Strange TOA-130 behavior, drifting focal point under same conditions. - Forums

I recently setup my TOA-130 in December remotely. My scope is setup this way:

TOA-130> Moonlight Night crawler WR35 > Spacers> 645 flattener with custom precise part adapter to achieve 84.7mm backfocus from the back of the flattener > M68 plate> Player one OAG>Player one Phoenix wheel (50mm Round unmounted Chroma filters) > Player One Zeus-M Pro.

The problem I am having is when I first sent the telescope, I sent it to achieve focus in the 10000-15000 step range, with what I thought at the time to be plenty of room for changes in temperature.

What I have observed over the last two months, is the focal point kept drifting closer and closer to the objective, despite being under the same ambient tempratures. This finally became a problem last night when the autofocus point got too close to zero that it caused failure in the autofocus run and wasted more than 5 hours of perfect moonless skies.

Just to be clear, it is not just a drift due to temperature.

Here is a snapshot of my Autofocus history from January 3. You can see the Focuser point was about 11000-14000 depending on temps during the night.

And this was an Autofocus log from last night, where autofocus eventually failed because it hit zero point during the run:

I have asked the onsite technician multiple times to check if the rotator may have caused the imaging train to get looser, and they assured me everything is tight. So now I am not sure what is causing this behavior. The TOA is brand new purchased in November 2024 before it was shipped to the remote Obs.

Any ideas what is causing this?

In the meantime I decided to blast the dew heater to max temp to try to bring the focal point out, while I make a change in my adapter configuration.

Your issue sounds very much like a spacing issue. Here are my numbers, it might take a little research to translate to your setup because our optics trains are slightly different but I think your answer might be in here.

TOA with TOA645 Flattener
ASI6200MM 12.5
EFW 20
OAG 17.5
CTU 18
M68 Spacer  14 **(2) 7mm extensions14M72/M68
M72/M68 PP Coupler 4.2
645 Flattener 37
CAA M92 Tak Coupler 8mm
M92 Extensions 100mm
Total 231.2

*** M92 extensions between 645 and WR35 = 108mm to put WR35 near center of travel

TOA645 is 37mm long   FOCUS POINT 56.2mm    TOA Focus travel 77mm

Theoretical Focus point 200mm for stock TOA130 focuser, 230mm for WR35 (add 30mm)
TOA645 Metalback from M72 = 83.7mm + 1mm for Chroma filters = 84.7mm target

Your issue sounds very much like a spacing issue. Here are my numbers, it might take a little research to translate to your setup because our optics trains are slightly different but I think your answer might be in here.

TOA with TOA645 Flattener
ASI6200MM 12.5
EFW 20
OAG 17.5
CTU 18
M68 Spacer  14 **(2) 7mm extensions14M72/M68
M72/M68 PP Coupler 4.2
645 Flattener 37
CAA M92 Tak Coupler 8mm
M92 Extensions 100mm
Total 231.2

*** M92 extensions between 645 and WR35 = 108mm to put WR35 near center of travel

TOA645 is 37mm long   FOCUS POINT 56.2mm    TOA Focus travel 77mm

Theoretical Focus point 200mm for stock TOA130 focuser, 230mm for WR35 (add 30mm)
TOA645 Metalback from M72 = 83.7mm + 1mm for Chroma filters = 84.7mm target

Thanks for the input. The spacing has not changed between beginning of January and last night. Why would I easily achieve focus at 11000-15000 steps in January, and now I am hitting close to zero steps under nearly identical temps?

Theoretically, draw tube creep can cause this. It did happen to me in a couple of occasions with the Moonlite (not the NC!).

I have a similar config: TOA -> WR35 -> spacer -> 645 -> PP spacer/adapter -> Sagitta OAG -> Moravian C5

I had this same issue—except it took a year to get to the point where autofocus failed. I racked the focuser all the way in to 0 with the tech on site and he said it was still racked out about 10mm.

I exchanged emails with Ron Newman at Moonlite and he gave me a very simple fix. I just recalibrated the focuser and the focus point was restored to its original position. It took 5 minutes. Apparently it was the WR35 calibration that drifted over time.

Just connect up the Moonlite app and click the Home button. That should fix it.

