celestron ed100 upgrading focusser

[kniclander]

anyone used this on a celestron ed100?

ScopeStuff

any reason why it wouldn't work?

thanks

[spaceboy]

You will need one of these also Agena AstroProducts Crayford Focuser Adapter for Celestron C100ED Refractor to fit the focuser to the OTA

[kniclander]

isn't that what the adaptor ring on the scope stuff website does?

[spaceboy]

This may explain better http://stargazerslounge.com/discussions-scopes-whole-setups/150884-flange-size-crayford-fit-celestron-ed100.html

[kniclander]

thanks spaceboy - I think the gso crayfords have the 86mm flange so the adaptor screws to the scope and the focusser is screwed to the adaptor. agena sell the focusser and the adaptor so hopefully they'll fit......

[spaceboy]

You are correct the GSO dose come with the correct flange but the GSO focuser is not rated very highly compared to similar priced alternatives. Not to mention for some reason the draw tube is not blackened on the internal sufraces. No big deal as it can be painted but to me this dosen't give a good first impression.

[kniclander]

aah, that's interesting - the reviews looked good (although I suppose I was looking at reviews on Agena's own website....). What's better (bearing in mind I am both poor and tight....)

[spaceboy]

Nothing beats the GSO price I'm afraid as the flange is included but for almost the same money a better focuser can be purchased. (if that makes any sense) Skywatcher Dual Speed 2"/1.25" Crayford Focuser | Telescope Accessories | Rother Valley Optics You then have to buy an 86mm flange from TS for £30 odd and the agena adapter which you'd have to buy in addition to what ever focuser you buy (except moonlite). If you search SGL you will see there are several members who have upgraded focusers on their C100ED's. Most of the threads will include all the links you need.

[kniclander]

Thanks Spaceboy. I'll have a think

[ollypenrice]

If there's a Baader Steeltrack that fits then that would be my choice. Or a Moonlite.

I'd be deeply suspicious of most of them, to be honest.

Olly

[kniclander]

er, I'm really just looking for something that will be a decent step up from the supplied one (visual only). I'm certainly not going to pay for a moonlite that would cost about twice what the scope cost me or the steeltrack which would still cost more than the scope.

[MjrTom]

Remember that the focuser is half of the scope

Since its moving parts the engineering is important.

[ollypenrice]

Right, for visual only the focuser is far less critical. The thing is, though, that the scope really does have optics that merit an excellent focuser. It's a stunning objective. But you're right, it isn't so critical with just an EP to support.

Olly

[spaceboy]

I found that when you total the cost up of adding a focuser to the C100ED that even if you picked the scope up cheap you would have been better of just getting a S/H SW ED100 with better fittings in the first place.

[MjrTom]

Right, for visual only the focuser is far less critical.

Well it is if you are into planetary/lunar viewing or double star splitting at high magnification.

[kniclander]

I found that when you total the cost up of adding a focuser to the C100ED that even if you picked the scope up cheap you would have been better of just getting a S/H SW ED100 with better fittings in the first place.

yes, that's why I don't want to spend too much on the focusser:)

[A McEwan]

I went the GSO route on my C80ED and it worked out fine. But on my latest C100ED I simply stripped the r&p focuser down, degreased it, shimmed the drawtube in the focuser body using PTFE tape (for gaming mice off ebay), relubed, reassembled and carefully adjusted the tension. It now works a whole load better and cost me nearly nothing (£1.65 for the tape). Collimation is now perfect and consistent and there's no image shift or slop when focusing.

Besides, Rack & Pinions are the new black!

Ant

[kniclander]

£1.65 - is there anything cheaper??

seriously, thanks Ant, I'll give it a go.

Is there a "standard" PTFE tape or should I look for something super smooth etc? And how much do you put on? Just a strip at a time until the drawtube's snug?

Also, how do you adjust the tension? is that the 4 little phillips screws underneath?

Thanks again. I'll have a google and see if I can find any more info.

[A McEwan]

Oops - sorry, I exageratted slightly. It's actually £1.63 not £1.65: teflon mouse tape | eBay

Right, here's what I did, step by step and the things I used:

Toothbrush, WD40, scraps and cloth rags, PTFE mouse tape (as above), scissors, collimation eyepiece (as shown on this page: Refractor Collimation), allan keys and small cross-head screwdriver, matt black paint or black marker pen, double sided sticky tape.

