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Old 24-07-2014, 07:57 AM
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Octane (Humayun)
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RoboFocus and FocusMax issue

Hi all,

The following outlines my problem which I have also posted to the FocusMax User's Group on Yahoo! Groups.

The issue I'm having is that when I perform a Vcurve, the first best focus (centre) position is around the 2,000 mark (this number is not important, it's based on the step size, pause and duty cycle). On subsequent runs, the best focus position keeps shifting downwards, even though the draw tube is in the same position (as it should be). The focusing routine works (using AcquireStar), but, I'm just concerned about the fact that the best focus position number keeps changing. Once I reach a best focus position of 0, the software barfs because it thinks the focuser has no more inwards travel.

I have double-checked that my RoboFocus is secured tightly on the focuser shaft of the FSQ-106N and there's no slippage there.

My backlash setting is disabled in FocusMax and it was also disabled in the RoboFocus Control Program (have also tried enabling it with the default value of 20, as well as 40).

I even bought another RoboFocus unit, thinking it was the problem. Same issue.

I've also tried various step sizes, duty cycles and backlash settings. I make sure I start with a fresh profile after each configuration change. No joy.

The only thing I haven't tried so far is to use the new RoboFocus controller unit, with the new motor that I installed. That's easy done; I just need to swap the cables from the old unit into the new unit.

Does anyone have any magical fixes, or magical values that I should be inputting for the step size, pause, and duty cycle?

This is doing my head in. I wish to work towards a completely automated setup, and, focusing is the first step in a long list of things that need to be controlled.

To summarise: whether doing a Vcurve or a focus run (yielding HFDs of 1.4-1.6 on 4th magnitude stars), the best focus position number keeps trending downwards, eventually reaching 0.

Any suggestions?

H
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Old 24-07-2014, 08:23 AM
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RickS (Rick)
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Have you physically measured the focus position over time to see if it is actually changing to reflect the numbers from the Robofocus? If it is, then you have something going on with the scope (are you testing at times when the ambient temp is stable?) If the focus position is physically staying the same and the Robofocus position is moving then the problem is with the focuser or Robofocus. Divide and conquer!

Cheers,
Rick.
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Old 24-07-2014, 08:41 AM
cfranks (Charles)
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Hi H,

Not that it helps much but I have the same (similar) problem. My Robofocus motor and controller are about 5 years old and I use them to focus Takumar 6x7 lenses. I use @Focus2 in TheSkyX and have noticed that 'focus point number' change every time I focus but, unlike yours, my number increases. I wonder if it might be something to do with the RF Controller Temperature Compensation function but I don't use it so haven't followed it up. You can change that 'focus point number' within the RF software - Get or Set Position and Get or Set Maximum Travel - to give a big enough number that it doesn't get to zero as a test.
My system isn't connected at the moment but I can set it up indoors to do some comparisons if you want.

Charles
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Old 28-07-2014, 05:53 PM
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I don't have specific data about FocusMax but there could be 2 factors to consider. Seeing and temperature. Bad seeing can give different focal points and make focusing unrepeatable.

Temperature shifts on an FSQ cause a focus shift.

I have also had Robofocus slip at times. Do you have the correct brass coupling piece for the FSQ for the Robofocus? It makes a big difference, the wrong coupling makes the Robofocus wobble and the correct keeps it smooth.

Greg.
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Old 28-07-2014, 06:45 PM
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DavidTrap (David)
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Have you got your focus lock knob tightened?

The controller thinks it's moving the motor, but it's only moving intermittently so the numbers change while the focuser doesn't move as far as it should??

DT
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Old 28-07-2014, 09:54 PM
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Do you have a log I can have a look at H?

Have you started the control box with the out button pushed down to find the extent of travel of the scope?

Have you used the videos on Fmax website as a guide for all settings?

Going down to zero says to me that a setting is not right. Perhaps check all your numbers.

If you have a spare control box I am in the market to buy it from you if you like. I am borrowing a mates one at present after my box died over the weekend.
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Old 29-07-2014, 10:02 AM
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Octane (Humayun)
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Hi all,

Thanks for your replies, I do appreciate it.

Charles, I'm sorry you're having issues, as well. How are you focusing lenses -- are you using the belt-driven system, instead?

I honestly don't think it's a temperature- or seeing-related issue, because, V-curves are performed one after the other. If I was taking 15-minutes between V-curve runs, I would agree that it might have something to do with the temperature. I do keep an eye on the temperature units and that can't be it. Also, the seeing can't be affecting it that much, either, to continually shift the focus position number downwards in huge increments. Furthermore, I do V-curves on a star at zenith/meridian. I find the appropriate star using FocusMax, itself: take image, plate solve, sync, go into AcquireStar's settings and disable return slew, enable zenith and disable meridian flipping; it then goes and finds an appropriate magnitude 4-5 star and centres it. I then stop the AcquireStar procedure and start the V-curve run.

I have the correct brass coupling, as I bought it from Jeremy/TI directly -- I indicated what telescope I had at the time of purchase.

The focus lock knob is not tightened, it's as loose as it can be.

Paul, I don't have any V-curve log output at the moment. I just let it do its thing so I can get to imaging. I will be sending my camera off to SBIG soon, so, will have to go through the process again -- I can provide logs then. If you mean regular focusing logs, I can provide them the next time I'm on my computer at home.

I have done the calibration routine. Without it, the process won't work at all, if I'm not mistaken. The focuser doesn't slip or jam during the process, so, I don't think it has a problem with the weight of the STL-11000M.

I haven't looked at the videos on the site. Maybe that's something I can try. I just read the instructions and got it going.

I don't have a spare control box, Paul, sorry -- I'll be using both of mine. One for focusing, and, the other for the Takometer.

