- The Chicago Astronomer -
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OK peeps, Last week we astronomers in the UK had the sad news of Sir Pat's passing.
This has been a bit of a body blow to us in the UK, as for so many, he has ALWAYS been there with the S@N over 50 years.
I had finally started my C8 stripdown only to reach the partially disassembled stage for news of Sir Pats passing to reach us.
Well it was quite a shock, my buddy Davie, "Perthshire skies" around the uk forums, was sitting there saying how sad this was. To say his motivation had gone wasn't wrong.
But I had a job to complete, so I put my emotions aside and cracked on.
This will be the record of the stripdown and rebuild, I must be honest and say it ain't up to Joe's on the picture front BUT I had some incidents that hopefully can be passed on as a learning tool to everyone else contemplating this sort of work.
OK I had finally got hold of some quality IPA. However the use of said diluted/IPA on Celesteron's mirrors was a big open question, one that was undecided.
So I bottled it and went with the lukewarm tap water/washing up liquid approach followed by washing with distilled water and blow drying.
As you can see here is my skanky C8 [as you will see later] but the BIG mistake was that I had it flat.
I undid the retaining ring screws, took the retaining ring out and with my left hand left sitting on the bench moved the retaining ring over to the "removed" stuff pile on the R/H side. As i let go of the ring on to the designated area THE CORRECTOR PLATE FELL OUT OF THE TUBE AND THE SECONDARY HOLDER NESTLED NEATLY IN THE PALM OF MY LEFT HAND!! #shootme#
Well that was a bit of a wake up call, Davie just looked at me and we both burst out laughing, BUT THE LESSON WAS LEARNT, always, always think TWICE do once.
So the disassembly carried on [with the tube pointer upwards slightly) next off was the focuser disassembly and this WAS a pain..
getting the circlip off the shaft as it doesn't have the normal "holes" for any circlip pliers, you have to just muscle it off and hope it doesn't ricochet too far! A poly bag over the rod helps tremendously in retaining the clip.
Then it was just a case of unwinding the brass tube with bearings and then the mirror is sitting on the baffle tube.
Note reflection from mirror, gopping grease on baffle tube, not for much longer.......
Last Edit: Dec 16, 2012 11:19:37 GMT -6 by mojocvh
Post by Chicago Astronomer Joe on Dec 16, 2012 11:50:18 GMT -6
Excellent that we get to follow along with your strip down and modification.
That grease glob is obscene indeed. Get that stuff off the baffle post haste! And put that Dow Corning High Vacuum grease in it's place. Solid stuff and what you got will outlast you many times over.
While the tube is apart, I would encourage you to install another handle in the rear of the cell, for better control and safety. I really like the two extra handles I installed on my C11 and so glad I did it.
Don't those heart stopping moments in this project make you feel alive?
As I said earlier no pics of the primary pre cleaning, BUT after 75 odd minutes of gentle cleaning we are left with this disaster...
as we can see the oily residues from the grease that ran down the baffle previously is proving difficult to eradicate.
So another 45 or so minuted gives us a better example,
so time for something RAD!
I make up a mixture of 25% IPA 75% distilled water and soak the mirror as it's held vertically allowing immediate run off, looks ok. BUT we're now left with the sort of streaking on the mirror we had before visible under UV light..... HMMM...
Anyway, copious flooding with warm water followed by distilled water flushes eventually leave a fairly good looking mirror [sorry it's from a different angle but it was 150% better]
Time to leave well alone.....
Flocking the tube.
This was one of the main point for stripping the C8 down.
After the last couple of hours trials it was a bit of a challenge to say the least and things being what they were there are no photo's of the process as such [we were up to our eyes in self adhesive flocking material that was trying to curl round the wrong way, stick to itself, anything else around and leave air bubbles as well.....]
HOWEVER, one point to know.
Try as I might, I couldn't get the Canons IR auto focus to lock on inside the flocked tube, the above was taken by focusing on the outside of the tube.
Whilst |I had been flaginating myself with my primary David had been busy doing the inside of the secondary. As Joe has pointed out before this ain't as easy as it seems so I was glad of the hand to say the least.
note the three handed alien, LOL.
So it was rebuild time. Copious, but not excessive, amounts of hi vac applied to the baffle tube and, big breath time, in with the primary, it was REALLY hard to push down, no part due to the inherent stiffness of the grease, it felt REALLY GOOD you know....
