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Celestron Focus Motor - A Brief Review (RASA 11)

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#1 jtrezzo

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Posted 05 June 2019 - 06:44 PM

I just got the Celestron Focus Motor installed on my RASA 11 this week and have now had the chance to use it on a few nights. It works great!

 

I replaced the Feathertouch MicroTouch and Rigel nStep stepper+bracket, which I was having major issues with. It kept missing focus no matter how many different step settings I tried. (I think it was an issue with the focuser sticking more than the Rigel, something may have happened in transit during it's recent trip back from Torrance). In any case, my problem instantly went away with the new motor.

 

In SGP, I used step size of 100 (9 points) with a backlash compensation IN of 200 steps. I also told it to reverse focuser direction so that it was finishing inwards against the mirror (CCW). Hopefully this will help a few people get started with settings in SGP, though I have no idea if the RASA settings would be close to an Edge. In my experience with the Rigel on the Feathertouch on my Edge 9.25 the settings vs. the RASA 11 were close, however.

 

It also gets the focus task done much faster than the Rigel nStep. Since this is a servo motor it moves much faster RPM, and it probably also helps that I also use a much smaller step size and backlash compensation here.

 

It was easy to install even having to put on the RASA 11 retrofit kit. The only downside I can see for imaging is that it doesn't have a temperature sensor in it so you either need another solution or to just focus at a set time interval. It would have been a really nice touch if Celestron had added this. However, I used it as an excuse to order an Astromi.ch Mbox which tracks temp, humidity, and pressure and interfaces with SGP through ASCOM.

 

I am very pleased with this purchase. A couple images of the focus curve result which has excellent repeat-ability and nails it every time, and the motor installed:

Attached Thumbnails

  • focus motor rasa.jpg
  • focus curve rasa.jpg

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#2 mistateo

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Posted 05 June 2019 - 06:57 PM

Interesting.  I have seen many people frustrated with these units, but almost every case I found, the user resolved it by tinkering with the physical mounting of the unit (so lots of room for user error here).  Glad to hear that it works so well on the Rasa.  I am curious why these units are NOT compatible with the Edge 9.25 but are with all other edge scopes.  I am guessing something about the physical dimensions of the scope prevent it from working.


Edited by mistateo, 05 June 2019 - 06:57 PM.


#3 jtrezzo

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Posted 05 June 2019 - 07:09 PM

Interesting.  I have seen many people frustrated with these units, but almost every case I found, the user resolved it by tinkering with the physical mounting of the unit (so lots of room for user error here).  Glad to hear that it works so well on the Rasa.  I am curious why these units are NOT compatible with the Edge 9.25 but are with all other edge scopes.  I am guessing something about the physical dimensions of the scope prevent it from working.

The instructions were quite confusing, it made a lot more sense NOT looking at them honestly, so I am not that surprised if people are having issues mounting it. Or maybe I just got lucky putting it on and working right the first time. From what I have read it is something to do with not fitting next to the 0.7x reducer on the Edge 9.25, but it does at f/10 (but really, how many people are doing that if deep sky imaging?). 



#4 jerahian

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Posted 06 June 2019 - 04:01 AM

Jarrett-

 

Fantastic that it's working well.  Nailing the auto focus on my Edge 8 has been the hardest part for me...

 

How tight or loose do you leave the mirror locks when you use this?  How frequently do you find needing to refocus on the Rasa 11?  Has mirror flop not been an issue if you have left the locks loose between focus runs?  

 

-Ara



#5 jtrezzo

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Posted 06 June 2019 - 08:20 AM

Jarrett-

Fantastic that it's working well. Nailing the auto focus on my Edge 8 has been the hardest part for me...

How tight or loose do you leave the mirror locks when you use this? How frequently do you find needing to refocus on the Rasa 11? Has mirror flop not been an issue if you have left the locks loose between focus runs?

-Ara

Ara,
Unfortunately you can't use the mirror locks with autofocus, at least not if you don't want to do it manually every time you re-focus.

I generally leave them unlocked and just deal with the flop. There is a bit on the RASA but not crippling. I don't know if it makes any difference but I generally will leave them "almost locked" if that makes sense. I get the to the locked point and loosen them a turn. In my mind at least it gets me thinking I am avoiding any kind of extreme level of flop :) realistically I'd be surprised if it makes any difference.

