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Motofocusers- which one?

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#1 aneeg

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Posted 16 July 2019 - 02:56 PM

I am in the market for a focuser upgrade. I want one that I also can use manually so there will be no need to disengage the motor.

Does such a focuser excist?

 

Arne



#2 descott12

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Posted 16 July 2019 - 03:32 PM

I use the JMI motofocus sold by farpointastro. They are definitely low-end but they work and they are only $199. They sell different models for most focusers. The nice thing about them is there is a windows app to control them and a hand controller that you can keep scope side or run remotely via a long audio cable.

 

The downside is they are not ASCOM compliant as far as I know and the quality is not great. But I like them because they are inexpensive and they do the job. You definitely do not want to manually adjust the focuser while it is installed (I damaged my last one that way) but if you use the hand controller scope-side you are good to go.  You probably want to use the hand controller anyway to keep from shaking the rig.



#3 t-ara-fan

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Posted 16 July 2019 - 04:04 PM

I have a couple of Moonlite focusers - on my refractor and EdgeHD-8.  They are expensive, but they are BEAUTIFUL and work very well. 

 

You just twist a shaft to engage/disengage them. I often to do a manual rough focus, then tighten things up and Autofocus.  They come with a USB controller that is ASCOM compliant so it works with any focus control software.  The controller also lets you manually focus by pushing buttons to turn the stepper but I just twist the knobs.

 

For a year or two I just focused from my computer using FWHM/HFR tools.  And I was happy with that.  Then I finally tried autofocus in SGP. It worked the first time.


Edited by t-ara-fan, 16 July 2019 - 06:24 PM.

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#4 RaulTheRat

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Posted 16 July 2019 - 04:09 PM

I am in the market for a focuser upgrade. I want one that I also can use manually so there will be no need to disengage the motor.
Does such a focuser excist?

Arne

The baader steeltrack and the steeldrive ii motor kit will do this. One of the few that will, and on the baader because there's no reduction gearbox the focuser action is actually quite usable even though the motor still remains connected to the focuser knobs. It's definitely notchy and much less smooth and pleasant to use than it would be if the motor were not fitted, but it is ok and probably about the best you'll find I expect.

Why nobody makes a declutchable focus motor that can be left in place on the shaft but fully declutched for manual use I have no idea, it would not seem that difficult an engineering problem, but I don't think such a thing exists.

Edited by RaulTheRat, 16 July 2019 - 04:10 PM.


#5 aneeg

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Posted 16 July 2019 - 05:46 PM

I know the Moonlites are expensive, but probably I will cry only once.

 

Arne



#6 airydisc

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Posted 17 July 2019 - 01:35 PM

There's a lot of clarification and additional information that might be helpful to this discussion.  First, let's define some terms:  The word "focuser" is typically used to refer to the mechanical part of a telescope that allows you to adjust the focus (whether it is by moving the eyepiece or sensor in and out, or moving a mirror to change the distance).  In most cases it is possible to add a motor ("focus motor") to allow finer control of focus and (perhaps more importantly) do it without touching the telescope.  The focus motor is typically driven by electronics in a separate enclosure, the "focus controller".

 

There are 2 broad categories of focus motors, incremental and absolute positioning.  An incremental positioning focus motor typically has a small DC motor (and gears).  The controller for such a motor is fairly simple, typically giving you buttons for "in" and "out" movement, and sometimes a speed control.  This can be a vast improvement over manual focusing because the reduction gears provide finer control of the position, and because you can do it without inducing vibrations in the telescope by touching it.  However, the position cannot be "predicted" reliably because the movement of the motor will vary with the load and the source voltage.  And, of course, you cannot precisely control how long you are pressing the buttons.  In some cases these controllers can be connected to a computer, where a focus application can more precisely control the timing, but you still have the other issues.  The end result is that accurate auto-focus is generally not possible with this type of motor, so it is most appropriate for visual observing.  In some cases a DC motor controller can be powered by small batteries.

 

Absolute positioning motors use stepper motors (or, in rare cases, servo motors) to precisely control the position of the focuser.  This requires a more sophisticated controller, and they pretty much always have a computer interface to allow auto-focus and remote operation.  In most cases the actual auto-focus operation is done by other applications, since you have to have control of both the focuser and the camera to perform an auto-focus.  Some such controllers provide both the computer interface and "manual" control (through a handset).  In some cases the controller is integrated into the motor enclosure, such as with the ZWO EAF and Prima Luce's Sesto Senso.  Integrating the controller and motor makes sense if you don't need manual control, and already have the computer interface (USB) near the focuser.  For example, many modern cameras have USB hubs built into them, so one of the downstream ports could connect to the focus controller.  But you also need 12VDC power.

 

Here's where it gets messy:  For an absolute positioning focus motor to work correctly the focuser must not slip.  Crayford focusers pretty much always slip - especially after they have been exposed to dirt and oil, etc.  The Moonlite focusers (with the possible exception of their "Nite Crawler" focuser/rotator) are Crayford focusers, so much as I like their design, I can't recommend them for auto-focus operation.  Instead, a rack & pinion mechanism is highly preferred.

