I would tweak the
> >focuser setting screws on the opposite side bringing that opposite side up
> >in order to tilt the focuser aperture in the direction away from the coma. I
> >will try this tommorrow in fact and see if the coma becomes symmetrical. I
> >wonder if anyone checks this in their scope as a matter of habit. To tell
> >you the truth, I've always thought that stars tell the most accurate tale of
> >alignment and that these devices can be jiggled in the focuser enough to
> >make their readings ambiguous.}
>
> Don't forget that if you adjust the squaring on of the focuser, you will need
> to check the diagonal rotation adjustment, and the primary alignment. The
> focuser is pivoting at its base, and so the image plane will change its
> position. You need to tweek the diagonal rotation adjustment and primary
> mirror alignment to bring the center of the FOV back to the center of the
> focuser.
>
>
> >See my comment above regarding collimation devices. I once borrowed a
> >friends lazer collimater without instructions. What I noticed is that any
> >pressure on the side of the laser tube when in the focuser made the beam
> >wobble. Which was the true and accurate reading? Maybe a conventional
> >Cheshire set would be better.
>
> Irregardless of whether you are using a laser collimator or
> sight-tube/cheshire tools, you can only be as accurate as your sloppiest
> component, usually the facuser. The Crayford focusers seem to be the best
> design so far. An ultra-precise alignment tool won't help in a loose facuser.
> I find a good sight tube and a cheshire adequate for my needs. The laser
> collimators can be very accurate in principle, but they sometimes are not
> build as accurately as they could be. And I believe you should be confident in
> the use of the traditional tools before you would use a laser collimator,
> because you must understand what you are doing for them to produce acceptable
> results.
>
> As Chuck said, Al Gorski and I will be showing a video on collimation at RTMC.
> We will be bringing about 30 copies for sale at $20. And Lumicon has about a
> dozen copies on the shelf. I don't think they will be advertising them, they
> just wanted to make them available to people who buy scopes off the showroom
> floor. You could get one if you call. But at RTMC, I'l autograph your copy for
> free. Gee wiz!....RICH
>
>