As far as how often I need to refocus, I generally don't need to that often as the temp is fairly stable at night here after a certain point. Most times I refocus it ends up being the same. I have it set for every hour or 1.5 degree change (currently can't use this without temp sensor) but the once per hour is mainly just playing it safe for any kind of mirror flop issues.

#6 Lethargus

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Posted 06 June 2019 - 12:19 PM

I'll second that the instructions are near worthless on installing this thing.  I almost put the adapter plate on backwards the first time.  And they leave out the most important step for getting a successful calibration, which is setting the mirror focus to halfway BEFORE mounting.  So I had a couple mount, unmount, mount, cycles before I got mine working.

 

I think the issue with the 9.25 is neither adapter plate dimensions fit quite right for some reason.  I do wonder why it's not something solvable with a 9.25-only adapter plate.

 

I haven't had much chance to use mine, but I noticed a lot of blacklash in the motor.  I've had a very hard time getting it dialed in, but I'll give some of your step settings a shot.  Thanks for the info.



#7 andysea

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Posted 07 June 2019 - 12:33 AM

I bought this focus motor right after it came out. The USB connection kept freezing making automated imaging impossible so I got rid of it and Installed a Robofocus.

I'm glad that now these motors are working well.



#8 jtrezzo

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Posted 07 June 2019 - 12:57 AM

Sounds like I should be considering myself lucky it worked so nice right out of the box! It is purely ridiculous that they somehow forgot to test it on the Edge 9.25 before releasing though. What a joke.



#9 t-ara-fan

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Posted 07 June 2019 - 05:12 PM

   Nailing the auto focus on my Edge 8 has been the hardest part for me...

 

 

I got a MoonLite focuser for my EdgeHD 8.  A nice unit.  I can lock my mirror, and focus with SGP.   It works very well.  The MoonLite has a temperature sensor, so I configure SGP to focus every 1°C of temp change or every hour, or every 10 images, whichever comes first. It takes about 2 minutes to run the AF routine.


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#10 Phil HD9.25

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Posted 07 June 2019 - 10:09 PM

I have this focuser motor on my Edge 9.25" w/ hyperstar.  I haven't had much time to test out the auto-focus feature, so I've just been manually focusing, then locking down the mirror between targets.  Focusing is much easier now, since I don't have to keep going back and forth between the scope and laptop screen to see if my spikes are even.  Definitely worth the money even when just using it manually.  Now, if I ever want to go f/7, I'll have to go moonlight, since the celestron focuser is not compatible (the side of the focuser housing will make contact with the reducer).  I haven't tried it for visual yet, but I'm sure it's going to be a night and day difference over using the stock knob. 



#11 th3r3ds0x

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Posted 23 June 2019 - 07:27 PM

I'll second that the instructions are near worthless on installing this thing.  I almost put the adapter plate on backwards the first time.  And they leave out the most important step for getting a successful calibration, which is setting the mirror focus to halfway BEFORE mounting.  So I had a couple mount, unmount, mount, cycles before I got mine working.

 

I think the issue with the 9.25 is neither adapter plate dimensions fit quite right for some reason.  I do wonder why it's not something solvable with a 9.25-only adapter plate.

 

I haven't had much chance to use mine, but I noticed a lot of blacklash in the motor.  I've had a very hard time getting it dialed in, but I'll give some of your step settings a shot.  Thanks for the info.

I just got the focus motor for my RASA 11 and am having issues with it going through the focus.  In the directions they say to turn the feather-touch counter-clockwise until it stops.  Once the focus motor is installed it stops before achieving focus, maybe 4 turns shy.  I saw your post and was wondering if you are referring to moving the focuser on a RASA to the middle before installing the focuser.  Perhaps then it would move further through the focus and get the job done.  There doesn’t seem to be much info out there about this.



#12 jtrezzo

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Posted 25 June 2019 - 01:20 PM

I just got the focus motor for my RASA 11 and am having issues with it going through the focus.  In the directions they say to turn the feather-touch counter-clockwise until it stops.  Once the focus motor is installed it stops before achieving focus, maybe 4 turns shy.  I saw your post and was wondering if you are referring to moving the focuser on a RASA to the middle before installing the focuser.  Perhaps then it would move further through the focus and get the job done.  There doesn’t seem to be much info out there about this.