Focuser and bearings back on, also well lubed with hi vac..
excess removed after fit
The secondary had gained some fibres** from the material and was a wee bit messy soooo I cleaned it. With some BAADER wonder cleaning fluid and a fresh from the bag Baader microfiber cloth followed by breath and cotton wool.
** funnily enough so had the primary by now. A gentle rub down [again] of the flocking material followed by the application of the finest remote DYSON technology removed all of the offending particles, if they come back I'll just throw the tube on the floor, that should move them <KIDDING>
I guess this will always be a downside of flocking but IMO it's well worth it overall.
I used the wonder fluid, microfibre cloth, then breath and cotton wool to clean both sides of the corrector. Tickety Boo.
If you zoom into this pre cleaned image you will see a series of markings across the outer tube, secondary, outer tube in a line
These allowed me to refit the cleaned corrector plate exactly as it had been before.
Had to wait a wee bit to get some light in the tube, in fact in the end plumped for the old faithful Rigel picostar.
HINT. GET ONE OF THESE IF YOU HAVE AN SCT!
Hmm first results were not unexpected..
had a wee play at very rough collimation, got it a bit better, but decided best left for a fresh pair of hands later....**have you figured out the artefact yet?**....
not too bad but needs a wee final tweek followed by a star test later,
something not quite right though...Hmmm
frosty the snowman indeed...
** it's attached to the door
right that's all folks, I WILL get a proper star test imaged for ya, but HEY you know my timeline by now HEHE.
Post by Chicago Astronomer Joe on Dec 29, 2012 7:48:01 GMT -6
Mo asks about the In/Out Thermometer I installed on the C11....
Hi, Joe hope you had a happy Christmas.
Look I'm thinking about doing the same mod as yourself and using a inexpensive in/out thermometer for checking temps in the tube of my C8.
Can you pass on any hints or tips learned from hard earned experience with this modification please?
weather here has been dreadful ie cloudy rain and more rain, hope that snowstorm ain't been too bad for you folks.
All the best and have a happy Hogmanay and a painlfree 'Nerday
hopefully in mid/late January will set up a colmination session with the Hutech 3 laser sct device and the owner is happy for a wee story on our "home" forum, Central Scotland Observers Group, and 'natch will dial one in for The Chicago Astronomer if you want...
It's a really simple job installing a in/out thermometer.
I drilled a hole in the tube near the primary mirror. A lot of glass there, where the temps will soak in and turbulence will be starting from. The hole should be slightly smaller than the sensor, so that it fits snugly and not fall out. I velcroed the base unit on to the Ci700 mount where I had room and looked good.
Some things I would do different.
Having the probe in the tube and the base on the mount means that I must unplug the sensor when I break down the scope after a star party. With the constant handling, the sensor now wobbles a bit...and the open hole when it's removed is a invite to dust. Plugging it with something is just another bit to lose. A better solution is to cut the probe wire and attach a connector - so I can simply leave both in place. This is my second temp gauge, as the first one corroded away - eating away at the circuit board with the trapped moisture in the mount case - even with cracking the case to allow for air circulation. A silica pouch is recommended.
My thermometers also have the humidity readouts - good for estimating dew points. The first one was a Chinese model for very cheap and free shipping. Worked well. The second I got at a local retail chain on discount. Works well, but I like the first one better. Having a thermometer on-site is good. Instant real time point temps and not relying on dis-embodied smartphone data is preferred....especially on bitter cold nights and steaming soaked summer nights.
I have not experienced a great varience in temps between the outside & inside temps - perhaps two/three degrees at the most. I keep the C11 in an unheated/uncooled location, so it's pretty much the same ambient temp.
I think the addition of the instrument will be a good one and highly recommended.
I will be anxious to follow along with your new collimation tool and a Happy New year man!
Chicago Astronomer Joe Founder, Administrator and Chief Astronomer
Telescope/Observatory Docent Facilitator Adler Planetarium & Astronomy Museum
Astronomy Instructor Instituto Del Progresso/IHSCA
Astronomy Program Instructor British International School of Chicago /Lincoln Park Campus
Resident Astronomer Chicago Park District Nature Oasis/Night Out in the Parks/ 606 Trail
Hi folks, some time earlier I promised a review of the HUTECH sct laser collimation device.
