Esprit 120 fine focus knob slipping (and Sesto Senso autofocuser as well)

[rofus]

2 hours ago, inFINNity Deck said:

I had exactly the same issue with my Esprit 150ED and solved it in two ways: first I replaced the 1:10 friction type planetary drive for a home-made 1:16 geared one. Once that was done I created a special tool to open the friction version, cleaned and re-greased it and tightened it until it had enough friction to work again. I now use the friction planetary drive for the rare times that I am visual observing with the scope and the geared one for imaging. The friction one now easily holds my 2" diagonal with the heaviest eyepieces I have, which are around 1.2kg.

More info and pictures on my website.

Nicolàs

Hi Nicolas

 

very nice and informative indeed! That confirms my suspects and what everyone said. Problem is that I don’t have the knowledge or manual ability or confidence to do anything near what you did..

BUT I’ll keep it in mind in case I find someone in East Anglia able to do that :D

[SimM]

On 29/11/2020 at 23:51, rofus said:

I installed the SESTO SENSO  robotic and is working, although if I do a full run inward and outward of the focuser, it doesn't return precisely to 0, so along the line the position shifts a very little bit, but in normal use (movements are much smaller) it works.

I think you have to define "work". Yes, it travels up and down, but using it with presets doesn't work reliably. At anything close to pointing at the zenith, you won't get the exact number of steps (translated into movement "steps" of the focuser). I sent the SESTO SENSO back because it couldn’t limit slip of the OTA focuser (which is far from ideal with a camera attached).

Edited December 14, 2020 by SimM

[rofus]

That was a long post! 🙂 I suppose you were disappointed by the Sesto Senso, and I understand. Actually I have also an EAF that I use on another scope, so I could easily swap them and use the EAF (very similar to Pegasus Cube) on the Esprit. And I do love Pegasus stuff as I have as well their rotator and dc hub!

Personally, if I had to choose, I'd say it makes more sense to use the reduction gears in the scope without reinventing the wheel, but it seems is not so easy.

My one works meaning that even at zenith it doesn't move, it actually holds (not sure why in your case it resets). I've done curves in Voyager and I get reliable focus like I get with the EAF on the other scope, but surely is annoying to know it might loose some step here and there and so it might work even better.

I mounted a few autofocusers with plate, I really don't like it, is not a stable connection for me. And not all of them give clear instructions. Speaking with Skywatcher directly, some of the screws that Pegasus says to use, SW says to not use them (by that I mean not the way Pegasus says). With EAF is even worse, as ZWO says they don't have a specific adapter for Esprits and you need to be 'creative' 🙂

Anyway, I'd still like to have the microfocuser to work properly, even without using it for autofocusing. The design of Senso (no mounting plate) is definitely more advanced for me, but it probably works at 95% precision instead of 100%, and I'm ok with it at the moment, even if I want to try and do more to make it better if I can...or maybe change to the EAF or Pegasus who knows...but I don't want to give up yet.

Hopefully @inFINNity Deck solution can help. Problem here is not the Sesto Senso, but the Esprits focuser, so let's see if I can make it better. Sesto Senso will work as precisely as the microfocuser is, so is still something I want to explore.

[SimM]

-

Edited December 10, 2020 by SimM

[SimM]

-

Edited December 10, 2020 by SimM

[SimM]

-

Edited December 10, 2020 by SimM

[SimM]

On 21/11/2020 at 01:51, rofus said:

Actually I found a video showing exactly the problem:

 

In the video, the micro focus knob doesn't move the focuser rack and one factor may be the the screw under the 11:1 mini/micro focuser being loose.

Edited December 14, 2020 by SimM

[johnturley]

On 21/11/2020 at 15:29, johnturley said:

Dave

Do you know what size Allen key fits this bolt, I have similar problems with the fine focuser on my Esprit 150

I've tightened very slightly the 2 bolts either side of the focuser as shown in the in the photograph below with a 2mm Allen key, to prevent the focuser from slipping, however if you tighten them too much then the fine focuser won't work. You also have to be careful not to slacken them off too much, otherwise I understand that there is a risk that the pressure pads can fall out, which are very difficult to replace.

John 

Checked on the size of Allen key required to tighten the bolt under the focuser and its 2 mm (same size as the 2 bolts on either side of the focuser), and tightened it slightly, plus tweaked the bolts on the focuser tube to reduce/prevent slippage of the focuser when the scope is in a near vertical position. I find that the latter gradually loosen over a period of time.  

Its not that bad a focuser on Esprits, certainly a lot better and more solid than those on Explore Scientific Refractors, the main problems being that they are fiddly to adjust (originally the heads of the bolts on the focuser tube on mine appeared to be made up with glue), and lack of any information in the manual about how to adjust them. Its a pity that they don't have knurled headed adjustment knobs like on the ES Refractors.

I can agree though that if you want to use an electronic focuser, then some upgrade to the focusing mechanism may be required.

John  

Edited December 1, 2020 by johnturley

[inFINNity Deck]

16 hours ago, SimM said:

In the video, the micro/min focuser is slipping so the focuser doesn't move up to overcome gravity.

The solution is to tighten the screw under the mini/micro focuser (the closest screw to the pair of knobs).

 

In my Esprit 150ED those screws have nothing to do with how the 1:10 drive works and how it grips the 1:1 axis. If you check the images on my website, you will see that the 1:10 knob is mounted on a thin shaft, which sits between 3 bearing balls. These three balls are wedged between that thin shaft and the conic outside of the outer stainless steel bushing. Pressure is increased by rotating clockwise the brass ring-nut (which pulls the central 3-hole hub), but you will need a special tool for that (and first get rid of the lock-tite kind of sealing). Care should be taken not to apply too much pressure as that may create dents in the central shaft.

Care should also be taken when dismantling as there are 18 tiny bearing balls below that ring-nut, which will wander off in 18 directions.... 😉 So make sure you work over a tray to catch them balls.

I have serviced mine and now it easily holds a diagonal and a TeleVue Ethos 21mm or PanOptic 41mm, both weighing about 1.2kg.

Nicolàs

[marcus_z]

Hi,

in case you would like to change the focuser to a 3" Feather Touch: I am offering the matching adapter and endcap for the 3" FTF in the classifieds section of this forum.

Cheers,

Marcus

[david_taurus83]

I'm guessing I also have this same issue. Fine focus still works but slight pressure on the drawtube and it slips if I adjust coarse focus. I thought it was the fine focus knob itself slipping on the round shaft so I ground a flat surface on one side but even then the shaft stays stationary while course will turn.

 

[david_taurus83]

Just reading @inFINNity Deck website there and it's very disappointing to see how they have designed the fine focus control. On one hand we have a good sturdy rack and pinion system for the course focus but essentially a crayford type friction system on the fine focus and not easy to adjust either. Very poor on a scope designed for imaging.

[Oxize]

Is this to much shift? Or is it normal (5x digital zoom on DSLR).

 

Edited April 20, 2023 by Oxize

[johnturley]

10 hours ago, Oxize said:

Is this to much shift? Or is it normal (5x digital zoom on DSLR).

 

Unfortunately I do not think that the stock focusers on the Esprits are up to coping with heavy accessories such as a digital SLR, on the other hand I do not find much of a problem with my ZWO ASI 462 camera mounted on my Esprit 150 with the stock focuser.

John