Primalucelab-Sesto-Senso Auto Focuser

[teoria_del_big_bang]

NOTE: This review is only my assessment of this piece of kit, I only have used one other auto-focuser before (which worked brilliantly) but means I cannot compare it a myriad of other similar devices and am not claiming this is better or worse than them as I cannot.

I have just fit one of these to my Esprit 100ED. The main reasons I chose this over others were:

• Looked a very neat solution with probably the smallest footprint of all focussers as far as I could see (I guess similar to ZWO EAF focuser but without the addition of a bracket), mainly due to the direct connection and not requiring a timing belt and the way it attaches onto the collar and thus does not require a bracket.
• Price was very reasonable at £259, so about in the mid price range for this type of device.
• A well know and what seems to be a good manufacturer.
• I do not think a hand help controller is available for this unit but I did not require one as it would all be done through APT or similar.

• I was very impressed with the fact everything is included in the box in order to fit and use the auto-focuser on most popular focusers.
  • Auto-Focuser
  • 5 couplings to fit the most popular focussers, all grub screws (+ a fair sew spares as they are impossible to find one dropped) + the two allen keys required
    • Red bushing Ø2.5mm for AIRY refractors (ED72, APO80, ED90, ED100, APO104T, APO120, APO150T), OrionOpticsUK VX and CT, Baader Steeltrack® focusers, TS-Optics V-Power,Omegon V-Power and Skywatcher
    • Black bushing Ø2.8mm for Feather Touch focusers
    • Green bushing Ø3.5mm for Takahashi telescopes
    • Silver bushing Ø3.1mm for Moonlite focusers
    • Yellow bushing Ø4.0mm for AIRY refractors (APO 65F, BLACK 80T) and SharpStar telescopes with 2" focusers
  • Power cable with cigarette style 12V plug.
  • Usb cable to connect to computer
  • All software on USB stick (Application, drivers for focuser, ASCOM drivers 32 & 64 bit, manual)
• The unit requires that you have to take off the rough and fine focussing knobs which on the Esprit was very easy.
• For myself the fitting was very straight forward, I have heard of issues with alignment from other users so maybe I was lucky and I can easily see how there can be alignment issues. Because the coupling is solid the alignments need to be pretty accurate. Any misalignment risks damaging wither the focuser or the auto focuser, although damage is probably unlikely but what will definitely happen is the focuser will bind meaning it will not run smooth and maybe difficult to obtain accurate focus.
• The software looks pretty good and set up and calibration is very easy.
• 32 & 64 bit ASCOM drivers provided as you seem to need the 32 bit driver for APT to work even if you have 64 bit Windows.

I did have an initial issue with alignment and binding but was down to me not reading instructions (at all).

The idea is simple as supplied are 5 couplings all with one bore to fit the motor shaft and the other bores various diameters designed to fit popular focusers. Also provided with the couplers were around 8 small grub screws. You need 2 to tighten the coupling to the shaft, the others some of the others I assumed were to fit into tapped holes around the collar (there are 3 tapped holes that fit the grub screws and I assumed this was to aid alignment and that they were to be used as jacking screws, that are used to align the two shafts in the coupling, together with the bigger screw to tighten the collar on the boss of the focuser.

But using these grub screws caused the two shafts to be offset. Any slight offset and you can tell as when you manually use the focuser you can feel it go tight once per rev.  When I removed the grub screws and just tightened the main screw , as the instructions tell you, it all seemed to align perfectly.

When I actually read the instructions the three extra grub screws are only required for certain focusers where the focuser collar size is smaller than the inner diameter of the sesto-senso and are used to retain an adapter bush (a bush not required for the 100ED so not sure what they look like but assume some sort of split ring). 

Now whether not all collars even on focussers that supposedly do not require this bush are exactly the same diameter for differing manufacturers or not but I guess they would only need to me fractions of a millimeter different to start causing some issues as the split collar on the sesto-senso will not clamp in same radial position for differing diameters. And how easy alignment is if you have to buy an adapter bush again I cannot comment but comments on other threads of users seems to suggest not all align as easily and it has been commented that alignment can take several attempts and some time before the action is smooth and there is no binding.

To check it is smooth is really a manual thing in that when fitted and no current is flowing in the motor you can wind the focuser fully in and out by hand, using the one remaining knob, and it is smooth without any tight spots. Yes it is a little stiffer due to the stepper motor residual magnetism but this should be consistent for the whole stroke of the focuser.

