[ATM] Ghost image

[vorblesnak@peak.org]

> I assume that is a Newtonian? Excepting the eyepieces, no optics but the
> primary and secondary? It is not absolutely clear to me but I am assuming
> you mean the ghost is a focused image like the main image but just dimmer.
> You have ruled out eyepiece refections.

Yes, an f4 newtonian.  The ghost is more of a blob than a out of focus
Saturn as it were, but one could tell it was Saturn that is out of focus.

As the image of Saturn moves across the field of view the blob will come
closer to the infocus image.  If I wander around the eyepiece I can find a
spotwhere the blob is not seen.

I collimated the scope by eye, then by laser.  The laser seems to be
hitting the primary and the secondary in the middle.  The original
collimation had vignetted a good inch of one side of the primary mirror. 
I adjusted the secondary so the whole of the primary was visible, then
proceeded.  A friend sent a page from an original Coulter manual
discussing collimation and my final view down the focuser tube looks
nothing like the illustration in the manual.  However, I did not remount
anything, just tweaked the direction a bit.

> Sounds like a second surface reflection. Maybe the secondary is polished
> both sides, maybe cut from plate glass, and a fair sized area of its
> coating is missing allowing a reflection from the back surface.

Now that is an interesting possibility.  I see no holes in the coating of
the secondary, but perhaps it has been cleaned to the point that it is too
thin to be servicable.  The primary has some coating missing here and
there, no big holes.  I was considering sending it off for a recoat. 
Maybe I should include the secondary also.


David Davis
Toledo, OR 97391