My TOA-150 focus can change constantly despite very stable ambient temperature. This is particularly obvious in the first 1/3 night when day-night temperature difference is huge. My theory is that the metal tube reaches thermal equilibrium with the ambient air fairly quickly, but the three big piece of objective glass elements don't. So although the air and the metal tube have both cooled to a stable point, the objective lenses haven't. This can be particularly an issue since the three objective elements of TOA are widely separated with log of air filled in between. This makes the thermal conductivity of TOA's objective lenses very slow. It could take more than 2 hours for my TOA-150 to reach full equilibrium with ambient air after the air reaches stable temperature.

Your logs do not show the time, so I can't tell whether you are seeing the same thing as I saw on my TOA-150. If this mainly happen in the earlier part of the night and if the day time temperature is quite high at your site, then what I said above could be the reason.

Good luck. Hope you can find out the problem soon.

Timothy Martin:
I have a similar config: TOA -> WR35 -> spacer -> 645 -> PP spacer/adapter -> Sagitta OAG -> Moravian C5

I had this same issue—except it took a year to get to the point where autofocus failed. I racked the focuser all the way in to 0 with the tech on site and he said it was still racked out about 10mm.

I exchanged emails with Ron Newman at Moonlite and he gave me a very simple fix. I just recalibrated the focuser and the focus point was restored to its original position. It took 5 minutes. Apparently it was the WR35 calibration that drifted over time.

Thanks Timothy! I think that is exactly the problem but will have to wait to night time before I can prove it. Really surprised it drifted that much for a high quality focuser. After you perform the home function, does the focuser go to zero position? Because when I connect to it everything is zeroed.

I never experienced something like this with the Optec Leo.

Wei-Hao Wang:
My TOA-150 focus can change constantly despite very stable ambient temperature. This is particularly obvious in the first 1/3 night when day-night temperature difference is huge. My theory is that the metal tube reaches thermal equilibrium with the ambient air fairly quickly, but the three big piece of objective glass elements don't. So although the air and the metal tube have both cooled to a stable point, the objective lenses haven't. This can be particularly an issue since the three objective elements of TOA are widely separated with log of air filled in between. This makes the thermal conductivity of TOA's objective lenses very slow. It could take more than 2 hours for my TOA-150 to reach full equilibrium with ambient air after the air reaches stable temperature.

Your logs do not show the time, so I can't tell whether you are seeing the same thing as I saw on my TOA-150. If this mainly happen in the earlier part of the night and if the day time temperature is quite high at your site, then what I said above could be the reason.

Good luck. Hope you can find out the problem soon.

Thanks Wei! Yes the behavior early in the night is very similar to what you describe. But what I didn't understand is why the focal point in relation to the step sizes of the Nightcrawler drifted so drastically under the same conditions.

Ashraf AbuSara:
Thanks Timothy! I think that is exactly the problem but will have to wait to night time before I can prove it. Really surprised it drifted that much for a high quality focuser. After you perform the home function, does the focuser go to zero position? Because when I connect to it everything is zeroed.

I never experienced something like this with the Optec Leo.

It may be that your focuser's mechanical connection is slipping a little. Over time it accumulates. While re-calibrating, probably check that connection in the focuser.

Ashraf AbuSara:
Thanks Wei! Yes the behavior early in the night is very similar to what you describe. But what I didn't understand is why the focal point in relation to the step sizes of the Nightcrawler drifted so drastically under the same conditions.

If it’s dramatic, then it’s not what I described. The focus change induced by lens element cooling should not be much more dramatic than the change induced by tube cooling. Sorry I couldn’t be more helpful.

Wei-Hao Wang:
Ashraf AbuSara:
Thanks Wei! Yes the behavior early in the night is very similar to what you describe. But what I didn't understand is why the focal point in relation to the step sizes of the Nightcrawler drifted so drastically under the same conditions.

If it’s dramatic, then it’s not what I described. The focus change induced by lens element cooling should not be much more dramatic than the change induced by tube cooling. Sorry I couldn’t be more helpful.

The change we are talking about here is nearly 15000 focuser steps, which is equivalent to 4000 microns, or 4mm in length. So it is quite drastic change in the focal position. I really appreciate the info though Wei, it is actually helpful to understand the cause behind the nightly changes in focal position.

Rick Krejci:
Ashraf AbuSara:
Thanks Timothy! I think that is exactly the problem but will have to wait to night time before I can prove it. Really surprised it drifted that much for a high quality focuser. After you perform the home function, does the focuser go to zero position? Because when I connect to it everything is zeroed.

