Appropriate moment for dome to mount sync


Hi all;

Just a Q. Is there a way to define and programm when the dome is slaved to the telescope?
I ask this because I want to avoid vibrations transmitted to the pier as my dome is kind of DIY and heavy.
I thought i read something somewhere but unable to find it?
There should be a way integrating this and i think i am not the only one concerned?
What do you guys think or know about this?

Very best & CS!!



Really noooobooody? :stuck_out_tongue_winking_eye:


I wish I could help. I imagine there is a way to do that in your dome ASCOM driver maybe?


You can setup the accuracy of the slaving and you can setup how often SGP will attempt to refresh the dome position. But we don’t currently allow the option to update only when not imaging or between frames which it sounds like what you’re looking for.

We could potentially add something that allows slaving to happen only between frames. But you would need enough width for your slot to allow you to track through the frame.



Hi guys;

Thanks for the reply! Actually I think this would interest a lot of us; i manage to do up to 1200s exposures. Most of the time i place a delay inbetween frames to manually sync the dome to the scope and also degraded both of the options mentioned above. Nevertheless I am not able to leave the dome.
Nobody else reflected on this; do I really have to rebuild my dome? :joy:





Hi Lex,
Sorry if this is way off subject, but I see from another post that you use the Lesvedome software.
I raised (what I think) were similar questions with Pierre Ponthiere a few years ago when my OBS was new.
My issue was when the dome “jogged” while tracking the scope, there was a sizable jolt to the observatory and some of the vibration made it to the pier.
I fixed the problem by adding a 30amp DC speed controller to the dome rotate circuit. By reducing the speed to a virtual crawl, startup was much softer and most of the vibration was mitigated.


I’d agree with this, I’ve written dome controllers and having some sort of soft start and stop by ramping a PWM motor power makes life easier for the dome motor and dome as well. The jerk as the motor stops or starts can, over time, damage things.




Thanks for the replies; i installed the MX066 dc motor speed controller. For sure vibrations are diminished but still present and affecting image quality if applied during sequence exposure.
My goal is to automate everything IO to remotely control the whole installation. For the moment; as I wrote above; I utilize a delay between exposures to slew the dome.
There should be a way :+1:t2:



Ultimately I don’t think that this can be solved by not moving the dome while an exposure is in progress because if the exposure is long enough the scope will move so far that it can’t see out, especially with your 20 minute exposures.

It definitely can’t be done at a lower level than the application because it needs knowledge of the exposure state and control over the dome.



1200s is the effective max exposure length if the dome slit is positioned at the minimum azimuth. I did not often expose as long only for narrowband. The dome slit comes in the FOV 2 cm or so but the center part of the image stays unaffected.
So you think that there is no way to command the dome movement inbetween exposures?

Very best



can you set the degree tolerance larger might this help?


That’s also on my test list :+1:t2:


Hi Lex,

I experience exactly the same issues with my 450kg dome. I made a post about it on this forum a few days ago, but so far without a response, see:

In it I wondered if it would be possible to solve this with an end-of-event script (or even better: to slave in between imaging, exactly as you suggested before).

As it has been some four years ago since you made your request I wondered if you found a solution in the meanwhile.



Hi Nicolas,
I had seen your earlier post, but had not commented because, for my particular situation, I had found an alternative fix. This solution does not go to your specific request but has worked for me.

I do support your request. And had raised the same several years back when I commissioned my 8’ Exploradome using their gearmotor with rack and pinion, along with the Lesvedome to drive it. In my case, when the Lesvedome system signaled “move” to the Velleman K8055 and relays, it was full power and speed instantaneously. This created a large vibration throughout the OBS which I suspected was damaging the quality of the image subs. At that time I was unable to find a way to limit dome movement to between subs.

As an alternative I added a CKMX066 PWM 12VDC 30AMP motor speed controller to the circuit. The device was infinitely variable and I was able to dial it down to minimize initial startup torque and rotational speed. Both of which greatly reduced the amount of vibration driven into the scope and mount.

Your dome is substantially heavier, and the operation is no doubt very different.

But food for thought. Hope it helps.



Hi Mark,

thanks for your response. I ordered a similar DC controller a few days ago, hope to receive it later this week. Together with a friend who helped me out with the Velleman electronics we plan to modify this controller so that it will automatically gently power up the DC motor. So instead to be running instantaneously at a fixed slower speed, to start very slow and gradually increasing to a maximum speed that can be set slower than the default speed. We will of course first test it as it comes, perhaps that is good enough already.



Sounds good Nicolàs.
Let us know how it goes.



Hi Mark,

today I installed the DC controller for the dome motor ( I found out a little too late that this controller is at times also sold with a neat housing (see Installing was dead easy, just cutting the power cable in two, adding eye-terminals at the ends and connect them to the appropriate terminals of the controller. The knob allows to reduce the speed to a mere crawl, but I fear that that may be too slow to get the dome properly running.

The tests done so far were at about 40% of the original speed and indeed it makes a significant difference. Instead of 2-4 arc second jumps in RA and DEC they are now reduced to about 0.1-0.2 arc seconds, primarily in RA (not seen anything in DEC so far, but I presume that it depends on the orientation of the telescopes which were facing the sun during the test).

I therefore still hope that SGP will be modified to have an option to do the slaving in between images or events. Jared is looking into this matter (see thread Dome slaving in between imaging or imaging events).