Unfortunately during these tests it became apparent that there was "something wrong" with the centring of my sct's mirrors, we could adjust it per se and follow the instructions but the following startest was disheartening to say the least, I also had a airy star patterns on the Hutechs plate
This was pretty galling to say the least, so I put the scope down for a few weeks and trawled all the info I could find.
Looking through the usual sources I found a recurring theme, the name Robert Piekiel.
"Celestron The Early Years" "Testing and Evaluating the Optics of Schmidt-Cassegrain Telescopes" "Collimating Schmidt-Cassegrain Telescopes" "Making Schmidt-Cassegrain Telescope Optics"
aren't that well known here in the UK [as you can't buy them in the UK] and that our astro community is really quite small in the great scheme of things anyway.
So taking the plunge contacted Bob by E mail and after a chat purchased the shorter Collimation SCT book, reason being most of the pertinent info for [hopefully] sorting my scope would be there "direct" in the 72 pages without going and getting perhaps confused with too much info....
It took about 12 days for the book to arrive here in the UK, read it cover to cover the first night, then again before formulation a plan [along with Bob's E mail advice] so it was once more into the fray...
First up was to check the primary for squareness. As it was surgery time took the opportunity to fine up the previous cleaning efforts and to check that the "nut" was solid, the mastic at the rear was doing it's job still and to check for the alignment mark.
All good except, No Alignment Mark! Hmmmm.
So after some head scratching went for the "opposite the focuser" standard to set it up from there.
Rebuilt the bottom end [again, getting good at this] plenty of DC hi-vac grease back on the baffle and that was the first part done with the focusing mechanism reconstructed and locking ring back in place, it was time to check the front end alignment.
Here are the alignment marks on the RIM of the corrector plate as before
they are actually a ^ I ^ with the point of the ^ pointing inwards...
But there's a wee problem. Sitting back with a coffee gazing at the corrector plate I realise that "the mark" that I'd presumed was the alignment mark was some way away from the corrector mark, some way indeed.
Now a right quandary, obviously the point of the exercise is to check both centring and alignments all the was through so....
only one thing for it pull the secondary out of the corrector and dismantle it to check for alignment marks....
I get lucky here, as the secondary comes apart fine, no glue/rtv just two felt washers that are in excellent condition..whew!
Right, so what do we have here? A red arrow and a blue line
E mail with Bob confirms it's the blue line.
The red is the top corner of the 7 of 227 marked on the back of the mirror which can be seen through the substrate. Hey at least I know I've a matching mirror set!!
OK carefully, and I mean carefully, reconstruct the corrector/secondary arrangement getting the alignment marks spot on.
But were not through.
In the "book" it mentions to check secondary for centring in the corrector using a calliper.
Hmm. I've a digital vernier that will do the same [ish] job.
It gives zero difference Vertically and 0.001" difference Horizontally-good enough for government work says I....
As Joe showed us before, the big C seems to have been short of cork some time in the past, I also make up some centring shims and after cleaning fit the corrector plate to the scope using the pre-marked alignment mark and carefully snug down the retaining ring. A rough check follows both from the front AND from the baffle tube checking for centring and alignment.
Fortunately it was a clear night with good seeing.
However the local LP [ oh how I love it ] swamped the picostar artificial star that I was going to use to do a rough collimation so it fell to Aldebaran to save the day and with some minor tweaking
concentric doughnuts front and back of focus!!!
Aldebaran was a scintillating warm orange in focus which was "nice" .
No doubt, more to do to tweak the most from the C8, but there's a certain satisfaction from going to this extent to make sure things are "right".
All of which would have been a hard and frustrating task without some SOLID information to work from.
I can honestly recommend that every sct owner has at least one of Bob Piekiels books in their library.
Post by Chicago Astronomer Joe on Feb 19, 2013 9:00:48 GMT -6
This a a great post.
I re-read it three times and each time a revelation in the procedure. I have not seen those little slots in the secondary housing before...or have not noticed them. It just may be worth to create a slot in mine to check alignment.
Don't hesitate to jot down all the details and try to condense this job.
Hi guys. Sorry to be away for so looong but have been a bit off colour these last few weeks.
Joe, I'll take on board your ideas...have got to the collimation point of airy disks.....next up check out where the offset is coming from when using live view to check above....duff EOS T ring or duff Celesteron T adaptor. Not much but it's there...
awe the best
Last Edit: Mar 18, 2013 16:39:23 GMT -6 by mojocvh