TS monorail focuser woes

[Clarkey]

I recently purchased a TS 6" F4 Photon newtonian specifically for imaging. I knew there were a number of potential difficulties on purchasing, not least the need for excellent collimation and the need for a good coma corrector. (I did try a Baader MPCC I already had, but it did not give good results so I got a SW Aplanatic which gives good stars). Unfortunately the focuser also seems to be worse than I was hoping. I have managed to get it aligned with some shims, but it will not work accurately with the electronic focuser. If I tension it enough it does not slip, but some small adjustments of focus just 'bounce' back to the original position. Having looked at the internals I am not really surprised. There is loads of play in the focus axle, probably due to the lack of bearings and a plastic housing. Additional the drive is so thin it bends under compression. In reality, what could be a really good focuser is let down by some penny pinching on a thicker piece of steel and a couple of bearings. Given it is sold as an imaging scope it is a bit of a let down really.

What I would like to know is whether there are any 'tricks' to improve the operation of these focusers? It is sold by TS as an improvement over the standard Crayford focusers, but in my opinion it is worse. As it is largely plastic I feel a bit limited in terms of an 'engineering' solution.

Any hints or suggestions would be appreciated.

[vlaiv]

I had that focuser on my RC - and my solution was to replace it and get R&P one.

I think that R&P are better option to work with motor/auto focusers.

I'm surprised to hear that newtonian model of this focuser has plastic bits. Mine is all metal (M90 model).

[Captain Scarlet]

I bought that same focuser as an "upgrade" for my then new skymax 180. It was terrible, and your word "bounce" describes it perfectly. The fine-focus wheel just wasn't "direct" at all, bouncy and spongy. I did try some surgery on it, and (long story) by the end a hammer was involved, trying to extract a pin: I effectively destroyed it. I still have all the bits, and even if it were still whole I wouldn't have the conscience to sell it on to anybody, it's so bad.

M

Edit: the Skywatcher/OVL/Revelation (all the same I think) dual-speed Crayfords are much, much better (and cheaper!).

Edited October 17, 2021 by Captain Magenta

[johninderby]

I had one of these on my TS Classical Cassegrain and replaced it with a Baader Steeltrack. Well worth the money for a great focuser. 👍🏻

[ollypenrice]

Like vlaiv, I would go for a rack and pinion.  I host a number of robotic scopes and find that the R and P focusers never give any bother but the Crayfords regularly do so, including reputable ones like Baader and Moonlite. When you're counting steps or supporting a heavy weight against gravity you want more than friction to keep things consistent.

(Yes, I use friction drive mounts but they are in balance, not being tested against significant resistance.)

Why it seems to be so hard to make a focuser is something of a mystery.

Olly

[Clarkey]

Ok, as I suspected a new focuser is in order. I have got the Baader steeltrack on one of my other scopes which has been good, but I'll maybe look at the R&P option (if I can find any available anywhere).

Thanks for the responses.

12 hours ago, vlaiv said:

I had that focuser on my RC - and my solution was to replace it and get R&P one.

The one on my GSO RC8 was way better than the one on the Photon and I changed it to the Steeltrack.

 

1 hour ago, ollypenrice said:

Why it seems to be so hard to make a focuser is something of a mystery

Agreed. I would rather pay a few pounds more for a useable focuser. Alternately, sell the scopes without focusers and reduce the price accordingly.

 

12 hours ago, Captain Magenta said:

Edit: the Skywatcher/OVL/Revelation (all the same I think) dual-speed Crayfords are much, much better (and cheaper!).

Agreed.

[johninderby]

I have never had any problems with the Steeltack. I want the replace the R&P focuser on one of my scopes with a Steeltrack as it simply doesn’t work as well as a Steeltrack so R&Ps aren’t allways better.

Edited October 18, 2021 by johninderby

[vlaiv]

1 minute ago, johninderby said:

I have never had any problems with the Steeltack. I want the replace the R&P focuser on one of my scopes with a Steeltrack as it simply doesn’t work as well as a Steeltrack so R&Ps aren’t allways better.

R&P are still better option for motor focusers.

This is because motor focuser will hold the load on focuser with its own holding torque. With crayford style focuser, there is point where slippage can happen even if holding torque of motor focuser is not exceeded. With R&P - it is effectively a geared connection between motor focuser and focus position and you really need to move motor shaft in order to change focus (and vice verse).

For that reason - motor focusers work better with R&P focuser - but that does not mean that there aren't better crayfords out there than some R&P.

[Clarkey]

FWIW I have just ordered a Steeltrack from FLO. I had a look for R&P focusers as I can certainly see the benefits as although there might be a bit of backlash it won't drift. However, there seems to be a European shortage of suitable options at the moment. The Steeltrack on my RC8 has been excellent, so I am happy that the newtonian version will perform equally well.