Focuser Alternatives

       

Subject: Best Focuser Recommendations    

From: Chris Margaritis <vulcanakamail.com> Date: March, 2000

The best electronic focuser would be the Van Slyke: <http://www.observatory.org/scf.htm>

It's heavy and expensive, but has the finest movement and longest travel.

The best for the price is (okay, second best, but more popular among LX200 users) is the JMI NGFS:
    <http://www.jimsmobile.com/ngf_data.htm#NGF-S>

Subject: Focusers Compared--JMI, Optec, VanSlyke    

From: Doc G, Date: May, 2000

Andrew Jackson wrote:

> Thank you for buying one of those and letting us know about it. I saw the
> Optec Focuser advertised a while back and mentioned to the Group as I had
> no way of getting to see one myself. It sounds good. I believe it is cheaper
> that the Van Slyke but more expensive than the JMI. NGF-S with DRO.

The three focusers you mention are in order the JMI at about $500, the Optec at $740 and the VanSlyke at about $1750.

There are very significant technical difference as well.

The JMI is controlled with a hand keypad only. The Optec has a hand keypad and thermal control and computer capability. I do not know about the Van Slyke since I have never studied it in detail. It is large and heavy and probably not suitable for typical amateur telescopes I believe.

> If you don't mind answering some questions:
> Is it worth more than the JMI in your opinion ?

I have not yet tested the thermal part, but I believe that the mechanical quality, which still cheers me to look at, is definitely superior. The fact that there is provision for computer control is also a fine feature. The prices are close enough that I would go with the Optec.

> The only thing I was concerned about not being operate it
> without electronics. Can you do that?

You operate it with a hand keypad just like the JMI. It has computer inputs but they do not provide the interface. Some interfaces are in the works.

> Does it come with a larger aperture adapter to get the largest
> image circle, like the $45 JMI adapter.

Indeed it does. They have even a slightly larger adapter ring than the JMI for about $50. It also fits on the back of their slider focuser. (For 2" filters.) The latter, interestingly also takes the JMI directly.

Subject: Building Your Own Electric Focusser --part 1 of 2  

From: Scott Oates <SOates4616aol.com> Date: Apr 2003

I've built stepper control focusers from their parallel controller board (A100SMC) and the geared steppers (NEMA23DSM) for remote focusing. It works pretty well. If you need additional info you can contact me off line. BTW, I have no affiliation with stepper control. See the following link:
   <http://www.steppercontrol.com/>

-------------------------------------------------------------

Subject: Building Your Own Electric Focusser --part 2 of 2

From: Doug Bennett <db_astroananzi.co.za>

An interesting alternative to stepper motor focus control is a 'servo-focuser'. I'm not sure whether it would suit your requirements, but it's certainly worth a look at:  <http://www.rmss.org/>

Subject: LX200 Focuser Pinouts for Optec TCF Control    

From: Doc G, Date: Nov., 2000

Gerald Miller wrote:
> I have the Optec TCF focuser, and was wondering if I could use the pinouts
> for the focuser from the LX200 panel. Does anyone have the schematic for the
> pinouts on the panel? If not, has anyone coded/scripted a focuser control
> for the Optec TCF?

I have worked with the control of the Optec focuser quite extensively. You cannot use the DC signals from the LX control panel to run the TCF.

This is not quite correct. I have a schematic of a home built unit that converts the DC signals from the LX control panel. It uses a detector circuit and a basic stamp to generate the required signals. I did not develop this device and have not tried it.

The TCF must be run as follows. You can use the control box of course. I have heard of applications where the cable was extended to 100 feet without a problem.

A second way to run the focuser is with digital control signals from a parallel port on a computer. The control scheme requires three signals with rather precise timing. It is necessary to generate the signals at a parallel port from Visual Basic. But this requires a third party tool to run the parallel port. Microsoft has not at this time provided such a tool.

I do not know of anyone who has developed a program to do this though I have heard a rumor that Cyanogen is considering such a program. Such a program is a considerable amount of work since VB is not well designed to control communications ports without third party tools.

I have personally worked with a development version of the Optec control box that has serial control capability. I have written several VB control panels that work very well with this new control box. To the best of my knowledge this box will be available some time but I do not know the production/release schedule that Optec has in mind. This new control box is excellent and relatively easy to program through a serial port. VB does have a serial communications tool that works well.

So there are several options available or on the way. Mechanically the TCF is excellent and the temperature control works very well.