 

Next, most focusers on refractors and Newtonian telescopes have "dual speeds", meaning that you have both coarse and fine focus knobs.  The reduction mechanism for the fine focus knob is, in many respects, a great design.  It provides good reduction (usually around 10:1) with smooth operation, and almost no backlash.  So naturally, it would make sense to connect a focus motor to the fine-focus shaft (or knob) to reduce the amount of reduction gearing needed in the motor (reducing both the cost of the motor and the amount of backlash, since the gears in the motor always have backlash).  Unfortunately, in almost all dual-speed focusers this reduction mechanism will slip, and just like the Crayford focuser, this makes it undesirable for absolute position control and auto-focus operation.  I have tested this on focusers from many different manufacturers, and the only one I have found to work reliably is the FeatherTouch line (note that their entry-level 1.25" and 2" focusers are Crayford type, so you need to select the rack & pinion type).

 

With regard to "manual override", both Moonlite and FeatherTouch offer absolute positioning (stepper) focus motors with a mechanism to disengage the motor, allowing manual focus without removing the motor.  In the Moonlite system only coarse focus is possible when the motor is disengaged, while the FeatherTouch allows both coarse and fine focus access (with the "handy stepper motor" HSM).

 

The only other mainstream product I know of that provides manual control without removing the motor is Prima Luce's Sesto Senso.  It uses a very unusual design in which the stepper motor has no reduction gears, but is connected to the fine-focus shaft (it cannot be used on focusers that do not have a fine-focus knob).  To get sufficiently small steps in focusing, the Sesto Senso controller uses "microstepping", a technique that allows the motor to be positioned at a number of points (16 in this case) between full steps.  There are some significant drawbacks to using this technique, but it does allow one interesting and useful feature:  When the motor is turned off there is relatively little load on the focus shaft, so it is possible to turn the coarse focus knob on the other side of the focuser by hand.  It is coarse focus only, and not as smooth as it would be without the motor, but very easy to achieve - you just turn the motor off. 

 

Note that in some focus motors using stepper motors they rely on friction to hold the position after the motor moves.  This is impossible with the Sesto Senso because there is not enough friction.  However, even in systems that use reduction gears (and cannot be turned by hand without disengaging or removing the motor) it is a bad idea for the controller to turn off the motor when it is not moving.  The reason is that even though the friction will hold the focuser in the desired position, the internal "springiness" of the gears will push the motor itself to a different position, so the starting point of the next move is undefined.  This error is generally pretty small, but accumulates with each movement.  Most focus controllers do not even specify whether they use the motor to hold the position while not moving or just let it go.  Their are 2 different kinds of stepper motors, called "unipolar" and "bipolar".  There are only small differences in the performance of one type of motor over the other, but bipolar motors are typically used with a more sophisticated and expensive controller, and one feature of such controllers is that they can reduce the current to the motor while it is not moving, so there is enough to hold the position without consuming a lot of power.  Robofocus, Moonlite, and many other focus motors are unipolar.  The FeatherTouch HSM and PDMS motors are bipolar, and their controllers use this braking technique to maintain absolute position control.

 

OK, I'll admit it:  I'm a big fan of FeatherTouch products.


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#7 denny-o

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Posted 19 July 2019 - 01:31 PM

Hmm, Chuck uses Moonlite. I don't notice any focusing creep in his published photos. Perhaps creep is not a problem with properly engineered equipment.



#8 SteveInNZ

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Posted 19 July 2019 - 04:50 PM

I use the JMI motofocus sold by farpointastro. They are definitely low-end but they work and they are only $199. They sell different models for most focusers. The nice thing about them is there is a windows app to control them and a hand controller that you can keep scope side or run remotely via a long audio cable.

 

The downside is they are not ASCOM compliant as far as I know and the quality is not great. But I like them because they are inexpensive and they do the job. You definitely do not want to manually adjust the focuser while it is installed (I damaged my last one that way) but if you use the hand controller scope-side you are good to go.  You probably want to use the hand controller anyway to keep from shaking the rig.

I don't know if applies to all JMI focusers, but the ones I have use a thumbscrew to engage/disengage the motor by lifting the drive gear. I also believe that you can use Shoestring FCUSB (?) to connect to the simple pushbutton focuser and make it ASCOM.

 

Steve.



#9 bogg

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Posted 19 July 2019 - 06:24 PM

I use a Pegasus Astro focus cube. So far it has worked well, but I am still in a learning curve with astrophotography. 



#10 airydisc

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Posted 20 July 2019 - 12:56 AM

Hmm, Chuck uses Moonlite. I don't notice any focusing creep in his published photos. Perhaps creep is not a problem with properly engineered equipment.

Finished astrophotos don't show how many subs were discarded in the process!  But it's also true that if you know what you are doing, the effects of minor slipping can be avoided - it just takes understanding, and more patience than most people possess.



