(Viewed 12,655 times)

[Chicago Astronomer - Astro Joe]

Collimating the C11...

After the major rehab and mod project on the C11, ( astronomer.proboards.com/index.cgi?board=ATM&action=display&thread=2760 ), I knew I had to collimate the scope. Taking it out for it's first raw test outside of my garage, it showed that the views were decent, but not perfect.

Later on that evening, Chicago Astronomers Bill , Steve and I put it through some primary testing, and found we could nudge it better....and then - it got away from us.

astronomer.proboards.com/index.cgi?action=display&board=StarParty&thread=3219&page=1#12510

Hell, we all have done successful collimations before, but nothing we adjusted and observed could get it back to pin point stars that we have been enjoying for the past few years. Stars were all "comet-like" flared like no bodies business. Using Vega as our test star, for it's angle and initial brightness, perfect focus evaded us big time.

What is going on?

It's just three little screws...!

In researching this gross mis-alignment condition, I'm not alone in this.

Some basics:

What I learned form "Bob's Knobs".....

Celestron secondaries are sticky taped to a flat round metal plate...

The plate looks something similar to the pic above, (Bob's Knobs).

(Which by the way, I finally gave in and ordered me some "Bob's Knobs" for the C11 - as I am certain to take the beast apart again sometime in the future and this will help expedite the collimation. )

There is no spring in these Celestron secondaries and ergo...no "Push & Pull" physics going on. It's a simple teeter-toter thing happening....and why it's vital to loosen one & tighten others in the adjustments of the screws when doing the collimation.


- Something that I did not know before and VITAL.....

There are (3) three optical alignment markers on SCTs.

One is on back of the primary mirror....

There, that fat magic marker line on my primary at 3 O'clock - just below the serial number of "5967". An easy landmark and across from the focusing screw at 9 O'clock - as we face the mirror C.P. side.

Second the serial number engraved on the Corrector Plate...

And third...

There is a marker line somewhere on the secondary baffle that aligns with the Primary mirror and the Corrector Plate....and they should all line up at about the 3 O'clock position together - very simple now....

Now, I have been careful to mark and keep the optic train in alignment when dis-assembling, but things happen and perhaps were not placed back properly. And also...the secondary housing is easily rotatable and might have turned.

The three screws on the secondary should also from a triangle with the apex or point "up", with the lettering on the outside of the secondary housing - right side up.

So, first thing is to check the alignments of the three....an easy procedure.

Then, if good...there's that annoying coma stuff on stars and bright points of light. Not only did we use stars to work on the collimation at our session, but bright lights on buildings in Chicago's magnificent skyline. All had comet-like features.

It's not just a little mis-aligned now...but way off!

The point is to tighten the screw opposite the head of the comet. In the middle of our session and with visitors to attend to, sometimes it was foggy to remember which way to adjust. And to compound the situation the secondary shadow kept "circling" the center, not centering.

Damn it!....

And important...if your star is at the edge of the FOV, (even flared), and it goes out of the FOV while making an adjustment...you are going the wrong way. Stop and do the opposite of whatever you did.

The problem with large aperture scopes, is that our arms aren't long enough to observe the star/point of light - and make the adjustments ourselves. We need a loyal astro bud to assist. But...I'm thinking of using a webcam to make it a one man procedure. Using a laptop, I can stand away from the eyepiece and use the screen to guide me as i adjust the screws. Now, all I need is a USB Cam.


More as we dig deeper into this and start the airy-disk testing again after I check the physical components for factory alignments.

But, here are two great Collimation pieces on Astromart:

www.astromart.com/articles/article.asp?article_id=718

www.astromart.com/articles/article.asp?article_id=548

[patrickm]

[Paulie pchris00]

Jun 6, 2011 10:59:19 GMT -6 patrickm said:

Sitting back and watching the collimation "work itself out?"

[Chicago Astronomer - Astro Joe]

I don't like kettle corn.

[patrickm]

It's not for you anyway!

Get back to work on the C11! We're all counting on you.

[Chicago Astronomer - Astro Joe]

[Chicago Astronomer - Astro Joe]

[patrickm]

See? It does all work itself out.


[Chicago Astronomer - Astro Joe]

Alright kids...

What's going on with the C11...

Let's start with the basics...alignments of the Primary mirror, Secondary mirror and the Corrector Plate -


The Primary doesn't spin on the baffle, as the focusing screw juts out the back of the cell and is securely attached to the rear of the mirror - and it will be our baseline to go from. The orientation marking at the rear of the mirror is at 3 O'clock - 90 degrees from the top of the tube.

The Corrector Plate was off almost 90 degrees and the secondary was almost off by 180 degrees. My marks were still good from last year's dis-assembly project...so I can only defer that Celestron installed them wrong or most likely, who every had it before me goofed it up.

With that, I work in the garage this time, 'cause I don't feel like lugging the OTA to the Workshop. Laying a work shirt on the floor, I set the tube down and remove the C.P...

The auxiliary handles I installed on the rear of the C11 come in very handy for support feet in keeping the OTA upright and steady.

In researching collimation problems with other SCT users, some noted that the lock down collar for the primary was loose, causing gross tilting on the baffle. I reach down to the collar here......

...and yep...it's loose!

I don't have the necessary sized spanner wrench to tighten this up, so I elect to tap in into place with light hammer and screw driver...

I check the snugness and feels good. I want to tighten it more, just because, but leave well enough alone.