Subject: PC-Controlled Focusing with Optec TC-Focuser     

From: Doc G, Date: Jan., 2001

I have been working with a prototype of the Robo Focus for some months. It is an excellent unit with a good PC control panel. I have also been working on software control panels for the Optec TCF-S. It is not appropriate to compare the Robo Focus to the Optec at this time since they are quite different.

The Optec TCF-S is a short throw Crayford focuser much like the JMI focuser, but much stronger. It has a control box, thermal sensor, thermal compensating firmware and a serial port for control from a PC.

The Robo Focus is a control box with serial control from a PC and with a motor that can be mounted on a standard CAS focus knob or on a standard Crayford focuser.

Thus the Robo Focus is for those who already have a Crayford type focuser with a knob that you turn to focus. The Robo Focus turns this knob with a stepper motor under control of the control box and or a PC control panel. Additionally, it mounts directly on a CAS which has a focus knob that you turn.

I have personally used the Robo Focus on a CAS, LX200, ant it gives extremely stable focus control. It is designed with a backlash scheme that allows for focus in the same direction every time. This is an excellent feature which enables dead on focusing every time in my experience. I can recommend the Robo Focus without reservation. At the same time, I can recommend the Optec TCF without reservation as well. The units are simply different and each will fill an appropriate need.

My personal preference is for a Crayford type focuser. Thus I have used the Optec. On the other hand, I also like the JMI focuser very much. I had three of them, two on LX telescopes and one to play with for motor modification for digital control. I used these with the mirror locked and the JMI for fine focus.

I have converted two of the JMI units to use a stepper motor in place of the DC motor that is supplied. I then drive the stepper motor with the Robo Focus control box. Thus I have a JMI focuser with a Robo Focus controller. An ideal situation in my opinion.

The Robo Focus is very versatile in that it can be made to fit any Rack and Pinion focuser and thus is adaptable to refractors, Newtonians and the like. The Optec is designed to fit the back of a CAS.

Both focusers have open control protocols and can be driven by custom software programs. I use Visual Basic. A friction driven focuser can slip if stressed too hard. I have not had this problem. The Optec is stronger than the JMI in this respect. A rack and pinion focuser will not slip easily.

I do not know the details of software programs being provided for these units at this time. It is my understanding that Cyanogen is considering supplying software for these units as well but I cannot confirm this at present. There is certainly the possibility of having an auto focus program. This would be a very nice feature.

If the Optec is a bit expensive for you, I would highly recommend you try the Robo Focus. It stabilized the focus operation of the LX scope considerably so you may find it a complete solution for your remote control focusing application. It should be possible to apply a temperature control scheme to the Robo Focus as well.

Subject: PCFocus and FocusAide    

From: Roger Hamlett <ttelmahntlworld.com> Date: Jan 2002

----- Original Message -----
From: <joaquin.garzonmcx.es>
> This new autofocus system looks like a godsend for CCD work:
> <http://www.astrovid.com/>
> Any real world experience with an LX200? Does it work?

It has it's own 'Yahoo' group, and some posts are appearing there. It works.

Provided you have a suitable 'absolute' focussing system, you only need the 'FocusAide' software (I have the RoboFocus hardware). PCFocus is needed if you have something like the NGF-S, to create the 'absolute' behavior.

----- Original Message -----
From: Peter Bruce <peterbruceblueyonder.co.uk>
> WOW. -- Look at the price.
> Two holes in a ring of cardboard -- may take longer but you get there.
> You can go on holiday with what you saved.

Unfortunately for focussing on a CCD, this does not work very well. I have wasted whole nights, trying to get really good focus, with Hartman masks (holes in a disk), rods to encourage diffraction spikes, etc. etc...

> Not saying that this aid is no good, OK if you have money to burn.

If you already have a focuser like a RoboFocus, you only need the software. Since you are going to need an electric focuser anyway for this type of work, the extra cost is not that bad. Let's put it this way, getting _good_ focus, is a war with CCDs. I have tried a normal electric focuser, A NGF-S, and a RoboFocus, and the total cost on the way, makes this package look cheap.

Subject: Connecting FocusMax   

From: Mike Valentine <OhioFlyeraol.com> Date: Jan 2003

Clifford Peterson <cpetersonweber.edu> wrote:
I currently run two laptops with my classic LX200. One has MaxIm DL CCD for controlling the 416 via the SCSI adapter. The other runs The_Sky for telescope control using COM 1. I have downloaded FocusMax and it also wants a serial connection to the scope. Has anyone run a similar setup and if so how have you solved the apparent conflict between The Sky and FocusMax?