I think maybe I was lucky and the collar on the 100ED is band on size. I think the omission in providing flexible couplings instead of solid ones is a big shame and probably lets down what looks otherwise to be a very neat auto focuser. Even if you had to buy the flexible couplings seperate or just state which size you require to fit your focuser. I think one big improvement would be the addition these:-

These flexible couplings allow for some small misalignment without causing a problem. The flexibility though is just in the up-down and side to side movement not radially. Radially they are stiff and so cause no loss of rotary motion.

SUMMARY:

PROS:-

• Small footprint, probably the neatest of all auto-focussers
• No need to buy specialised bracket and find some available threaded holes which to attach the bracket to
• Everything provided for a lot of popular focusers in the box
• All software on usb memory stick makes installation easier
• Nice easy to use software application and easy to calibrate
• Looks very neat. Not sat up above or below the scope with timing belt in between
• I thought price was reasonable at £259 - not the cheapest but certainly not the most expensive.

CONS:-

• Although I did not see an issue many report being difficult to align without causing focuser to bind. Provision of flexible couplings would alleviate this issue as it accounts for some small misalignment. 
• The temperature probe is a seperate item and if bought from same manufacturer is a ridiculous £41. I already had a sensor I bought from DeepSkyDad with my other focuser and so far seems to work perfectly well. This cost 15 euros but not sure if sold separately by DeepSkyDad
• does mean the removal of the manual fine focusing knob so manually only the rough focussing is available.

 

So far I have not had the clear skies to use it in anger, if the review is not locked then I will update it when I have something to report.

 

Steve

Edited October 10, 2019 by teoria_del_big_bang

[baggywrinkle]

Nice report. I have been considering their 2" focuser if it would work on a 12" Meade SCT.

[Jkulin]

I looked at this but chose the Pegasus focuser for just £100 from AA, as it plugs direct into the UPB and works very similarly.

[RMercken]

On 31/10/2019 at 23:08, Jkulin said:

I looked at this but chose the Pegasus focuser for just £100 from AA, as it plugs direct into the UPB and works very similarly.

Is it just `£ 100 or is there extra equipment you need, i was thinking for newest model, not cheap but better and no fuss....

[Adam J]

On 31/10/2019 at 22:08, Jkulin said:

I looked at this but chose the Pegasus focuser for just £100 from AA, as it plugs direct into the UPB and works very similarly.

Its more than 100 pounds, easy to get confused between the focus cube and the motor controller. 

[Jkulin]

Hi Adam, I went for the motor focus kit for £95 (just checked my receipts) as I already had the Pegasus UPB or I could have used a number of controllers that I have that I don't use as the UPB dispenses with that anyway: -

https://pegasusastro.com/motor-focus-kit/

I thought the Primalucelab-Sesto-Senso Auto Focuser was similar in that you still needed a controller for it or does it do away with that completely and just uses a USB connection direct to the computer?

[Dr_Ju_ju]

On 10/10/2019 at 09:37, teoria_del_big_bang said:

I think the omission in providing flexible couplings instead of solid ones is a big shame

I beg to differ, as I've tried both types of couplers on my focusers and found the solid ones to be far superior.

They are thinner, so are easier to mount without fouling\rubbing the sides of the main focuser assembly, especially if the central rod (Crayford's) is not correctly configured.

The mounting grub screws are opposite each other as opposed to a 90 degree offset which can also offset the whole coupler. And being 'flexible' means there can sometimes be induced backlash in the rotational movement.

 

 

[stash_old]

1 hour ago, Dr_Ju_ju said:

And being 'flexible' means there can sometimes be induced backlash in the rotational movement.

True on initial movement perhaps except the flexible couplers act as a "spring" and seem to always return to the "normal position" as the torque reduces and so no induced backlash seems to occur in my experience - could be wrong as no real tests done.  But agree on the grub screw alignment - always in the wrong place LOL.

But the biggest advantage ,especially for the average DIY , is alignment does not have to be 100%  - so out  ways the very small possibility of "induced backlash" IMHO.

[teoria_del_big_bang]

I know I am talking small flexible couplings here but I have worked in Engineering for over 40 years that use flexible couplings and some small enough to suffice for this application. The flexibility it up/down and left to right, there is no rotational flex at all. We work to under 2 micron precision for size and for angle +/- 0.01 degrees so if we use these for our absolute encoder feedback in the loop of our servos there can be no angular error.

I agree some alteration to the design to account for the bigger diameter coupling would be necessary but stand by the fact they would still be an improvement. 

Steve