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Calling time on Crayfords.


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Speaking from my limited experience, the standard Crayford on my MN190 was a bit ropey, and had a couple of sticky points in its travel. However, since changing it for a motorised Moonlite I've been pretty happy with it. HOWEVER, I'm more happy with the ability to focus whilst scrutinising the monitor than I am with it being a Crayford. The only R&P I have ever used is the one on our old Vixen 80M, but it has always proved to be fairly accurate, and best of all simple. So right now, my experience puts me firmly on the fence, a position that is not healthy for my posterior.

My main concern is about choice. Part of my reason for being anti-Mac (even now that I work in a University with a Mac fleet) is because I believe the consumer should have choice about what they buy, in as many or few aspects as they wish. For that reason, I would like to see the focuser as an option to be chosen at point of purchase. If that caused one type of focuser to prove more popular for whatever reason, be it functionality or price, then I would accept the decision of any company to cease production of the less popular focuser type. In other words, let the consumer vote with their feet.

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The crayford on my ZS66 was slipping and I was able to tighten it with an allen key. The Locking knob has an allen socket at it's centre. (details should be in the instruction booklet that comes with the scope)

Sure but the ZS66 focuser hasn't a hope in hell of holding big CCD gear. This is well known. Mine can just about cope becusae I have light, though large format, CCD. I have faffed about with the adjusters till I'm blue in the face and I would rather have a focuser that worked. However, WO have never been terribly good at providing them! It would help if they made their tubes the right length to start with instead of hanging half a ton of gear off the back of an over extended draw tube. WO get ten out of ten for prettiness but rather less for functionality, from me at least.

Olly

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The two recent fracs I have bought have lovely R&P focusers - The Japanese Vixen ED81S and the Televue Pronto .. both are a Joy to use...

My Megrez 72 on the other hand has a WO "One-way" crayford.. ok racking out with a load on but needs a helping hand to rack it back in....

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my TAL 100rs has a russian built crayford single speed and its a joy to use, and one of the reasons i bought this scope to replace my old evo 120

my st150 has a dual speed skywatcher that i fitted as the R&P was goosed on it

no complaints from me

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Focuser types (R&P, Crayford, Helical) come in and out of fashion. Whilst all have their strengths and weaknesses the determining factor is price. A cheap R&P will be soundly thrashed by a well-made Crayford, and vice-versa.

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Having got a JMI motorised crayford perhaps I'm spoilt. My other scopes have a R&P and a Helical. I'd say my Crayford is best for useability/control/precision but worst for price (>£200 IIRC). The Helical is a pain to focus... but will not shift.. and is so strong when I dropped my scope with it on, landing on the focusser, the ally tube buckled, but the focusser survived, and it was relatively cheap (£70). My R&P is on my Tal-1M, and is good to use for visual stuff there is a touch of slop and rotation etc. but for a cheap focusser on a £200 scope it's excellent.

It's the age old problem.

Top ranked stuff gets a new gizmo.. it's really really good and solves a lot of problems/really nice to have.

Attempts are made to replicate on cheaper made stuff and it just doesn't work.

So with scopes as with anything else:

buy less.. buy quality.. buy once.

Derek

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ok, so instead of bemoaning the poor design, what would be a perfect design for a telescope focuser? im guessing a rack and pinion made to a high tolerence maybe with roller bearings to support the draw tube?

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Even worse than the debate over R & P v Crayford (although recent experience has shown me the path to true enlightenment!) is that even my Feathertouch R & P didn't come with a manual, there are no instructions on-line and yet there are clearly adjustments in various places but no info on what they do!

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gotta love a feathertouch!!!

Im not enamoured over the price though. They are very classy

As im after motorised focuser's ironically most of the nice frills are pointless. (not referring to motorised feathtouch as they are well out of my league atm)

Im looking at a Baader Steeltrack as my next focuser upgrade with the motorised option. The Belt drive Steeldrive appeals more than some other options out there especially if I can swap it to other scopes easily. Im awaiting details.