#11 cmfrommen

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Posted 30 July 2019 - 08:00 AM

I am undecided between the Starlight Instruments SI-EFS---Electronic Focusing System or their Focuser Boss II system. The EFS including HSM30 motor (to fit my AP 2.7" focuser with FT micro) is about 30% cheaper than the Focuser Boss II (incl hand controller and same motor). What I like about both of them is the ability to still operate the focuser manually w/o laptop and with a simple handcontroller.

I still don't understand what added value the focuser Boss II has over the ESF system which justifies the additional 30% in cost. Anyone who has experience with either of these two systems?



#12 scadvice

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Posted 30 July 2019 - 12:03 PM

There's a lot of clarification and additional information that might be helpful to this discussion.  First, let's define some terms:  .............................................................................................................................................................................................................................................................................................................................. The FeatherTouch HSM and PDMS motors are bipolar, and their controllers use this braking technique to maintain absolute position control.

 

OK, I'll admit it:  I'm a big fan of FeatherTouch products.

Very good post airdisc!

 

I'll add to some information. 

 

I understand currently ZWO's don't have backlash compensation so I'd say wait on them for consideration until they do. It's a necessary function offered by most all other manufactures. I know the Pegasus does as I had one. The Pegasus focuser motor unit worked fine but were not compatible with some other upgrading I wanted to do later this year so I moved on to Optec focusers. In comparison to Optec they are less expensive but slower slewing, and their auto temperature compensation is less sophisticated. They use a plastic housings on the stepper body and controller box and there is no method to release the motor.

In defense of Pegasus, they fill the mid range market quite nicely and should be considered if the budget is at that price point. They are also for the most part interchangeable between most brand focusers.

Sesto Senso unit MAY be comparable to Pegasus with a nicer package but I have no direct experience with them.

 

Moonlite's top end focusers I'm told are excellent and very popular but a bit bulky and heavy, more made for bigger systems with larger mounts to carry them.  Their mid range units I know nothing about.

 

The FeatherTouch system was as I understand designed by Optec for the FeatherTouch.

 

If your budget can swing it look at both FeatherTouch and Optec  DirectSync focusers. I have two of the Optec and think they are great. The neat thing about them (Both Optec and FT) is the quick (very quick) disengagement and re-engagement that allows you to hand focus it if necessary even in the dark.  With the history of design between FT and Optec  FT's stats are mostly the same as Optec as I've noted below with some small design differences.

https://www.optecinc.com/

 

Optec motorized units in general I believe are not directly interchangeable without changing the mounting hardware. So you would need to talk to Optec about that possibility. The aluminum makes them a little heaver but also very solidly made. No plastics and the weight added is only a few oz. Most likely this applies also the FT.

The Optec and FT units are both quality top end products that cost more to make thus a few hundred more outlay and IMO definitely worth the extra cost. They both have all machined and anodized aluminum bodies including the control box. They have a release mechanism that allows you to hand focus at anytime and other optional things such as WiFi, replaceable control boards, adding of a second focuser board and were made for the option of using remotely if desired. The controls are version upgradable over the internet.

 

So it looks like both airydisc and I agree that the FeatherTouch and Optec focusers are excellent options. 


Edited by scadvice, 30 July 2019 - 12:12 PM.

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#13 airydisc

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Posted 06 August 2019 - 01:27 PM

The FeatherTouch system was as I understand designed by Optec for the FeatherTouch.

 

If your budget can swing it look at both FeatherTouch and Optec  DirectSync focusers. I have two of the Optec and think they are great. The neat thing about them (Both Optec and FT) is the quick (very quick) disengagement and re-engagement that allows you to hand focus it if necessary even in the dark.  With the history of design between FT and Optec  FT's stats are mostly the same as Optec as I've noted below with some small design differences.

https://www.optecinc.com/

 

Optec motorized units in general I believe are not directly interchangeable without changing the mounting hardware. So you would need to talk to Optec about that possibility. The aluminum makes them a little heaver but also very solidly made. No plastics and the weight added is only a few oz. Most likely this applies also the FT.

The Optec and FT units are both quality top end products that cost more to make thus a few hundred more outlay and IMO definitely worth the extra cost. They both have all machined and anodized aluminum bodies including the control box. They have a release mechanism that allows you to hand focus at anytime and other optional things such as WiFi, replaceable control boards, adding of a second focuser board and were made for the option of using remotely if desired. The controls are version upgradable over the internet.

 

So it looks like both airydisc and I agree that the FeatherTouch and Optec focusers are excellent options. 

Thanks for the comments, scadvice.  I will add that FT now has a newer focus controller at a lower price point, the "EFS" or Electronic Focusing System.  It has similar functionality to the FB II (the one from Optec), but does not offer all the optional upgrades such as a second focus channel, or wi-fi.  It is not from Optec.  A good User Manual is available from their website:

 

http://starlightinst...&product_id=475



#14 descott12

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Posted 06 August 2019 - 01:42 PM

ZWO also has their new EAF which looks quite good. Backordered now but the quality looks great.




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