Answer: I got a dual serial port card from Qualtech (sp?) and it works great. I run The_Sky off the laptops serial connection (com 1) and FocusMax connects thru the card slot. When you set up FocusMax it gives you a choice of com port #'s to use.

Subject: Advice on RoboFocus & FocusMax --part 1 of 3   

From: Matt Thomas <mattstevet.net> Date: June 2004

Matt Thomas wrote:
> Have any of you run a RoboFocus on a LX200 Classic? I'm wondering a few
> things about it. My 8 inch LX200 classic is my imaging scope, and I
> occasionally use it for a grab and go in place of my 18" Dob. I'm
> interested in the RoboFocus to use in conjunction with @focus in CCDSoft.
> If I use the scope for viewing sessions, can I manually turn the focus
> knob while the RoboFocus is installed? Or does the belt have to be
> disconnected to manually turn the knob by hand? Is it clutched? I
> understand that if I were to disconnect the belt, I would have to
> retrain the Robofocus again. So, does the RoboFocus perform well for
> visual applications using the push buttons? Your opinions please...

Doug, I use RoboFocus on my 10" LX200 classic. First let me suggest FocusMax over @focus. FocusMax is excellent for automatic focusing and beats everything else out there. In addition it is free: <http://www.focusmax.org>

There is no clutch with the RoboFocus unit. I believe you could possibly rig a clutch up, but it does not come with one.

Depending on how you set it up, it can be difficult to switch from imaging to visual. Usually the focus position changes quite a bit, and the RoboFocus takes a while for large focus position changes. Once at the visual focus point, it is quite easy to adjust using the control box.

If you do use @focus and you disconnect the belt to use the focuser manually, you really don't need to retrain RoboFocus. The only thing you train it for is to set the ends of focus. As long as you keep the minimum and maximum settings within the maximum focus travel, you shouldn't have to retrain anything when you disconnect the belt.

FocusMax is a bit more complicated then @focus and would require a "retrain" of its own data if you ever disconnected the belt from the focuser.

-----------------------------------------------------

Subject: Advice on RoboFocus & FocusMax --part 2

From: Michael Gerszewski <mgerszewvolcano.space.edu>

Doug David wrote:
> I'm interested in the RoboFocus to use in conjunction with @focus in CCDSoft.

On our 16" LX200, we use a JMI Motofocus on the focus knob for coarse focus and a Robofocus retrofitted onto a JMI NGF-s, and it works great that way for remote control. We use FocusMax as opposed to @Focus, and it works wonders (out of focus to in focus in about 2-3 minutes, hands off). Our 16" has some pretty nasty mirror shift and flop, so we had to go with a crayford style focuser...

> If I use the scope for viewing sessions, can I manually turn the focus
> knob while the RoboFocus is installed? Or does the belt have to be
> disconnected to manually turn the knob by hand?

The main advantage of the Robofocus is that it has a digital stepper motor, so it can be repeatedly repositioned "accurately". I have accurately in quotes because when you deal with a mirror mover, motions aren't always accurate. It may be just as good for you to get something like a JMI Motofocus or other relative analog focuser, especially if you're planning on disconnecting it to manually focus, which will save you a couple hundred dollars. I know the JMI Motofocus controls usually work pretty well, although we don't use it for visual very often.

If you plan on switching between visual and imaging quite a bit, it may be worthwhile to get the RoboFocus, assuming that it is accurate enough using the focus knob. The reason: If you start with imaging and focus, you'll know approximately where focus should be (a count), and when you switch to visual and then back, you could just go back to that count. Although, using an analog focuser might work just as well if a mirror moving RoboFocus isn't extremely accurate.

Now that I've waffled on both sides of the issue, maybe someone whose used the belt-drive unit can chime in.

-----------------------------------------------------

Subject: Advice on RoboFocus & FocusMax --part 3 of 3   

From: Gary Ferdinand <alaparosbellsouth.net>

> Have any of you run a RoboFocus on a LX200 Classic?

It works well on an LX200 classic.

> If I use the scope for viewing sessions, can I manually turn the focus
> knob while the RoboFocus is installed?...

Interesting Q. I believe it to be the case that you can turn the LX200 focus knob manually if the RF is powered OFF. It is not clutched.

As you state, you will then foul up your RF's concept of its current position when you do that. But, if you know what optical setup the RF was last set to, and then reconfigure at the end of the observing night to that same optical setup and refocus, the RF ought to be very close to where you had it in the sense that it will still think it's at 26753 (or whatever it was the last time it was used), even tho you have moved the focus knob manually off that focus point and then back. If you nail the focus on the very same optical configuration you last used the RF on, you *might* be able to get away without any RF recalibration.