I turned it all the way counter-clockwise before installing the retrofit kit on my RASA 11. Did you run the calibration for it to find the end points? The only other thing I can think of is that the backfocus for the image train is not exact; it seems to be pretty unforgiving. I had tried with spacing off by a few mm and it would not reach focus.


Edited by jtrezzo, 25 June 2019 - 01:21 PM.


#13 th3r3ds0x

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Posted 26 June 2019 - 02:02 PM

I turned it all the way counter-clockwise before installing the retrofit kit on my RASA 11. Did you run the calibration for it to find the end points? The only other thing I can think of is that the backfocus for the image train is not exact; it seems to be pretty unforgiving. I had tried with spacing off by a few mm and it would not reach focus.

Yes I’ve removed and reinstalled a couple times.  I run the focuser full counter-clockwise until it stops before installing the retrofit.  With the motor on I calibrate and it runs to about 34 turns then reverses.  My feathertouch will go around 40 full turns so the motor basically never hits the other end running clockwise.  I did this with a star in the center of the field and a mask on the scope.  Watched the donut of the star grow smaller on my screen but it stops before getting to focus.  Maybe I should look into a replacement from Highpoint Scientific, I have about a week before I hit the 30day mark.

 

One more thing, if my back focus is off it’s only due to machine tolerance, if everything is machined exact I’m sitting at 55mm from the Celestron provided adapter.  Certainly no where near what I’m seeing on my screen.


Edited by th3r3ds0x, 26 June 2019 - 02:04 PM.


#14 jtrezzo

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Posted 26 June 2019 - 03:51 PM

Yes I’ve removed and reinstalled a couple times.  I run the focuser full counter-clockwise until it stops before installing the retrofit.  With the motor on I calibrate and it runs to about 34 turns then reverses.  My feathertouch will go around 40 full turns so the motor basically never hits the other end running clockwise.  I did this with a star in the center of the field and a mask on the scope.  Watched the donut of the star grow smaller on my screen but it stops before getting to focus.  Maybe I should look into a replacement from Highpoint Scientific, I have about a week before I hit the 30day mark.

 

One more thing, if my back focus is off it’s only due to machine tolerance, if everything is machined exact I’m sitting at 55mm from the Celestron provided adapter.  Certainly no where near what I’m seeing on my screen.

Yeah that is a mystery to me then; it sounds like you did everything right. Something is wrong. I would suggest contacting Celestron and see if they have any ideas as well. You'll probably want to do it by phone because I know when I email it can take at least a week to get a response sometimes. 



#15 44maurer

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Posted 27 June 2019 - 12:15 AM

I’ve tried mine many, many times including 2 calls to Celestron. The screw that goes down the retrofit shaft is causing me problems. If it tighten the screw the focuser will not move, so I tried to only do a couple turns of the screw and it seemed to work. BUT before I could get focus, the screw tightened to where the focuser won’t move again. My next try will be to remove the screw all together. If that doesn’t  work, back to Celestron it goes.



#16 th3r3ds0x

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Posted 27 June 2019 - 08:52 AM

Makes me wonder if the problem for you is more the retrofit than the motor. I don’t have mine on at the moment but it seems like the spacer for the retrofit is of a different thickness than stock. I tighten mine down and the retro focuser still turns free.

For me it’s almost as if it has a different calibration locked in and refuses to detect the full length of travel going only around 34 turns instead of the full 40. I may be forced to return it to Highpoint but I would rather get it working.

#17 44maurer

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Posted 27 June 2019 - 12:13 PM

Mine is definitely related to the retrofit piece, I kept trying thinking I’m installing it incorrectly. But I walked thru my steps with Celestron. I’ll give them a call again today, but I’m thinking it’s tome to return it.



#18 calvincarter

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Posted 30 June 2019 - 02:13 PM

Hi did anyone find a fix?

I’m having the exact same issue.

How much are you threading the adapter on onto the Rasa’s threaded focus rod? Instructions say “several turns”. I tried several and I tried all the way until it stopped. The latter doesn’t work at all. The former produces same results you are having.

Really frustrating. I feel like I’ve tried everything. I Think my next move is putting it back to stock.

Anyone have help?

#19 44maurer

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Posted 30 June 2019 - 03:30 PM

I’ve tried threading it so many different ways. Mine is boxed up. Would like to keep it, but I’ve tried everything I could think of.