I never experienced something like this with the Optec Leo.

It may be that your focuser's mechanical connection is slipping a little. Over time it accumulates. While re-calibrating, probably check that connection in the focuser.

Do you mind elaborating more on this Rick? I asked the onsite tech to tighten the imaging train a few times, but I am not exactly sure I understand what the Mechanical connection you are referring to means.

Different setup, similar problem.
esprit 120, full mono imaging train, sesto senso 2.

For me the problem seems to be draw tube creep. The creep isn’t to bad in my case and i have done nothing to fix it until now. I had to recalibrate my focuser once in two years and don’t really care. If your problem is similar you could look for a set of focuser tension screws. Thats at least what i would do if the case with my esprit would become more annoying.

oh, or support your toa with a bunch of rubber bands to reduce the weight on the focuser. Pls make sure to take photos because a tak toa with rubber bands as support would be worth an image of the day

cs
anderl

I experience exactly the same thing with my TOA–130, both with the stock 4 inch focuser and ZWO EAF, and with the Nightcrawler WR 35.

As Timothy Martin pointed out, the solution is to simply recalibrate your focuser periodically. With a ZWO EAF, you have to be at the scope to recalibrate. Once I installed my system remotely, I switched to the WR 35, which can be calibrated remotely.

Frankly, I was a little surprised that the problem persisted when I made the switch to the WR 35. It seems unlikely that it could be drawtube slippage given how robust both focusers are, but that’s the only explanation that makes sense

Ashraf AbuSara:
Thanks Timothy! I think that is exactly the problem but will have to wait to night time before I can prove it. Really surprised it drifted that much for a high quality focuser. After you perform the home function, does the focuser go to zero position? Because when I connect to it everything is zeroed.

I don't recall. I think so. I do remember I had to find the focus position again. Mine is at around 40,000. The max position is around 90,000, so when I calculated the distance for the PreciseParts adapter between the 645 and the Sagitta, I tried to get as close to the center of focus travel as possible. So it was pretty easy for me to find. I think I just set it to 40,000 in NINA and then did an autofocus run and everything was fine. That was back in early December and it still focuses in the same range.

As for the Leo, remember that it's just a focuser. The WR35 is also a rotator, so that complicates the mechanics considerably.

I have an Optec Gemini on my CDK12, and I have yet to experience this kind of issue with that one. The Gemini by default calibrates every time you power it up, so that would seem to indicate that Optec anticipates some kind of calibration creep over time. I've turned that function off, so it won't surprise me if I eventually have the same issue with that one. But once you know what's going on here, it's really a minor, easy fix. I just have focuser recalibration on my list of regular maintenance tasks to do every six months or so, and I keep an eye on focus positions from night to night. I also have a Moonlite on my FSQ. No issue there yet. And I have a Litecrawler on my EdgeHD 1100--also no issue there yet (but I actually recalibrate that one pretty regularly since it's my home scope and I take it in and out of the house every few months).

I hope this works for you. I bet it will. In fact, I would bet a six-pack of Shiner on it. Please let us know!

Ashraf AbuSara:
Do you mind elaborating more on this Rick? I asked the onsite tech to tighten the imaging train a few times, but I am not exactly sure I understand what the Mechanical connection you are referring to means.

It's just a guess. When there is a gradual increase in a stepper count and the image train is the same physical length, either the motor is miscounting and that error accumulates, or there is some slippage in the focuser train with accumulating error.

If there is any clutch inside the Nightcrawler to prevent damage when hitting a hard stop, or if the focuser to drawtube connection isn't geared (Crayford), if that slips slightly in one direction (probably working against gravity) when focusing, it may would accumulate the error each time.

Rehoming should reset the error. I don't know anything about the focuser (other than the price), so I don't know if it could happen to it.

Rick Krejci:
If there is any clutch inside the Nightcrawler

There's no clutch, but the motor will stop when it meets too much resistance. I suspect it was the cold that cause my issue. It was down around -13C for about a week. The problem could probably be prevented by opening it up and putting aircraft grease in there. That will never happen for me. I'm not that handy.

Ashraf,

I have experienced the same problem since setting up my TOA130 and NiteCrawler WR35 at Starfront Observatories. My focus point decreased 10,000 steps from Oct to Dec. It decreased another 10,000 steps from Dec to Jan.