As for RF use for visual, yes it performs very well indeed. You use the RF configuration screen to store focus points for various optical configurations and then click on a configuration to tell RF to set the corresponding focus (to eliminate the need for long periods of button-pushing). Then touch it up with the hand control buttons. It works very well that way.

Subject: Focusing Controller Kit -- LazyFocus

From: Doug David <ddavidwideopenwest.com> Date: June 2005

I came across an ad for the LazyFocus focuser controller by James Lacey. It provides a serial port interface to your focuser for autofocusing using FocusMax or other ASCOM compliant focusing routines. It will work in absolute mode with focusers equipped with encoders, or relative mode for focusers without encoders.

I emailed James and asked some questions, mostly if it would work with my JMI NGF-CM (without encoders). Anyway after talking to him about it, it sounded pretty good, so I ordered one. It's a kit, so you need some soldering skills to put it together, but it was easy to assemble. I haven't been able to test it yet due to the clouds, but I assembled the kit in about a half hour and hooked it up to my focuser and it works via the push buttons on the case.

For $90, if it works like he claims, it's quite a bargain compared to say JMI's SmartFocus for $390. I'll be testing it out with FocusMax and MaximDL as soon as I get a clear night.

Subject: Constructing a Stepper Motor Focuser   
From: Assaf Berwald

The stepper I used for the focus of my 10" LX-3 was taken out of an old scanner. I used a small piece of an aluminum profile to make a bracket that would be attached to two of the three screws holding the focuser assembly to the back of the OTA.

My guidelines when I started thinking about the entire thing were:

1) The motor shouldn't cause any difficulty when swinging the telescope to any direction - mainly through the fork. Also, the motor should be placed so that it won't be damaged when setting up the telescope or when packing it into its crate.

2) The ability to manually use the focus should be maintained for any chance of a problem (ie., dead battery, dead motor or electronics etc.).

Fig. 1-- This is an overall view of the back of my 10". The focus motor is visible as well as two sets of holes for
the venting fans mounted from the inside of the OTA. The power socket for these fans is just below the back-focus.

The motor engages the focuser knob with a rubber strip that was also taken from that same scanner. The inner side of that strip has small teeth that meshes perfectly with the toothed wheel on the motor shaft. I cut a piece from one other strip and glued it on the focus know itself to prevent any slippage of the strip over the smooth aluminium knob.

The motor is mounted on one single screw used as an axle on which the motor can move and slightly change the distance between the focus knob and the motor shaft. A tension spring is used to pull the motor away from the focus knob and so a good tension of the rubber strip is always maintained.

Fig. 2-- A close-up on the unit. The black and white wires coming out of the rest of the bundle are delivering power to the illuminated reticle on the finder from the LX-3's "reticle" outlet. This saves me a lot of dead batteries as I kept forgetting to switch that reticle off at the end of observations.

Fig. 3-- A clear view of the motor mounting and the spring.

Whenever there's a need to use the focuser manually I can simply push the motor towards the focuser and as the strip gets loosened I slide it off the motor shaft to allow manual operation of the focuser.

The wiring to the motor is running on the inner side of the western fork arm. It passes through a pair of DB9 connectors on the motor end and on the other end, which is near the drive-base. That connector is where I plug in the control box which contains an on/off switch, a red-light that indicates when the box receives power, a potentiometer to control the rotation speed and two pushbuttons to operate the motor.

Fig. 4-- And here's the control box. In addition to what mentioned below, it also has a
small hinge so I can just leave it on hanging on the wedge when it's not in use.

On the side of the box is a small window through which I can see four LEDs that are blinking whenever a pushbutton is depressed. Those LEDs are indicating whenever pulses are coming out of the chip that controls the motor. With those LEDs it is easier to trace problems in the system : if the LEDs are working but the motor stands still then there's probably a problem with the wiring or the motor itself. If the LEDs stay off but the red bulb is on then there must be a problem with the electronic circuit itself. If nothing's working...well, that's probably a dead battery or some other power problem between it and the control box.

At first, I feared that the steps of the motor would induce vibrations to the telescope. Surprisingly none are visible! I tested the unit with magnification of up to x270 with no visible vibrations. Probably those are high frequency and are quickly absorbed. That's probably the place to mention that I also use a wooden accessories tray that's squeezed between the tripod-head and the wedge. This arrangement does wonders to the recovery time to the telescope from vibrations.

For any question please feel free to contact me on the list or off-list at <assafberwaldyahoo.com> Clear skies, Assaf