Juwei 17/ZWO 30mm f/4 guiding issues - Forums

Topic starter

4 days ago

Hello everyone,

Ever since I switched to a mono imaging setup, my guiding performance has been much worse than before. On my previous mount, the Star Adventurer GTi, I assumed it was simply because the mount was overloaded. However, after upgrading to the Juwei 17, I'm no longer sure what the cause could be.

I've tried adjusting many different PHD2 settings and followed several recommendations from the Juwei user forum, but unfortunately nothing has made a noticeable improvement.

One thing I suspect is my guide scope, the ZWO 30mm f/4. I've never been happy with it since I bought it a few years ago. I've never been able to achieve properly focused and round stars. I've tried everything I could find, including checking the backfocus and experimenting with the focuser, but nothing has solved the problem.

I'm really hoping the issue isn't with the mount itself, as the Juwei 17 was the only realistic option within my budget. From everything I've read, other users seem to be getting excellent guiding performance with it, which makes my results even more confusing.

I've uploaded my PHD2 log below. I also tried starting a conversation on the PHD2 forum directly, but for some reason I wasn't able to.

If anyone with more experience could take a look at the log and point me in the right direction, I would really appreciate it. Thank you in advance!

PHD2 log:
https://openphdguiding.org/logs/dl/PHD2_logs_a3Wt.zip

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Tony Gondola

Frequent contributor

Exemplary contributor

3 days ago

From what I understand, PHD2 doesn’t need round stars to calculate a good centroid. Since your guiding was ok before with that guide scope, it’s probably not the cause.

Can you put up a graph of guiding session?

What was the average RMS error before and after??

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Hadi Zaheer

3 days ago

I’m just looking at the log. Did you by chance have a meridian flip just before 3am?

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Hadi Alqudihi

3 days ago

Hello Eren,

I have had the same problem with my juwei-17 mount when I was using a 30mm svbony guidescope. And I also tried to fiddle around with phd2 settings to no avail.

The problem only completely subsided when I switched to a 60mm f/4 guidescope.
Also, a “quirk” of many juwei-17 mounts is that they would need to be re-calibrated everytime before guiding.

Attached below you can find my personal guide logs.

PHD2_GuideLog_2026-05-16_001625.zip

kind regards,

-hadi

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Brian Puhl

IOTD Staff

3 days ago

Hadi Zaheer · Jul 7, 2026, 07:45 AM
I’m just looking at the log. Did you by chance have a meridian flip just before 3am?

It looks like they hit meridian and limits kicked in. It should have meridian flipped but it didn’t. Started at 63 degrees altitude + 30 degrees for ~2 hours = meridian.

Eren, I’m inclined to believe this issue is your guide scope. 30mm is a tiny scope to start with. Your sampling at 6.45 arc seconds per pixel. That means that 0.1 pixel (which is roughly your minimum move) is 0.65 arc second. Small fuzzy scope wont have much luck with that. Realistically I’d imagine you’d be able to guide around 0.3 px, which translates to an RMS of 1.8 arc seconds. Half a pixel puts you over 3 arc seconds. Your worst excursions are all generally under 1 pixel.

Make sure you’re running 16 bit mode on your guide camera as well, the SNR seems really low overall. It should help a bit. And as earlier mentioned, turn on meridian flip.

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Eren

Topic starter

2 days ago

Tony Gondola · Jul 6, 2026, 07:31 PM
From what I understand, PHD2 doesn’t need round stars to calculate a good centroid. Since your guiding was ok before with that guide scope, it’s probably not the cause.
Can you put up a graph of guiding session?
What was the average RMS error before and after??

I can’t really say that my guiding was good before that, once I switched to mono and the much tighter view my guiding was already pretty bad with the GTi. It couldn’t combat the weight good as well. RMS was definitely 1,5” to 2” with the GTi and now with the Juwei its honestly worse and I have huge spikes, more than 3”..

I dont have a graph but can upload it later, for now I will try it out with another guidescope, this time a 50mm one.
Thank you again!