Nothing else to do here...let's look at the secondary...

There is supposed to be a mark of sorts somewhere on the secondary...but I ain't finding it.

I unscrew the secondary baffle..and there is a mark...a gouge more like it...and I don't think it's what I'm looking for. But, something bothers me...

All around the secondary housing, there is a gap...

...about a 1/16th space...enough so that the secondary swims around in the Corrector Plate opening - making centering/aligning the optical train difficult.

We are gonna have to address this when it all goes back together, but first...I have an idea...

Bringing the C.P. with me to the workshop, I examine the secondary baffle...

It's mighty shiny.

I have read where others have flocked their secondary baffles...and so shall I. It's already off the plate anyway, eh?

I measure off the same material I have been using for all my other flocking needs and cut me off a nice sized hunk.

Lining the I.D, we have a nice light absorbing blanket for the baffle. I feel that every surface we can knock off sheen, glare and light bouncing around is good...especially for urban astronomers who have to contend with intrusive light pollution.

It looks good.

But wait...uhm...that Outer surface area...is looking kinda bright...yes?

I measure off and cut me another hunk of flocking material...and do the outside...

I use clamps and rubber bands to help hold down the material. The outside is more of a challenge, as it's not pushing against anything to keep it in place - just the spray adhesive to secure it.

While the glue dries, we spend some more time cleaning the Corrector Plate, as no matter how careful one handles it, smudges magically appear...

After the solvents, I find the plain breath fogging and cotton balls, ( a lot of cotton balls), work the best and leave the surface sparkling.

But, there is still that matter of the 1/16th space between the C.P. and the secondary. I cut me some strips of "pleather" and use them as cushioned spacers...

I place four around the secondary housing and against the C.P. Feels firm and yet still enough room for expansion. I feel better in doing this and I think it will serve it's purpose well.

Back to the secondary baffle....

I elected to keep a black rubber belt around the baffle permanently, to help keep the material in place...just in case. And the baffle is slightly Conical funnel-like in shape and I had to trim the material to fit after gluing.

I like it...almost Woolly Mammoth-like...

I bring the Corrector Plate back to the garage and set it aside while I blow out the OTA with about 80 lbs of air pressure...

And one final cleaning with the cotton balls on the C.P.... (a lot was used in this project...I mean a lot).

And coordinating with the alignment marks I left with blue masking tape...we set the C.P. in place and make sure all marks are at the 3 O'clock position and the apex of the three collimation screws is "Up"....

But, will it image well...?

Dunno, but first things first...sandwich and an RC....

[Chicago Astronomer - Astro Joe]

Testing the adjustments for collimation...

Around midnight, I elected to test out the tweaks. The skies were clear, although hazy...and very humid. I set up the C11 outside of the garage and snug the collimation screws down as a starting point.

I use my trusty Fisk Generator smokestack in the distance and test out the views on the red safety lights...

It's not bad, but off.

I bounce back and forth between the eyepiece and adjusting the screws...

I was getting closer, with the secondary shadow making it's way toward the center...

But no concentric circles....what we need is - a star.

I slew the scope toward Polaris, this way no need to track...

And it starts to come together, as it should.

Problem here, is that the angle is high and difficult for me to ascertain which screw is which, being solo and all. What I need is a pointer of sorts.

I use a small clamp and works to direct me whats what up there.

And in no time, Polaris is looking good...

And, apparently just where I set up, a electrical service line intersected the Pole star almost in the middle...and sorta helped in collimating. I should mark this position for future reference.

And before I knew it, I was getting pinpoints to my stars!.... #Yay#

Now, the collimation is not 100%, but very close. I must have climbed up and down that shaky ladder this side of fifty times and for now....good enough. I will wait until a sympathetic astro buddy assists to get the C11 as close to perfect collimation as we can get it.

But....

With a working scope again, no sense in wasting a clear night...

Using a light blocking shroud, I scan the skies and enjoy time alone with the cosmos...well the Police did stop by, backed-up from the street and and wanted to know about the scope and talk astronomy. Gave them my card for future inquiries.

But, it was now 3:00 am and time to pack it is, and besides...it was very hot...

According to the C11 in/out thermometer, there was only a 2 degree difference between the interior and exterior temp...but I think the humidity was greater than 75%...

Ready for the next star party...!

See...it all works itself out... #bow2#

[patrickm]

Congrats!!

But I don't think whatever or whoever IT is was the one doing the research, dis- and reassembling the CT, and
running up and down the step ladder all night.
;-)

[Paulie pchris00]

Glad to see it's back to working order.

[patrickm]

!

Attachments:

[Chicago Astronomer - Astro Joe]

I prefer my Omega-3s in capsule form.

[RobbW]

joe, you truly are an astronomy rock star!! Congrats on getting the beast back into shape.

[patrickm]

I remember reading on Cloudy Nights about a dude who made a wooden reacher thing with a notch cut into that would allow him to adjust Bob's Knobs while looking through his eyepiece.

If anybody could make one, and improve on his design, it's Astro Joe.

[Chicago Astronomer - Astro Joe]

joe, you truly are an astronomy rock star!!

Chicks dig rock star Astronomers!

[patrickm]

There is a saying that all astronomers wanna be rock stars, and a few rock stars wanna be astronomers...or something.

[Chicago Astronomer - Astro Joe]

One day (night), soon....

...all will see it the Chicago Astronomer way.

Then all will be right.

[patrickm]

GL!