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I can do if you like! Our TEC has one. The review won't take long; it's perfect. It is firm to move but decisive and you can make miniscule ammendments to the FWHM. It holds all night and never slips. I feel it deserves a bit more than perfect really but how do you do that?? The two speed Tak is also near perfect on my scope but the French mag did find theirs created some image shift when moved. Mine doesn't though. However, I'd dock it half a point for the fact that the camera rotator can move with a lurch the first time you use it after a while in the same place. The rotator on the TEC is a massive thing - the entire focuser in fact - and is as smooth as you like.

Olly

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Steel on steel is good enough for railways and fine in a focuser for me, as is steel on anodised aluminium. However steel on paint destroys the paint and so the tube on my refractor looks decidedly careworn.

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Steel on steel is good enough for railways

As engineering problems go though, locomotive wheels and telescope focusers are pretty much opposite ends of the spectrum, aren't they? Granted they're both about traction, but the use cases are very different and what works at one scale and level of power may be completely inappropriate for another.

James

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I agree Olly, I have recently been looking at FLT98 and just couldnt bring myself to go for one with the DDG because of my past experiences with crayfords, I just think (maybe wrongly that its a bit gimmicky). I waited and got a nice FLT98 with R&P Feathertouch , its just so much better and takes all the weight I can throw at it and its still smoooooth.

The only crayford I can put up with is the moonlite which I have on my 127EDT, its a lovely piece of kit and works properly. Just shows what a crayford can be like if its not built to a budget.

Philj

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As I understand it the Crayford focuser was originally a DIY design that would be easy to build and because it followed reasonable kinematic design principles did not require any high accuracy in its construction to get a smooth focusing action.

There are some very good examples in the market place and obviously some poor ones. Its main weakness is that any load has to be taken by the rolling friction of the bar on the focuser tube and I know of one manufacturer who added a spring that could be attached when the load was vertical. This is not an issue with “screw” based focusers as they normally automatically lock against the screw. However, they require accurate machining and consideration of how the focuser tube is supported.

In some ways the best design of all is potentially one based on a compliant mechanism and one manufacturer does produce one (Clement) but they are expensive.

As to railways and focusers the scaling is actually ok as the force required scales linearly with masses involved.

Andrew

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Sure but the ZS66 focuser hasn't a hope in hell of holding big CCD gear. This is well known.

Olly, let's put this in perspective. The ZS66 sold for £239 for the complete telescope: body, optic and focuser. The Feathertouch R&P focuser alone typically costs over £400...

It would help if they made their tubes the right length to start with instead of hanging half a ton of gear off the back of an over extended draw tube. WO get ten out of ten for prettiness but rather less for functionality, from me at least.
The tubes are the correct length for most observers. For imagers using their FLT telescopes WO offer an extension tube (think of it as a body extension tube, not a focus extender) which reduces the required drawtube extension. That is definitely the case for the FLT-110 and FLT-132, possibly others too (I'll check).

I do however agree some of the WO DDG focusers could and should have been better. WO are currently changing their focusers, you will be pleased to hear the new ones will be based on the R&P design.

As I understand it the Crayford focuser was originally a DIY design that would be easy to build and because it followed reasonable kinematic design principles did not require any high accuracy in its construction to get a smooth focusing action.

You have hit the nail on the head Andrew. The Crayford was designed to enable a smoothness and precision that was not possible with R&P focusers, at least not at the same price. At the budget/intermediate end of the market Crayfords rule, and rightly so!

R&P focusers can be made to a very high standard. Olly's favoured Feathertouch at £400+ is perhaps the best example but not everyone is prepared to pay that much.

I put it to you that the metal on metal Crayford is an aberration and we, the customers, should be saying NO the things and sending them back until the makers get the message that we don't want them.
The majority of astronomers on regular incomes find Crayford focusers serve their purpose well, at the price they want to pay. (My own Baader Steeltrack Crayford focuser is carrying an Atik 314L, Titan, EFW2 motorized filter wheel and off-axis-guider without difficulty).

HTH,

Steve

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