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Eren

Topic starter

2 days ago

Hadi Zaheer · Jul 7, 2026, 07:45 AM
I’m just looking at the log. Did you by chance have a meridian flip just before 3am?

Yes, but since I don’t trust the mount with that as of now, I initiated and flipped it myself by slewing. It became worse after that though. I had frequent disconnects and the mount started slewing randomly for some reason. Really frustrating

Eren

Topic starter

2 days ago

Hadi Alqudihi · Jul 7, 2026, 08:15 AM
Hello Eren,

I have had the same problem with my juwei-17 mount when I was using a 30mm svbony guidescope. And I also tried to fiddle around with phd2 settings to no avail.
The problem only completely subsided when I switched to a 60mm f/4 guidescope.
Also, a “quirk” of many juwei-17 mounts is that they would need to be re-calibrated everytime before guiding.
Attached below you can find my personal guide logs.
PHD2_GuideLog_2026-05-16_001625.zip
kind regards,
-hadi

Thank you Hadi. I got myself a 50mm guidescope to test it out with this night. I will probably switch to one of the ToupTek PAPO guidescopes later on though.

I always calibrate before a session with the Juwei, with the calibration assistant. Thank you for your information!

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Eren

Topic starter

2 days ago

Brian Puhl · Jul 7, 2026, 01:19 PM
Hadi Zaheer · Jul 7, 2026, 07:45 AM
I’m just looking at the log. Did you by chance have a meridian flip just before 3am?
It looks like they hit meridian and limits kicked in. It should have meridian flipped but it didn’t. Started at 63 degrees altitude + 30 degrees for ~2 hours = meridian.

Eren, I’m inclined to believe this issue is your guide scope. 30mm is a tiny scope to start with. Your sampling at 6.45 arc seconds per pixel. That means that 0.1 pixel (which is roughly your minimum move) is 0.65 arc second. Small fuzzy scope wont have much luck with that. Realistically I’d imagine you’d be able to guide around 0.3 px, which translates to an RMS of 1.8 arc seconds. Half a pixel puts you over 3 arc seconds. Your worst excursions are all generally under 1 pixel.

Make sure you’re running 16 bit mode on your guide camera as well, the SNR seems really low overall. It should help a bit. And as earlier mentioned, turn on meridian flip.

Thank you a lot! I will try out a 50mm guidescope tonight and see if it helps. I was always unhappy with the scope. I didn’t know about the 16 bit version so I will also try that out.

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Alex Nicholas

1 day ago

If it’s of any value, I have an Emcan Astro EM31 Pro, I used to use this mount with an Askar 120APO, guiding through an OAG (so, 840mm focal length) and I would routinely see 0.3~0.5” RMS… I currently switch between a Sharpstar 15028HNT and a Redcat 51, neither of them do well with the OAG, the sharpstar due to the fact that tilt can be a concern at the far extremities of the light cone, and the redcat because I’m already pushing its boundaries with a full frame camera… So I picked up a William Optics Uniguide 32… Now guiding at 120mm focal length, I’m rarely able to achieve guiding better than 0.8” RMS… Often sitting around the 1.2” RMS mark…

I probably COULD do better with some more careful settings, but my imaging scale is ~2”/px on the 15028HNT, and 3.6”/px on the redcat, so I simply don’t care that my guiding is at worst 1.2” RMS.

Moral of the story, I went from guiding at 0.8”/px with the 840mm focal length, down to ~5”/px with the Uniguide 32, and guiding suffered pretty dramatically…

BUT - If your stars are round - who cares…

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ErykCoa

1 day ago

Hi Eren!

I own a similar mount and for me using PHD2 Predictive PEC was a game changer (https://youtu.be/BfvmlR3It1o?si=_BmrUmmIw8_XzPKL). Harmonic drive mounts have large periodic error which is apparent even with other guide setting dialed in and perfect PA. I see some periodicity in your guide error, so predictive PEC should help at least a little:

📷 image.png

The guide scope should be sufficient IMO (I’m using it with IMX290 mono camera with 0.4” RMS guiding at good night). I see some sudden spikes, so maybe your seeing was sub optimal and in that case longer guide exposures could help.

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