Hi
If yours is NOT a fastar "enabled" system, the following applies.
C14 secondarys have an aluminum housing with a central screw and 3
collimation screws.
It is the one CI scope that the collimation screws do NOT screw into
threaded holes. Therefore if you loosen "any" of the collimation screws,
the secondary will -rotate- if you twist the central screw. Once loose,
it free rotates in the barrel.
The correct alignment is a marker pen mark on the back of the aluminum
secondary backing plate inside the housing. It extends to one edge. That
mark must line up with a similar mark on the back of the Primary and the
serial number etched into the edge of the corrector under the corrector
hold down ring.
The position of the screws on these is arbitrary since the secondary can
be rotated.
Typically the mark on the back of the secondary and on the back of the
primary and the etched mark on the corrector are at the 3 O'clock position
facing the front of the scope. (i.e. 180 deg away from the focuser knob).
If you are careful, you can peer into one of the collimation screwholes
(after removal of course) and gently rotate the secondary with the center
screw (that screw is the only threaded thing holding the secondary in
place so dont turn it with the collimation screws tight). With a light
you should be able to detect the black mark. (you might remove 2 of the
coll screws and shine a light in one and look in the other)
Were it mine, I would take the secondary out and drill a 1/4 inch hole in
the outer housing between two of the screws. Then position the hole at
the appropriate place so I could do a "quick check" anytime I wanted.
If you cant see it, about the only way is to remove the corrector, remove
the secondary housing, jam the secondary with 2 tapered pieces of wood and
remove the middle screw (locktite or corrosion, never figured out which).
Then take out the blasted secondary and "look" at it. You can mark the
side up to where you can see it by looking at the mirror side and put it
back together.
This brings to mind an interesting side effect of this. By using longer
screws for the center and collimation screws, you can -position- the
secondary back in the secondary housing. This would have the effect of
moving the "spherical correction" point back a bit so you can hit the
"design" point for spherical correction. Since the secondary is, in
effect, a 5:1 barlow, you dont have to move it far. Of course, moving it
back too far will mean that the secondary is now too small but I dont know
where the ray traces will take you with this. :-)
Be sure and mark the corrector against the outside under the hold down
ring before removal. This is in case you cant find the serial number.
I had a devil of a time finding it on my C11. The marking was so light it
only showed up in reflected fluorescent light. Go figure. But it should
be at that 3 Oclock position if it has never been messed with.
Exactly where those marks are is a function of the technician that did the
final on the scope. The "normal" practice is as I said but.... the
reality is that the marks all need to align.
Since there are "transport" holes in the back of the rear casting you
might be able to detect the primary mark. OTherwise, you have to take it
off to turn it around. But 99% of the time, they will be in the standard
position.
If you remove the primary and it is an older scope, you will need to grind
two notches about 2 inches long and 1/4 inch deep in the backing ring for
the corrector to get it out. The newer ones have the notches.
Theoretically, it fits but usually the notch thing is safer. Just protect
the primary from the metal dust.
There, wasnt that easy LOL
I would center the secondary housing and tighten it to the point of not
being rotatable or movable. Cork under the hold down ring helps here.
The cork shrinks with time so it can get looser.
Too tight might change the figure on the corrector but it would have to be
pretty tight. The corrector is a 4th order curve IIRC and it is pretty
flat.
---------
Phil Chambers [ptchamb@No-Spam] (S.F. Bay Area - Calif. USA)
On Sun, 28 Sep 2003, Mike J. Shade wrote:
> what is the alignment for the secondary for a C-14? Don't the numbers on
> the front of the secondary "point" about to the Celestron sticker on the
> side of the OTA, more or less?
>
> Amount of variation allowable?
>
> Also, what is the tension on the retaining ring for the secondary? It
> should be turnable with little hand pressure not really not tight, correct?
>
> Mike J. Shade: mshade@No-Spam
> Sonoita Hills Observatory, Sonoita Arizona
>
> See work done at the observatory: http://c3po.cochise.edu/astro
> under the "photographs and images" panel on the left of the screen.
>
> "I like the dark, it's cheap." E. B. Scrooge
>
>
>