I initially thought it was just from the colder temps changing the focus point. However, the temps remained relatively stable from Dec to Jan but the focus point dropped another 10,000 steps.

I retracted the drawtube to the zero position and asked the Starfront staff to see the drawtube was actually fully retracted. They found that the drawtube was still extended about 5mm.

The drawtube position errors accumulated during winter months when the temps were often close to or below freezing. I believe that the drawtube was binding in the freezing temps.

This is the first time that I’ve experienced this problem with the NiteCrawler but it is also the first time that it has been exposed to multiple nights of freezing temps.

I suspect that the cold-temperature drawtube errors accumulate slowly night-to-night and do not affect individual auto-focus routines. If so, the errors are basically harmless as long as you occasionally run focuser calibrations during cold weather months to re-establish the actual zero position.

@Timothy Martin @Shannon Foye

Thanks for the input you were exactly right! I homed the draw tube and tonight my focal point was a whooping 20000 steps.

Really happy to know the solution was much simpler than I thought initially.

@Ashraf AbuSara, that’s excellent! I’m so happy for you!

@Ashraf AbuSara
Just saw this. Same thing has happened to me on my TOA130, as well as my FSQ106. Just like Mr. Martin has said it required a recalibration. Sounds like everything went fine for you but folks that are reading this should know that the rotater will recalibrate too. So if you havent taken your flats recently do that first. Also, if you think you may have a limited range on your rotator due to cable length, I can't remember the limit on how far it will go but I have had mine pull the cables pretty tight. I have my rotation set to only rotate 180 degrees (90deg CW and -90 deg CCW from 0). If you really need it to honor those limits for collision prevention I'm not sure it considers the set limits when recalibrating. Maybe someone else here will know.

That said despite the need to recalibrate it's a small price to pay for such a fantastic piece of equipment... I have 3! (2 WR35s and a LR25)

-Scotty

Scotty Maxwell:
So if you havent taken your flats recently do that first.

Theoretically, you could rotate right back where you were before calibration and take flats then, right? This doesn't really apply to me, so I wouldn't be able to say for sure. I only take flats about once every six months and then use the same flats for all kinds of different rotations. They seem to work fine. I guess that may seem controversial, but I know quite a few others who do this too. I can't imagine, for example, trying to take sky flats with a CDK every time I did a rotation. I'd rather have a root canal without anesthesia.

Scotty Maxwell:
@Ashraf AbuSara
Just saw this. Same thing has happened to me on my TOA130, as well as my FSQ106. Just like Mr. Martin has said it required a recalibration. Sounds like everything went fine for you but folks that are reading this should know that the rotater will recalibrate too. So if you havent taken your flats recently do that first. Also, if you think you may have a limited range on your rotator due to cable length, I can't remember the limit on how far it will go but I have had mine pull the cables pretty tight. I have my rotation set to only rotate 180 degrees (90deg CW and -90 deg CCW from 0). If you really need it to honor those limits for collision prevention I'm not sure it considers the set limits when recalibrating. Maybe someone else here will know.

That said despite the need to recalibrate it's a small price to pay for such a fantastic piece of equipment... I have 3! (2 WR35s and a LR25)

-Scotty

Yup the rotator doesn't care what limits you put when you calibrate. There is an option to calibrate just the focuser draw tube and leave the rotator alone. I had to reset my rotator position to how it was after the calibration.

I agre@Timothy Martin I only take flats once every few months. Everything between the rotator and the objective is too far out of focus to affect the flats as long as the illumination is even. The corrector and the filters / sensor all are after the rotator and will rotate simultaneously and will produce an identical flat no matter what angle you have rotated to.

I always suspected that but I got a set of flats once that when I used them they were slightly off and I could see a little crescent sliver where every dust mote was. Since then I have been overly careful. I'm sure it was probably the connection between my camera and EFW now that i think about it.

Scotty Maxwell:
I always suspected that but I got a set of flats once that when I used them they were slightly off and I could see a little crescent sliver where every dust mote was. Since then I have been overly careful. I'm sure it was probably the connection between my camera and EFW now that i think about it.

I've had similar experiences with the ZWO EFW and Pegasus Falcon. So it really depends on your personal experience. Your admonishment about getting flats before recalibrating was definitely good, basic advice for all circumstances. It can't hurt, and it could help avoid a bad situation. I'm fortunate that I can get away with what I get away with.