First off I checked the collimation and thoroughly examined the focuser to see what adjustments made what difference to the collimation and to the focusing action. In my case, the circles as seen through the collimator eyepiece were adrift to the down direction, so putting upward pressure on the drawtube pulled them back into alignment. Theory: the drawtube needed to be shimmed UPWARDS.

The fact that I could put enough pressure on the drawtube to move the alignment showed that the drawtube was slack within the focuser body. Hence shimming would have ben needed anyway, even if the collimation was dead on.

The actual focusing action was ok, but slightly sticky in places. Also, the rubber bands round the focus knobs actually slipped round without turning the focus shaft.

I loosened the two very small recessed allen bolts in the top of the focuser body. These apply pressure to a strip of teflon (or similar) which sits atop the drawtube, inside the body, and helps to even out the travel of the drawtube. I loosened the bolts until they were completely loose but not removed. They are TINY. They get lost easily.

I then turned the telescope over so that the underside is at the top. Loosened and removed the four cross-head screws that hold he rectangular plate under the focuser. Removed the plate as well, and the metal tension-spring piece inside. All were coated in sticky grease.

I then slid out the drawtube and removed it.

Next, WD40 was used to remove the grease off EVERYTHING, including the inner recesses of the focuser body, where it tends to accumulate. I also degreased the rack on the underside of the drawtube, and cleaned the grease off the focus shaft, pinion and all. I then applied some matt black paint to the leading edge of the drawtube and left it to dry while cut some very fine strips of the PTFE tape usin scissors.

Inside the focuser body, on the lower edge, are two guide strips. These allow the drawtube a smooth travel, theoretically. In fact, they were quite sticky and as the collimation test had shown, were not "high" enough. I cleaned them off and applied the long narrow strips of tape to them, building up their "height" by one layer on each. The tape sticks very well but is a fiddle to apply. Patience is the key.

The teflon strip that sits in the top of the focuser body I also cleaned. If necessary I could have applied PTFE tape onto that but it felt very smooth already so didn't bother....

Next I applied a thin layer of grease (Castrol, about 25 years old...) to the pinion gear, the parts of the focus shaft that contacted the focuser body, the spring-clip thing, and the rack. A thin layer and spread lightly over all the contact surfaces. I also put a dab in the focuser body sections where the focus shaft rests and through which the rack under the drawtube travels.

Then I reassembled and tightened up everything to "not-quite-tight" and checked the collimation again.

Collimation was alomst dead-on, but the drawtube still needed a "nudge" upwards, slightly offset to one side, so I disassembled again and put in another layer of PTFE tape on the guide strip that needed raising. Reassembly and testing showed collimation to be spot-on.

Then it was a matter of tightening everythin up and adjusting the tension to taste. I nipped up the four screws on the underside plate and then turned my attention to the two tiny recessed grubb screws on the upper body. These control the tension applied downrawds by the teflon strip, remember? So by careful manipulation of these you can balance the tension at the front and rear end of the strip so that the motion is smooth and even in both directions with no "slop" when changing direction. This can be further balanced by experimenting with the four underside cross-head screws, but generally these shoule be tightened up fairly well, but not too tight!

Finally, some continued racking in and out helps to spread the grease over all the surfaces, after which another bit of adjustment on the screws may be required.

The end result is no slop for the drawtube in the focuser body, no image shift when changing direction while focusing, and a good firm feel to the focus motion.

To fix the slipping on the rubber rings on the focus knobs, I remoived the rubbers and applied some double-sided sticky tape round the rims, then put the rubbers back on.

Took about an hour in total and resulter in a perfectly usable focuser and dead-on collimation!

Hope this helps,

Ant

[kniclander]

Ant, that's great - I'll give it a go....

[spaceboy]

If you don't mind Ant, some pictures to complement your superb how to guide.

[MjrTom]

Very nicely done

[kniclander]

I'll send you my pics of a pile of broken parts shortly.....

[A McEwan]

Thanks SB, I didn't have time to deconstruct and photograph - I wrote it in a hurry! Pics look fine and very representative. The other plus side is that no matter how little the improvement is, you can just keep redoing it until it's right.

Oh, final addition - place a wanted ad for a 2" compression ring visual back for Synta / Celestron refractor drawtubes. It makes for a much sturdier fitting for heavy diagonals and eyepieces and really finishes the job off nicely.

Enjoy!

Ant

[spaceboy]

Or make your own out of what you got on a hobbie lathe