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#20 calvincarter

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Posted 30 June 2019 - 03:54 PM

I’ve tried threading it so many different ways. Mine is boxed up. Would like to keep it, but I’ve tried everything I could think of.


Would you mind telling me what permutations you tried. Notably how much did you thread the retro kit onto the OTA threaded focus rod?

Did you put the stock back on and it worked?

And maybe my back focus train is wrong? I use an ASI294MCPRO. What do you use? Maybe I’ve got the wrong adapters?

#21 th3r3ds0x

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Posted 30 June 2019 - 06:29 PM

Would you mind telling me what permutations you tried. Notably how much did you thread the retro kit onto the OTA threaded focus rod?

Did you put the stock back on and it worked?

And maybe my back focus train is wrong? I use an ASI294MCPRO. What do you use? Maybe I’ve got the wrong adapters?

When I’ve done mine (3 times now) I rotate the focuser to the left until it stops.  Remove the feather touch, screw on the retro focuser just enough so that the screw and washer that come with the retro focuser seats.  Push the retro focuser up into the ota and secure with the orange plate and 3 stock screws.  Slide the motor on and snug it down by tightening the two screws evenly until seated.  

 

Calibrate and watch it go about 34 of the 40 revolutions.  Facepalm.  

 

Got a second unit coming tomorrow, I will report back and let you know.  

 

I did not order a second retrofit kit.  I don’t see how that could be the issue.  Once screwed down it appears to rotate free on its bearings.  If the second motor does the same I will get a second retrofit, and if that solves it I’ll test both motors.  

 

Process of elimination.  Really want this to work.



#22 th3r3ds0x

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Posted 30 June 2019 - 06:46 PM

Would you mind telling me what permutations you tried. Notably how much did you thread the retro kit onto the OTA threaded focus rod?

Did you put the stock back on and it worked?

And maybe my back focus train is wrong? I use an ASI294MCPRO. What do you use? Maybe I’ve got the wrong adapters?

One more thing, I’m using the Starizona filter slider, they make a 20mm adapter made specifically for the RASA 11.  So the 294 with the 11mm adapter, the drawer, and the starizona 20mm will get you right at 55mm from the Celestron camera adapter.  If you use a filter slider or something other than the celestron LP filter, the optical window should be removed.  Info is scarce.



#23 44maurer

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Posted 01 July 2019 - 09:19 AM

When I’ve done mine (3 times now) I rotate the focuser to the left until it stops.  Remove the feather touch, screw on the retro focuser just enough so that the screw and washer that come with the retro focuser seats.  Push the retro focuser up into the ota and secure with the orange plate and 3 stock screws.  Slide the motor on and snug it down by tightening the two screws evenly until seated.  

 

Calibrate and watch it go about 34 of the 40 revolutions.  Facepalm.  

 

Got a second unit coming tomorrow, I will report back and let you know.  

 

I did not order a second retrofit kit.  I don’t see how that could be the issue.  Once screwed down it appears to rotate free on its bearings.  If the second motor does the same I will get a second retrofit, and if that solves it I’ll test both motors.  

 

Process of elimination.  Really want this to work.

The most I could get was 4 turns, it’s definitely related to the retrofit part, because I can remove the motor, and the focuser shaft can not be turned by hand. 



#24 th3r3ds0x

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Posted 01 July 2019 - 10:38 AM

I’m pretty sure the focus shaft doesn’t turn at all. It’s moves in and out as the focuser rotates.

#25 calvincarter

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Posted 01 July 2019 - 01:54 PM

I’m pretty sure the focus shaft doesn’t turn at all. It’s moves in and out as the focuser rotates.

Yes, I think the shaft connected permanently to the OTA (the threaded focus shaft as it's called in the instructions) does not rotate, but instead just moves in and out. The focuser rotates, and is also threaded, and because it it locked into place, when turned it pushing the rod in or out.

 

The same goes for the retrofit kit piece. It rotates, you can turn it with your fingers. But the issue seems to be that you can rotate the stock focuser more revolutions than you can rotate it when you put the retrofit kit on.It's also like the retrofit kit is not allowing it to travel all the way...

 

I'm going to remove the motor and turn the retrofit piece manually to see if it will focus all the way. I bet it won't and I think others have already tried this.

Then, I'll put the stock focuser back on and see it it works. Because if it doesn't then I've got a bigger problem. ;-/




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