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Home > Articles > Other Articles > Equipment/Optics > The Magic Bullet for the SCT

The Magic Bullet for the SCT
By Ronald Abraham - 3/18/2008

I bought a 14" LX200 from Doctor Clay Sherrod in Spring 2006. I was immediately dumbstruck by the quality of the optics which he claimed to have selected from a batch he tested at the Irvine facility to come up with a unit that would put the best Celestron C-14 on the ropes.

There was a bit of mirror shift but otherwise it was as good as an SCT can be - actually better. I discovered that Dawes limit is not an absolute limit for discerning greater visual information with increasing magnification beyond 60X per inch aperture.

2006 was about as rainy a year as we get in Oklahoma, so the scope did not get a lot of use into early Summer. Unfortunately, the electronics stopped working (runaway alt axis) during June and I tried for about a month to resolve the issue with Clay. We finally agreeed it had to go back to Meade. I was distraught when he told me it would not be repaired in time to go to OKIE TEX 2006 with me in October.

From the time it was returned in November, I was frustrated at having had to suffer through the Summer Milky way with only an 11" Nexstar GPS and Cave 12.5" Newt. In any event, the scopes electronics seemed to have been not only repaired, but enhanced with a system update. Unfortunately, the scope was not giving me the quality of image quality I had experienced when I first used in in the Spring. This condition - which I convinced myself was atmosphere related - turned out to be a curse for most of 2007.

Surely those of you own SCTs know how to collimate them, and the need for a Laser collimator is really (supposedly) not necesssary. Fortunately the scope went to OKIE TEX and performed decently - well - sort of sometimes.

After playing around with different manners of collimation, I discovered that the circumfrential cast iron weight mounted between the rear cell of the scope and the visual back was interfering with and tilting the visual back of the scope. The laser revealed that the collimation changed as the diagonal rotated. To resolve this issue, I turned the cast iron weight on my lathe and took off about .025"to eliminate the interference. Evidently, that solved the problem because when the diagonal was rotated within the focuser, the beam barely moved in the crosshairs.

Again - and unfortunately - testing the scope on the first good night thereafter revealed a problem with focusing that seemed to pair up with varying altitude to prevent me from getting a really good image. It was moderately acceptable up to about 350X, but lousy beyond that. I remembered a friend at OKIE Tex mentioned that Meade does not always repair; sometimes they replace an OTA or mount with another that comes up to spec. Naturally - with no resolution in sight - I was ready to give up. The frustration with having such a promising instrument falling terribly short just ate at me. I was resigned to move the Nerxstar 11 into the observatory and just use the LX200 14" for lower magnification binoviewing and largewr fainbt fuzzies.

In February, while working on the Meades focuser to find a solution, the brass focuser screw came loose and fell into the tube. I realized that I would have to pull the corrector and remove the main mirror to get to the screw. This was my first and only time inside the tube, and I only dared to do this because a fellow LX200 owner at OKIE TEX had described the process of OTA disassembly to me and it seemed relatively straightforward.

One of the first things I noticed before I began to remove the corrector assembly was that the lowest collimation screw was not holding position properly. I carefully removed the corrector, placed it on a secure surface and quickly discovered that there were two issues with the collimation screws. One was slight binding of all of the screws, and the second was that they needed a bit of lubrication. Resolving these issues was actually very simple, and in no time I had the secondary responding to even the most minute clockwise or CCW turning of the screws.

Now it was time to fish out my brass focuser screw. As my friend at OKIE TEX stated, you slide the mirror and outer baffle tube off of the inner baffle tube, rotate the mirror 90 gegrees so that it may be carefully removed through the left and right slots of the corrector plate cell. OOPs - something here is wrong. I was exerting an awful lot of muscle to get this chuch of glass and aluminum alloy tube to slide forward. It did move, but not without significant effort. When it finally came off, I set it down on a secure surface and returned to the tube only to discover this horrendous hard red lubricant on the outer surface of the inner baffle. It was stiff and waxy - certainly a stretch to call grease. I decided that this was not good.

I'll preface the final fix by telling you that I have been using a synthetic lubricant at my business for years that is actually supposed to be an oil treatment. As it turns out, this stuff is the most incredible pure lubricant I have ever used. Using this stuff with a needle and syringe has helped me to stretch the service life of bearings by a factor of four. At $25.00 per pint, it should do a good job!

What I did was to carefully use WD40 to thoroughly remove all that red gunk from the inner and outer baffle mating surfaces. I then discarded the hardenned potion of this muck and mixed a much less viscuous combination of the red "grease" and the synththetic lube, and then applied it appropriately. I carefully reassembele the telescope tube and immediately began checking it out.

The first thing I noticed is that the focuser turned more easily than ever before. As I began to recollimate the secondary, I noticed that the former jerkiness of motion from turning the screws had become smooth and precision allowing me to quickly collimate with the laser.

The real test came when I began racking the focus and retesting collimation. It was immediately apparent that the mirror was responsive to the focuser like never before; and yes - that translated into about a 65 -70% reduction in mirror shift. So far I am a happy camper. The next test was to tilt the scope skyward to see what - if any - the effect might be on collimation; there was none.

Obviously, I was itching for the first night suitable for observing, and we had some fine ones here in NE Oklahoma in February. We had several nights when there was dead air with average relative humidity and low particulates. I called a friend to invite him over because he had been the last person to look through the scope when it was really screwed up just a few weeks earlier. He also informed me that he had just gotten a new Meade 26mm series 5000 eyepiece he wanted to try on it.

When he arrived we got the mount aligned and picked our first target of the night - M42. I was just hoping to see points of light and see if either of us could tell a difference. He said "Why don't we try this new Meade eyepiece?" so I told him to go for it.

Now here is the weird part: He took a quick glimpse and immediately exclaimed "I can see all six stars in Trapezium". - "Yeah - Right" I'm thinking. He told me to come look for myself. I did, and there was no squinting or careful breathing involved; I was looking at six clearly defined pinpoints of light. His response was "Whatever you did to this telescope worked; this is way better than before."

Turns out this fat 60 degree 26mm 5 element Chinese Plossl is - in itself - a real prize; My 26mm Televue Plossl was almost as good albeit with a smaller APOV. SO both of us are beginning this observing session impressed.

Despite my location in moderate light pollution, my friend and I began playing hopscotch throuh Leo, Coma Berenicies, and Canis Major. The contrast improvement and new found tight focus made it possible to see dozens of Messier and other DSOs so clearly that there is enough visual information to recognize object orientation and type. This is the way it is supposed to be.

From an amateur astronomer's perspective, I did lots of things that we all know about that are specific to telescopes, but ultimately, the final solution is one that has worked on bicycles, door hinges, and fence latches.

Knowing telescopes or any mechanical apparaus comes with time, study, and experience; but don't forget that sometimes a problem can be as simple as a rough edge or need for a dab of oil. In this case, by following every possible path I could imagine, I went from a problematic instrument to one I would never consider parting with.   Digg it   Reddit   Twitter   MySpace   Stumbleupon  

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