If you send your box to Jeremy, he'll fix it for you -- he had to do mine twice.

I suspect that if I can't get this working properly by the time my camera comes back from SBIG, I will bite the bullet and get an FLI focuser. I wanted to stick with the RoboFocus as it doesn't use any of that precious back focus distance. I should be OK with an FLI, if I do go down that route, as I don't plan on adding an MMOAG or an AO-L unit.

This hobby is truly frustrating. I don't know why we continue to bother.

H
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Old 29-07-2014, 10:23 AM
niharika
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I had similar issue with a FT3", where focus point in each v curve would keep creeping in by 40-50 steps between each subsequent run. I didn't have this issue with my last FSQ106N. My understanding is the issue is related to the focuser and not the settings in your focusmax/robofocus settings.
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Old 29-07-2014, 11:07 AM
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Octane (Humayun)
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niharika,

Is my focuser busted?

I may need to tighten things down?

H
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Old 29-07-2014, 11:33 AM
niharika
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It will come down to whether or not it's stopping you to achieve best focus. In my case i could still achieve very good focus the only awkward part was when doing the v curves I had manually adjust the focus position by approximation of 40/50 steps in ward. and once in a long while if the position was approaching close to 0 I would reset the position. Resetting position does not effect recorded v curves if settings are based on HFD in focus max.
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Old 29-07-2014, 12:11 PM
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Octane (Humayun)
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niharika,

Thank you.

Yes, I have been doing everything via HFD, so, that's good to note.

I just read the RoboFocus manual and I understand now that from the configuration screen, I can enter anything less than 64,000 in the current position box, and, it'll set it to that. That's very handy to know. I can set it to a ridiculously large number and not have to worry about it for a while (as you've mentioned). OK, so, all is not lost. It's not perfect, but, it will do for now (until I have complete automation).

I will, however, double-check and triple-check everything, again. I will tighten everything down as much as I can, from the set screws on the motor to the bracket, to the clutch, to the bracket on the focuser housing itself.

Cheers.

H
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Old 29-07-2014, 10:24 PM
cfranks (Charles)
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Yes, I use a Timing belt around the lens barrel, driven by a toothed pinion on the motor. I wonder if my 'increasing' numbers means my motor rotates the opposite direction to yours when moving, say, In? My belt is as tight as I can get it so that it doesn't slip and, as far as I can tell, the lens is at the proper focus each time.
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Old 06-08-2014, 09:15 AM
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Your problem sounds like a real pain H. Until this recent trouble I've had, I've had many years of continuous success with my RoboFocus/FocusMax only needing to rarely re-calibrate and even then I have never, ever, had to reset the position or extend the max travel or such, until this immediate problem I've had right now. I've got no idea what would be different between your setup and mine though, so many variables. My RoboFocus is on a JMI, on a SCT, and is significantly older than the units you would have if I recall timing of purchases correctly. What a pain!
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Old 06-08-2014, 11:06 AM
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Hey Roger,

Yeah, it's truly frustrating!

I finally enabled focus convergence in FocusMax the other day, with 2 steps and 10 samples. That is working even better than the usual standard focus run. It takes a bit longer, but, I'm constantly hitting HFDs of 1.4-1.7 on 4th-5th magnitude stars. That's with a RoboFocus step size of 2, as well. I suspect if I decrease that to 1, it might get even better. Now with the Moon nearing full phase, I might spend a night recalibrating with a step size of 1.

The thing that annoys me, as I mentioned in your thread, is that this has been a staple setup for FSQ/STL owners for ten years. I read nothing but positive things about it and just can't work out why I'm having these dramas. Rally emailed me with suggestions about slippage due to gravity which makes perfect sense. His suggestion of buying a bigger focuser also makes sense. Just need to wait until the funds allow such big purchases.

All I can do is tighten down the system even more than it already is. I initially noticed that when the focuser was sitting in the supplied bracket, when turning the focus knob, the whole assembly would oscillate up and down. This was likely because the bracket was sitting at an angle. I loosened everything and manually turned the knob and let the RoboFocus motor and the bracket find a happy spot where there was no more oscillation. I slowly began tightening the bracket to the base of the focuser and kept turning the focuser knob to make sure there wasn't any oscillation after each turn. This has helped a lot -- making me get down to losing 5 position units per focus run, as opposed to hundreds.

I'm now thinking that I might get a local sheet metal fabricator to make me a new bracket out of 3/16" aluminium which will get bolted down on to the finder scope bracket. The bracket base is at a 45 degree angle and it should be quite easily to manufacture and mill a bracket. This might help solve my oscillation problem, too. The supplied bracket from TI was not 90 degrees square. It's slightly acute. I emailed TI asking to buy another bracket but haven't received a reply. Will just design my own and get the local place to fabricate it for me.

H
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Old 08-08-2014, 07:23 AM
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Quote:
Originally Posted by Octane View Post
All I initially noticed that when the focuser was sitting in the supplied bracket, when turning the focus knob, the whole assembly would oscillate up and down. H
Ahhh, now that makes sense.

My focusor on the TSA worked its way loose too and wiggled a lot. You need to take off the cover plate and then tighten the screws inside the focusor; just so it is snug.

That looseness allows the focusor to slip slightly and I think it must be a common problem with Tak focusors. The focusor should not wiggle up and down after you adjust things but should still move relatively easily.

You a step of 1 too. I use that and with a sample of 10. Focus time is about 1 min 40 secs.
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Old 08-08-2014, 07:32 AM
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Just to add to that. It has occurred to me this is what was happening with my system. It started off as little jumps about 6 months ago and then it got progressively worse until it would just slip. The focusor was so loose the pinion would slip out of the rack and this I think is what is happening with your system. The Tak focusor is very robust and can hold that weight, but any looseness in the focusor will lead to slipping such as this.
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